The levels, regulation and prognostic value of p21 in head and neck squamous cell carcinomas (HNSCC) has been puzzling for years. Here, we report a new mechanism of regulation of p21 by the mTORC1/4E-BP1 pathway. We find that non-phosphorylated 4E-BP1 interacts with p21 and induces its degradation. Accordingly, hyper-activation of mTORC1 results in phosphorylation of 4E-BP1 and stabilization of p21. In HNSCC, p21 levels strongly correlate with mTORC1 activity but not with p53 status. Finally, clinical data indicate that HNSCC patients with p21 and phospho-S6-double-positive tumours present a better disease-specific survival. We conclude that over-activation of the mTORC1/4E-BP1/p21 pathway is a frequent and clinically relevant alteration in HNSCC. The molecular pathways involving p21 and mTORC1 are frequently deregulated in head and neck squamous cell carcinomas (HNSCC). Here, Llanos et al. report a mechanism that regulates p21 stability through the mTORC1/4E-BP1 pathway independently of p53, and show that the mechanism is prevalent in HNSCC. CDKN1A gene, is a member of the CIP/KIP family of CDK inhibitors, together with CDKN1B (p27) and CDKN1C (p57). A main mechanism governing p21 levels is through CDKN1A transcriptional activation by the tumour-suppressor TP53 (p53). In response to DNA damage and many other cellular stressors, p21 levels increase in a p53-dependent manner and contribute to arrest cell proliferation. P21 also regulates multiple cellular processes, including apoptosis, differentiation and stem cell quiescence12Progression through the cell cycle in eukaryotic cells is governed by a suite of cyclin-dependent kinases (CDKs) and CDK inhibitors. Protein CDKN1A , encoded by the The serine/threonine kinase MTOR (mTOR) promotes anabolic processes and cell growth in response to environmental cues. This is achieved through two distinct multiprotein complexes containing mTOR and known as mTORC1 and mTORC2 refs , 5. The 9Head and neck squamous cell carcinoma (HNSCC) is the sixth leading cancer by incidence worldwide and is one of the most morbid, mortal and genetically diverse malignancies12131415171819We were initially motivated by the idea of studying mTOR-induced senescence in primary cells. Previous investigations had found that primary mouse embryo fibroblasts (MEFs) from knockout mice lacking the mTORC1 inhibitor TSC2 enter senescence prematurely in association with a remarkable upregulation of p21 ref. . CellulaCDKN2A; CDKN2A) or p53 (25In agreement with a previous report) or p53 , which aor p53 25. These op53-null (p53KO) MEFs by lentiviral expression of TSC2 shRNAs and p21 upregulation was still clearly observed despite its lower basal levels (p21-null (p21KO) MEFs and we observed that senescence was notably reduced compared with wt MEFs  and p53KO MEFs y shTSC2 . These o WT MEFs . Also, t WT MEFs . Finally WT MEFs . In concConstitutive activation of mTORC1 is known to shut down the PI3K/AKT signalling cascade through various negative feed-back loop mechanismsThen, we focused on mTORC1 and its proximal downstream effectors and we obtained a clue from the differential effect of mTORC1 inhibitors torin-1 and rapamycin on p21 levels28Phosphorylation of 4E-BP1 disrupts the complex between 4E-BP1 and the translation factor eIF4E, releasing free active eIF4EHaving excluded a role for eIF4E, we wondered whether p21 regulation could be the result of the interaction between p21 and 4E-BP1. We envisaged two alternative possibilities: either binding to phosphorylated 4E-BP1 results in p21 stabilization or binding to non-phosphorylated 4E-BP1 promotes p21 degradation. We addressed these possibilities by a series of immunoprecipation assays, which were all carried out in the presence of the proteasomal inhibitor MG132 to prevent p21 degradation. Interestingly, we found that endogenous p21 co-immunoprecipitated with endogenous 4E-BP1 only in the presence of torin-1, when 4E-BP1 phosphorylation by mTORC1 is completely blunted . SimilarTo further prove that the 4E-BP1/p21 complex was independent of eIF4E, we generated an eIF4E-binding-defective 4E-BP1 mutant by substituting residues Leu59 and Met60 of 4E-BP1-4A to AlaTaken together, these results are consistent with a model in which, under basal conditions, non-phosphorylated 4E-BP1 associates with p21 and promotes its degradation. In contrast, upon mTORC1 activation, the 4E-BP1/p21 complex is disrupted, and p21 is stabilized .n=274) of paraffin-embedded tumour samples from surgically treated HNSCC patients. Of note, to decrease the heterogeneity of the tumour set, we only studied HPV-negative HNSCC all of them located in the oropharynx, larynx and hypopharynx , we found that only the presence of regional lymph node metastasis at the time of diagnosis was a significant independent predictor of reduced disease-specific survival . Indeed, the p21+/P-S6+ phenotype strongly associated with improved survival in N0 patients  and lower incidence of distant metastases . A similp53 , or loss of p16, which are all common events in HNSCC111In agreement with previous studies on HNSCC12131437In summary, our results demonstrate that the mTORC1/4E-BP1/p21 regulatory axis is relevant in HNSCC, and more importantly, it favourably affects clinical outcome. These observations are not in conflict with the oncogenic role of mTORC1 in these cancers, or with the potential therapeutic value of mTOR inhibitors for HNSCC. Future studies should uncover why HNSCC with a hyperactive mTORC1/4E-BP1/p21 pathway have a better prognosis than tumours with less active mTORC1.Cell lines U2OS (human osteosarcoma), HCT116 (human colon carcinoma) and were obtained from American Type Culture Collection and were authenticated after completion of this work. Cell line authentication was performed by analysing a total of ten microsatellites at the authentication service (Genomic Unit) of the Institute of Biomedical Research ‘Alberto Sols' in Madrid. 293T cells were purchased from Invitrogen. Dr Reidar Grenman provided the HNSCC cell lines derived from primary lesions: UT-SCC-42B, UT-SCC-2 and UT-SCC-38. These cells have been previously described424344−1 puromycin for 4 days and growth in selection thereafter. The expression of 4E-BP1 mutants was induced by adding 1 μg ml−1 doxycycline to the culture medium for 24–48 h.To generate mutant 4E-BP1 inducible cells, HCT116 cells were infected with lentiviral tet-on plasmid pCW57.1 encoding the 4E-BP1 mutants 4E-BP1-4A and 4E-BP1-4A-LM-AA. The cells were selected with 2 μg ml2 and 5% CO2 at 37 °C. To grow HNSCC cell lines, the medium was also supplemented with non-essential amino acids (Sigma).All the cell lines were maintained in DMEM supplemented with 10% fetal bovine serum and antibiotic-antimicotic , and incubated in 20% OpLESIP 4E-BP1-4A mutant lentiviral plasmid in which Thr37, Thr46, Ser65 and Thr70 were replaced by Ala was a kind gift from Dr Silvio Gutkind. The mutant 4E-BP1-4A+LM-AA was generated by site-directed mutagenesis using QuikChange II XL Site-Directed Mutagenesis kit from Agilent Technologies (#200521). The pCW57.1-4E-BP1-4A Tet-On inducible lentiviral plasmid was generated in the laboratory of Dr David Sabatini and was obtained from Addgene (#38240). pBabe-puro-human-p21 was generated in the laboratory of Gordon Peters and pBabe-puro-mouse-p21 was kindly donated by Mariano Barbacid. The pMT5-Flag-p21 (human) plasmid was acquired from Addgene (#16240). The pLJM1-EGFP-Rheb64L plasmid was kindly donated by David Sabatini.http://www.wipo.int/pctdb/en/wo.jsp?WO=2010119264). This is a potent inhibitor of PI3K isoforms p110α (Ki=2.4 nM) and p110δ . The small PI3K inhibitor GDC-0941 was obtained from Shanghai Haoyuan Chemexpress, and LY-294002 was obtained from CalBiochem. Torin-1 was obtained from Tocris. Rapamycin, nutlin3, cyclohexamide (CHX) and MG132 (proteasome inhibitor) were obtained from Sigma. Doxorubicin was purchased to Pharmacia and Upjohn.The low-molecular-weight compound CNIO-PI3Ki is covered by patent WO2010/119264  from Santa Cruz, anti-human p53 (DO-1) from Santa Cruz, anti-p53 (1C12) from Cell Signaling, anti-phospho-p53 (Ser15) from Cell Signaling (#9284), anti-p19/ARF (5-C3-1) from Santa Cruz, anti-γH2A.X (Ser139) (clone JBW30) from Millipore, rabbit and goat anti-p21 (C-19) from Santa Cruz, anti-Tuberin/TSC2 from Cell Signaling (#3612), anti-4E-PB1 (53H11) from Cell Signaling, anti-phospho-4E-BP1 (37/46) (236B4) from Cell Signaling, anti-eIF4E (clone #299910) from R&D Systems, anti-phospho-S6 (Ser240/244) from Cell Signaling (#2215), anti-S6 (5G10) from Cell Signaling, anti-phospho-AKT (Ser473) (193H12), anti-phospho-AKT (Thr308) from Cell Signaling (#9275), anti-AKT from Millipore (07-416), anti-phospho-FOXO1(T24)/3a(T32), anti-FOXO1 (C29H4) from Cell Signaling, anti-flag M2 from Agilent anti-phospho-RB1 (Ser807/811) (D20B12) from Cell Signaling (#8516), anti-RHEB (C-19) from Santa Cruz.For IHC, the following antibodies were used: rabbit monoclonal Phospho-S6 Ribosomal Protein  at 1:200 dilution; Novocastra Liquid mouse monoclonal antibody p21WAF1 Protein  at 1:10 dilution; mouse monoclonal anti-human p53 Protein  and Ki67 .t-test. Data represent the mean±s.d. of independent experiments.MEFs were infected with scramble or TSC2 shRNA lentivirus and selected with puromycin for 4 days. 10–14 days after infection, β-galactosidase activity was assessed with a β-Galactosidase Staining Kit . In each experiment, β-Galactosidase-positive and -negative cells were counted in at least ten different fields. Statistical significance was analysed by a Student's two-side −1 puromycin.Silencing of endogenous proteins was performed using pLKO.1 lentiviral plasmids encoding specific shRNA sequences. All the lentiviral shRNA plasmids were purchased from Sigma: mouse TSC2-1 shRNA (TRCN0000042723), mouse TSC2-1 shRNA (TRCN0000042724), human TSC2 shRNA (TRCN0000040178), mouse eIF4E-1 shRNA (TRCN0000077475), mouse eIF4E-2 shRNA (TRCN0000077477). Control plasmid pLKO.1 scramble shRNA was acquired from Addgene (plasmid 1864). Infective lentiviral particles were produced according to the manufacturer's instructions. Briefly, HEK293FT cells (Invitrogen) were co-transfected with shRNA vectors and the lentivirus packaging plasmids PLP1, PLP2 and PLP-VSVG. The lentiviral supernatants were collected 48 h after transfection, filtered and used to infect the cell lines of interest. Following infection, the cells were selected for 3–4 days with 2 μg mlThe western blotting procedure has been previously described3VO4, 10 mM NaF, 1 mM phenylmethylsulphonyl fluoride) and supplemented with a protease inhibitor cocktail (Roche). Cell lysates (2–4 mg) were incubated with the immunoprecipitating antibody (1 μg) along with either Trueblot anti-rabbit IgG IP beads (Rockland) or protein-G Sepharose beads (GE Helthcare) at 4 °C overnight. Beads were washed four times with lysis buffer, resuspended in 2 × Laemmli sample buffer and resolved by western blotting. For immunoprecipitation, the following antibodies were used: goat anti-p21 antibody (C-19 Santa Cruz), rabbit anti-4E-BP1  and rabbit anti-eIF4E antibody . To prevent hindrance by the immunoprecipitated IgG light-chain proteins, IgG Trueblot secondary antibodies (Rockland) were used. In addition, as p21 and 4E-BP1 proteins exhibit similar molecular weights and in order to avoid interference of both signals, these co-immunoprecipitated proteins were resolved in two independent western blots. Uncropped images of all the inmunoblots can be found in For immunoprecipitation, cells were treated with 20 μM MG132 for 4–6 h and then lysed in lysis buffer  containing phosphatase inhibitors . cDNA synthesis was performed with 5 mg total RNA using Ready-To-Go You-Prime First-Strand Beads . Quantitative real-time PCR was carried out with SybrGreen Master Mix (Applied Byosystems) in a 7500 Fast Real-Time PCR System (Applied Byosystems). Reactions were performed in triplicate and normalized by β-acting expression. Primer sequences are depicted below:CDKN1A forward: 5′-GTGGGTCTGACTCCAGCCC-3′;CDKN1A reverse: 5′-CCTTCTCGTGAGACGCTTAC-3′;β-actin forward: 5′-GGCACCACACCTTCTACAATG-3′;β-actin reverse: 5′-GTGGTGGTGAAGCTGTAGCC-3′.Surgical tissue specimens from 274 patients with HNSCC who underwent resection of their tumours at the ‘Hospital Universitario Central de Asturias' between 2000 and 2009 were collected, in accordance to approved institutional review board guidelines. All experimental protocols were approved by the Institutional Ethics Committee of the Hospital Universitario Central de Asturias and by the Regional CEIC from Principado de Asturias for the project PI13/00259. Written informed consent was obtained from all patients. Representative tissue sections were obtained from archival paraffin-embedded blocks and an experienced pathologist confirmed the histological diagnosis. All patients had a single primary tumour, microscopically clear surgical margins and received no treatment before surgery. Only 12 patients were women, and the mean age was 59 years . All but 10 patients were habitual tobacco smokers, 164 moderate (1–50 pack-year) and 100 heavy (>50 pack-year), and 241 were alcohol drinkers. The stage of the tumours was classified according to 7th edition of the Tumour-nodes-metastasis system of the Union for International Cancer Control: 18 tumours were stage I, 14 were stage II, 42 were stage III and 200 were stage IV. According to Broders' classification, the series included 100 well, 110 moderately and 64 poorly differentiated tumours. None of the patients presented distant metastasis at the time of diagnosis. After surgery, and in function of the tumour stage, 164 (60%) patients received postoperative radiotherapy. HPV status was available for the whole series47Morphologically representative areas were selected from each individual tumour paraffin block: three 1 mm cylinders were taken to construct tissue array blocks as described previouslyThe formalin-fixed, paraffin-embedded tissues HNSCC TMAs were cut into 3-μm sections and dried on Flex IHC microscope slides (Dako). The sections were de-paraffinized with standard xylene and hydrated through graded alcohols into water. Antigen retrieval was performed using Envision Flex Target Retrieval solution, high pH (Dako). Staining was done at room temperature on an automatic staining workstation (Dako Autostainer Plus) using the Dako EnVision Flex+Visualization System (Dako Autostainer) and the antibodies previously described. Immunostaining was scored blinded to clinical data by two independent observers. Staining data were dichotomized as negative expression (0–10% stained cells) versus positive expression (>10% stained cells).http://p53.iarc.fr.Primers and protocols used to sequence genomic p53 from HNSCC cell lines were found at the IARC TP53 Database: P values of ≤0.05 were considered to be statistically significant.Survival curves were analyzed using the Kaplan–Meier product limit estimate. Differences between survival times were analysed by the log-rank method. Fisher's test was used to analyse two-by-two tables. For continuous variables, we used the Student's t test. Cox proportional hazard models were used to examine the relative impact of those statistically significant variables in univariate analysis. How to cite this article: Llanos, S. et al. Stabilization of p21 by mTORC1/4E-BP1 predicts clinical outcome of head and neck cancers. Nat. Commun. 7:10438 doi: 10.1038/ncomms10438 (2016).Supplementary Figures 1-6, Supplementary Tables 1-9 and Supplementary Note 1.


Laodelphax striatellus , occurs during the winter wheat harvest season in East Asia. Knowing the take-off time of emigrating L. striatellus is crucial for predicting such migrations with a simulation technique because winds, carriers of migratory insects, change continuously. Several methods were used in China and Japan from late May to early June 2012 and again in 2013 to identify the precise timing of take-off. These methods included: a tow net trap mounted to a pole at 10 m above the ground, a helicopter-towed net trap, and a canopy trap  set over wheat plants. Laodelphax striatellus emigrated from wheat fields mainly in the early evening, before dusk. The insects also emigrated during the daytime but rarely emigrated at dawn, showing a pattern that is unlike the bimodal emigration at dusk and dawn of two other rice planthoppers, the brown planthopper, Nilaparvata lugens (Stål), and the white-backed planthopper, Sogatella furcifera (Horváth). There was no significant difference in the temporal pattern of take-off behavior between females and males of Japanese L. striatellus populations.Overseas migration of the small brown planthopper,  Vanessa cardui (Linnaeus) . The number of L. striatellus trapped in this study was found to be low at dawn. The reason for this phenomenon is unknown, and a further study is needed to know how low air temperatures and other factors affect L. striatellus’s take-off at dawn in late May to early June, or other seasons as well.The bimodal take-off pattern of L. striatellus in the temperate zone of eastern China or Japan moves from a wheat host to rice plants, the population density of the subsequent one to two generations declines probably due to several factors, i.e., natural enemies, applied insecticides, and high temperatures in summer [L. striatellus emigration in summer in the temperate zone seems to be rather difficult to conduct. On the other hand, in Taiwan which is located in the subtropical region, harvest of the first crop of rice, an environmental disturbance causing emigration, is conducted in late June to mid-July and L. striatellus is one of the major pests in rice fields. Thus, investigation of L. striatellus emigration timing in summer might be more feasible in Taiwan.After n summer , 33. In L. striatellus in East Asia. Take-off times at dusk and dawn were used in a recent migration simulation model [A diurnal take-off pattern was used to predict overseas migration of on model . Based o


To examine changes in men‘s and women’s drinking in Norway over a 20-year period, in order to learn whether such changes have led to gender convergence in alcohol drinking.Repeated cross-sectional studies  of a large general population living in a geographically defined area (county) in Norway. Information about alcohol drinking is based on self-report questionnaires. Not all measures were assessed in all three surveys.Adult alcohol drinking patterns have changed markedly over a 20-year period. Abstaining has become rarer while consumption and rates of recent drinking and problematic drinking have increased. Most changes were in the same direction for men and women, but women have moved towards men’s drinking patterns in abstaining, recent drinking, problematic drinking and consumption. Intoxication (among recent drinkers) has decreased in both genders, but more in men than in women. The declines in gender differences, however, were age-specific and varied depending on which drinking behavior and which beverage was taken into account.There has been a gender convergence in most drinking behaviours, including lifetime history of problem drinking, over the past 2–3 decades in this Norwegian general population, but the reasons for this convergence appear to be complex.The online version of this article (doi:10.1186/s12889-016-3384-3) contains supplementary material, which is available to authorized users. Europeans have been called “world champions” at drinking and smoking . AlthougTraditionally, men have consumed more alcohol over more frequent drinking occasions and exceeded women in rates of heavy drinking and adverse drinking consequences, while women consistently have been more likely to be life-time abstainers , 10. TheAlthough gender roles and equality may have changed in modern societies, gender differences in drinking behaviour continue to be substantial in most cultures . HoweverThe gender convergence observed in Nordic countries during recent decades may partly be due to the increasing wine consumption , 26 in tGender convergence has not been found for all age groups or all drinking patterns in all populations studied , 30. It N = 110 060), 43 % participated in two surveys and 25 % in all three surveys [Every citizen aged 20 years or older in Nord-Trøndelag County in Norway was invited to participate in the HUNT study, which consisted of both questionnaires and clinical examinations. Three HUNT surveys were completed in three consecutive decades and for each new survey all eligible previous respondents were invited to participate. HUNT1 (1984–1986) had 77 216 participants , HUNT2 (1995–1997) had 65 215 participants , and HUNT3 (2006–2008) had 50 624 participants   and a brochure with the aims of the study and information about the examinations and procedures. At the screening station, this initial questionnaire was collected from the participants before they underwent different physical examinations. In all three surveys, the participants were given a second questionnaire (Q2) which they were instructed to complete at home and return by mail in pre-addressed stamped envelopes. In H1, all alcohol measures were located in Q2. In H2 and H3, Q1 included frequency and volume measures and Q2 included the CAGE index. The response was higher for Q1 than for Q2 , we merged these abstainers with those who never had consumed alcohol during past 12 months  to make more comparable groups. Intoxication was measured in H1 and H3, but not in H2. Estimates were based on recent drinkers in both survey samples.Estimates of abstaining, recent drinking and lifetime problematic drinking were based on total survey samples, while estimates of intoxication and alcohol consumption were based on those classified as recent drinkers. lifetime problematic drinking was assessed by the use of the CAGE index, which is one of the most widely validated screening tools for detecting alcohol abuse and dependence in primary care [In H2 and H3 the prevalence of ary care , 36. Theary care . The CAGary care .annual volume of alcohol consumption was based on beverage-specific usual quantities (number of units). Participants were asked (in H2 and H3) to separately report the amount of beer, wine, or liquor they usually consumed during a period of two weeks, indicated by bottles of beer and glasses of wine or liquors. Alcohol consumption was then calculated in liters of pure alcohol per year. A standard bottle of beer (33 cl) was assumed to contain 4,5 % ethanol, a glass of wine (12 cl) 12 % ethanol and a shot of liquor (2 cl) 40 % ethanol. Estimates of beverage-specific and total alcohol consumption were based on recent drinkers who reported any intake of alcohol during the past two weeks.Calculation of Age, education level and marital status may account for some apparent gender differences and changes in gender differences in alcohol consumption , so thesPrevalence rates, gender differences and changes in gender differences in abstaining, recent drinking, intoxication and problematic drinking were calculated for the total sample and for 10-year age groups. Since a number of the individuals in this study participated in two  or three of the surveys (27 992), these observations are considered clustered or non-independent. To account for this dependency we fitted marginal and mixed models for the binary and continuous outcomes respectively. For the former we utilized generalized estimating equations (GEE). More specifically, we specified models, with a logit link function, the correlation structure was set to unstructured, and we selected robust standard errors. Gender differences in alcohol drinking are reported as odds ratios (OR) with 95% confidence intervals (95 % CI). For the continuous outcomes  we specified linear mixed models and report unstandardized coefficients with 95% confidence intervals. In order to test for changing gender differences between surveys we included an interaction term between gender and survey. All models were adjusted for continuous age, age squared, education level and marital status. P-values ≤0.05 (two-tailed) were considered to be significant. The multivariable analyses were conducted in STATA version 13 .Table Rates of abstaining have declined in both genders Table , with grAlong with the general decline in abstaining, the proportion of recent drinkers increased from 42 % (H1) to 56 % (H2) to 74 % (H3) and in both genders (Table P = .029). The adjusted beverage-specific volume estimates . The intake of wine increased in both genders, but more in women than in men (gender difference change: P < .001). The intake of liquor declined in both genders, but more in men than in women (gender difference change: P < .001). Table The mean annual alcohol consumption (among recent drinkers) increased slightly between H2 and H3, but not for all beverages. The average intake of wine nearly doubled (0.55 to 0.98 l), while the consumption of liquors declined (0.78 to 0.40 l), from 36 % to 17 % of all intake, from H2 to H3. Table P < .001, Table Drinking to intoxication among recent drinkers was halved in H3 20 %) compared to H1 (40 %) and became less prevalent among both men and women than it was at H1, with exception of the youngest women. The absolute gender differences decreased from 25 % to 13 %  in the total sample increased from 7 % to 9 % between H2 and H3 . Among recent drinkers, intoxication has decreased in both genders, but more in men than in women. The declines we noted in gender differences, however, did not occur for all age x gender groups nor for all alcoholic beverages: they were age-specific and varied depending on which drinking behavior and which beverage was observed. For example, in the youngest age group, intoxication became less frequent in men and more frequent in women, indicating gender convergence. Some gender convergence in alcohol consumption was due to the greater decline in men’s than in women’s mean consumption of liquor.The overall changes in drinking patterns in this study are very much in accordance with previous Norwegian studies , 4, 38. Extended international travelling has not only made alcohol more available, but has apparently also influenced the drinking culture. In this study most of the consumption of liquors seems to have been “replaced” by wine drinking that increased from 25 % to almost half of all consumption (42 %) within the same period. Correspondingly, national sales statistics show that wine consumption increased 18-fold from 1960 to 2005 and made up 37% of all alcohol intake in 2012, reflecting the change in people’s beverage preferences . DespiteOur results suggest that gender differences have decreased for many alcohol measures, but that the size of the decrease varied depending on age group. This is in accordance with most previous studies of gender differences, but Norwegian men and women may constitute an exception in some aspects of alcohol drinking. Results from the cross-cultural and multinational GENACIS study showed that Norwegian gender ratios differed from most of the other countries included, although some differences were restricted to the youngest age group (18–34 years) . The GENIn studies of changing drinking patterns, there is an ongoing debate whether decreasing gender differences are due to age, period or cohort effects. Although these factors are overlapping and time effects always can be interpreted as a combination of cohort and age effects, birth cohort effects may reflect historical influences and experiences that have imprinted the life-course attitudes and behaviors of individuals born at particular times. We have not investigated possible birth cohort effects in this study, but the idea that gender convergence is most evident in younger cohorts , is partSome research has hypothesized that gender differences in drinking may become smaller as women’s rights and social status improve relative to men’s. For example, Rahav et al.,  found thOnly a few studies of gender convergence have focused on men’s drinking, but there is some evidence of changes towards more moderate drinking in men. For example, Neve et al. reported gender convergence that was explained by a decline in more highly educated men’s consumption . Saelan Although most changes in our study were in the same direction for men and women there were some desirable changes in men’s drinking that should be emphasized. The halving of intoxication in men (among recent drinkers) should be noted, since male intoxication has consistently been associated with substantial alcohol-related harm , 10. MenAnother “favorable finding” was observed in women aged 30–39 years, which is the period most (Norwegian) women give birth to and bring up children. Between HUNT2 (1995–97) and HUNT3 (2006–08) the average consumption in this age group was stable, abstaining increased, while drinking to intoxication became more rare. Problematic drinking increased, but seemingly to a lesser extent than in other age groups. Future research should investigate to what extent the culture of childbearing and childrearing in Norway may have changed to discourage alcohol consumption among women at this stage of life.Despite the possible trend towards more moderate use of alcohol (decline in intoxication) in this Norwegian population, rates of lifetime problematic drinking increased in both genders, slightly more in women than in men. While the incidence of developing alcohol problems or dependence during one’s lifetime in men seems to be stable in many countries, a recent longitudinal Swedish study suggested that the incidence among women increased between 1972 and 1997 . Anotherhttps://www.khs.fhi.no/en/health-in-the-municipalities/. Since this county lacks major cities, estimates of change in alcohol consumption may not correspond to the changes in the most urban parts of the country, but they are very much in accordance with changes reported in previous studies of adults [One advantage of the HUNT surveys is that the county surveyed, situated in the middle part of Norway has a very stable and homogenous population, with little migration and few cultural disparities related to religion and ethnicity. The repeated cross-sectional surveys of the general population located within the same geographic area, strengthen the likelihood of reliable estimates of change and comparisons across age groups and genders. The demographic stability of the county also lends strength to the idea that changes observed in drinking behaviour were cultural, and not the result of demographically different persons moving into and out of the county. The Nord-Trøndelag population has been shown to be very similar to the general population of Norway in many health aspects , 33 httpf adults , 38, 41,As in general population surveys elsewhere in the world  the partOf more concern in studies of change, perhaps, is the increasing gender imbalance in attrition and whether e.g. male responders in HUNT have become less representative of the general population. According to a previous non-response study of HUNT1 and HUNT2, attrition was moderately associated with both abstaining and heavy drinking, but was not considered a major cause of nonresponse after taking other characteristics into account . AlthougDue to the substantial decline in participation rate in HUNT3, a thorough nonparticipation study was conducted , includihttp://www.norgeshelsa.no), higher education (high school or university) was slightly more common among female responders in HUNT responders, than in this region (3 counties) and in the country, while the corresponding proportion in HUNT male responders was lower than in the country, but similar to that in the region. More important perhaps, these differences have not changed over time and thus not suggested to represent a selection bias. Although the increasing attrition, in younger men in particular, may have reduced the precision of estimates in this study, attrition is not considered seriously to limit the findings in this study.On the other hand, if gender imbalance in attrition has to do with gender specific changes in educational level, the survey samples of men and women may have become less representative for their source populations, and samples less comparable over time. According to available national statistics of men and women aged 30–39 years There are other limitations to acknowledge. First, some drinking behaviours were not assessed at all survey time points, which limits the opportunity to draw conclusions about historical trends of change. Second, variation in how questions were asked in the three surveys also makes it necessary to be cautious when interpreting the results.The validity of the CAGE as a measure of problem drinking has been debated, but our findings on problematic drinking  in HUNT are consistent with previous findings of alcohol abuse based on other diagnostic tools (DSM-IIIR and CIDI) . Skogen Adult drinking patterns between 1984 and 2008 have changed in many respects. In the current study most changes were in the same direction for men and women, but gender differences in drinking declined. Women generally moved towards men’s drinking patterns, but changes were age- specific and varied depending on which drinking behavior and which beverage was analyzed. Future attempts to prevent or reduce the negative consequences of alcohol drinking should give greater attention to gender- and age-specific changes in drinking patterns.H1, HUNT 1 conducted between 1984–1986; H2, HUNT 2 conducted between 1995–1997; H3, HUNT 3 conducted between 2006–2008; HUNT, The Nord-Trøndelag Health Study; Q1, Self report questionnaire no. 1; Q2, Self report questionnaire no. 2


To explore the co-evolution of friendship tie choice and alcohol use behavior among 1,284 adolescents from 12 small schools and 976 adolescents from one big school sampled in the National Longitudinal Study of Adolescent to Adult Health , we apply a Stochastic Actor-Based (SAB) approach implemented in the R-based Simulation Investigation for Empirical Network Analysis (RSiena) package. Our results indicate the salience of both peer selection and peer influence effects for friendship tie choice and adolescent drinking behavior. Concurrently, the main effect models indicate that parental monitoring and the parental home drinking environment affected adolescent alcohol use in the small school sample, and that parental home drinking environment affected adolescent drinking in the large school sample. In the small school sample, we detect an interaction between the parental home drinking environment and choosing friends that drink as they multiplicatively affect friendship tie choice. Our findings suggest that future research should investigate the synergistic effects of both peer and parental influences for adolescent friendship tie choices and drinking behavior. And given the tendency of adolescents to form ties with their friends' friends, and the evidence of local hierarchy in these networks, popular youth who do not drink may be uniquely positioned and uniquely salient as the highest rank of the hierarchy to cause anti-drinking peer influences to diffuse down the social hierarchy to less popular youth. As such, future interventions should harness prosocial peer influences simultaneously with strategies to increase parental support and monitoring among parents to promote affiliation with prosocial peers. In the United States, the prevalence of adolescent drinking has declined since the late 1990s—however the problem is far from being solved. Recent reports find that 71% of 9th- to 12th-grade students indicate having had at least one drink of alcohol (other than a few sips) during their lifetime, with about one fifth of them starting to drink by age 13 ,6, drug Ecological models ,11 suggePeer networks are a salient reference group for youth, with peers playing a particularly important and influential role in helping shape adolescents' evolving social worlds . VariousIn addition to shaping adolescents' friendship tie choices, peer networks also shape adolescent drinking behavior. Two important socialization processes operating in peer networks are peer influence and peer selection. Peer influence is the process wherein youth alter their behavior such that it aligns with that of their peers. Peer selection is the process by which youth select friends who are similar to themselves, on various dimensions. Adolescent alcohol use can be conceptualized as a result of both peer influence and selection processes, with friends influencing one another's drinking behavior and adolescents selecting friends who engage in similar levels of drinking –20. And Stochastic Actor-Based (SAB) models ,26 have Parents are also influential referents in adolescents' social worlds, affecting both adolescent friendship tie choices and their drinking behavior. Parents exert influences on the socialization of adolescent youth through multiple processes, including the provision of social support and parental monitoring. Indeed, parental influences have a critical impact on adolescent development, particularly in the area of building youths' social competence regarding friendship formation. One study indicated that familial factors are associated with social competence, peer acceptance, and the ability to form and maintain close friendships among youth . MoreovePast studies also demonstrate that parental influences affect adolescent drinking behavior directly. Previous research indicates that parental support prevents the early initiation of alcohol use and reduces the frequency of alcohol use among adolescents ,41,42. MIt is possible that peer and parental influences may function together in impacting adolescent friendship tie choices and drinking behavior, given insights from ecological models of development suggesting that influences from these two contexts may act synergistically . In a stFinally, we also examine the effect of depressive symptoms among adolescents on their alcohol use. Adolescent drinking has been positively related to depression in previous studies ,49–53. DThe current study builds upon extant literature examining the importance of peer influence and selection processes related to adolescent friendship tie choice and alcohol use. In addition, we also focus on the role of key parental influences on adolescent friendship tie choice and alcohol use behavior. With data from the AddHealth study, we explore the co-evolution of adolescents' friendship ties and their drinking behavior over two waves. We hypothesize that we will observe both peer influence and peer selection effects, as adolescents will select friends with similar alcohol use levels, and adjust their drinking behavior based on the drinking behavior of their friends. We also expect that parental monitoring, parental support, and the parental home drinking environment, will influence the friendship tie choice and adolescent drinking, both directly and synergistically.http://www.hhs.gov/ohrp/humansubjects/guidance/45cfr46.html. Written informed consent was given by participants (or next of kin/caregiver) for their answers to be used in this study.The data utilized in this study come from early waves of AddHealth. The respondent record/information was anonymized and de-identified prior to analysis. This study has been approved by the Institutional Review Board of the University of California, Irvine (2013). This study does not employ human subjects directly, as our analyses utilize secondary data which are de-identified. AddHealth participants provided written informed consent for participation in all aspects of AddHealth in accordance with the University of North Carolina School of Public Health Institutional Review Board guidelines that are based on the Code of Federal Regulations on the Protection of Human Subjects 45CFR46: AddHealth is a longitudinal study of a stratified sample of US schools from 7th to 12th grades . The AddAddHealth contains a saturated sample of 16 schools out of the total 132 participant schools . Among tDuring the administration of the AddHealth survey, all students in 14 schools were invited to take the survey over three waves. Information on the social and demographic characteristics of the respondents was collected, as well as their risk behaviors including alcohol use. Adolescent sociometric networks were constructed from a network elicitation item asking respondents to name up to five male and five female best friends from a name list of students in his/her school, and thus researchers are able to attain longitudinal complete sociometric networks in these schools. The measures of youths' parental contexts came from a parent survey between April and December of 1995, the same time when the respondents also took a wave 1 In-Home Survey. However, due to another administrative error, about 37% respondents in the 12 small schools and about 5% respondents in "Jefferson High" were recorded to nominate only one (instead of five) female and male best friends. To overcome this limited nomination difficulty, in this study we utilize the information retrieved from the first (In-School Survey during 1994 and 1995) and third (wave 2 In-Home Survey between April and December of 1996) time points for our dynamic network analysis, skipping that from the second time point (wave 1 In-Home Survey).The dependent (behavior) variable measures drinking frequency in the past 12 months. At wave 1, the survey question was "During the past twelve months, how often did you drink beer, wine, or liquor?" with response categories of "0—never", "1–1 once or twice", "2–2 once a month or less", "3–2 or 3 days a month", "4—once or twice a week", "5–3 to 5 days a week", and "6—nearly every day." In waves 2 and 3, the survey question was "During the past 12 months, on how many days did you drink alcohol?" with response categories of "1—every day or almost every day", "2–3 to 5 days a week", "3–1 or 2 days a week", "4–2 or 3 days a month", "5—once a month or less (3–12 times in the past 12 months)", "6–1 or 2 days in the past 12 months", and "7—never". We recoded these such that response categories specify non-drinkers (0 = never), casual-drinkers (1 = 1 or 2 days), light-drinkers (2 = once a month or less or 3–12 times in the past 12 months), medium-drinkers (3 = 2 or 3 days a month), and heavy-drinkers (4 = more than 1 or 2 days a week). gender , grade (7~12), depressive symptoms, parental support, parental monitoring, and the parental home drinking environment. Depressive symptom status is generated as a factor score of 19 ordinal items modified from the Center for Epidemiologic Studies Depression Scale  )The alcohol use and network descriptive statistics of the 12 small schools and "Jefferson High" are summarized in Among the 1,284 respondents in the 12 small schools, the number of out-going ties decreased from 6,671 during the In-School Survey to 2,704 during the wave 2 In-Home Survey due to graduation, moving, dropping out, and attrition/non-response/missing network data. A similar pattern was also observed in "Jefferson High". The proportional change of reciprocal ties was more variable in the small schools (from 0.45 to 0.33). The transitivity index, which captures the tendency for individuals to experience triadic closure, was found to be relatively stable over time, although stronger in small schools (34%) compared to "Jefferson High" (18~20%). As indicated by the Jaccard index, there was a high turnover of friendship ties in both samples, with only 21~22% of ties persisting over the two waves.The descriptive statistics of covariates are reported in b = .33, p <. 01) than in "Jefferson High" . These provide evidence of a peer selection effect, as students were more likely to select as friends others with similar levels of alcohol use.As shown in the network equation of Model 1 in b = .28, p <. 05) compared to "Jefferson High" . Adolescents having higher drinking levels were inclined to nominate fewer best friends that those with lower drinking levels, but this effect is only significant in "Jefferson High" .In both samples we also find that those drinking more frequently were more popular than those drinking less frequently, although they seemed to be even appealing in small schools  and the significantly positive reciprocity parameters  suggest that adolescents in both samples tended to form fewer ties, but when they did such ties were more likely to be reciprocal ones. The adolescents also preferred to be friends with their friends' friends (triadic closure), as indicated by the positive transitive triplets effect . The significantly negative three-cycle effect implies a tendency toward local hierarchy . Adolescents were more likely to be named as a tie if they already had many in-coming ties (high in-degree popularity) . And the negative parameter for in-in degree assortativity (square root) again suggests the presence of preferential attachment as adolescents with high in-degree were more likely to be nominated as best friends by those with low in-degree, but this effect is only significant in the small school sample .In terms of structural network effects, the significantly negative out-degree  and in the same grade . The homophily effects of parental educational levels are insignificant in both samples, after controlling for the other measures in the model.We find that homophily preferences in gender and grade drove friendship tie formation: adolescents were more likely to send friendship nominations to other adolescents with the same gender . This effect for parental support was insignificant in "Jefferson High". And we find that more parental monitoring and a home drinking environment did not affect tie choice.As for how the parental influences affected friendship tie choice, we find that adolescents who received more parental support nominate more friends in the 12 small schools : whereas higher-level drinkers were more popular in general, those with high levels of drinking in their home environment were particularly likely to form ties with those who drink more, see When focusing on the moderating effect of family contexts on friendship tie choice in Models 2 to 4 of Tables b = .22, p <. 05 in the small schools and b = .36, p <. 05 in "Jefferson High"), implying that adolescents tended to match the drinking behavior of their friends .As shown in the behavior equation of Model 1 in b = -1.78, p <. 001 in small schools and b = -1.36, p <. 001 in "Jefferson High") and the significantly positive quadratic shape effect  suggest that adolescents tended to drink less over time, but there was also a self-reinforcement effect of alcohol use: there appeared to be a tendency towards polarization on both ends of drinking behavior, as adolescents were inclined to either become or remain a non-drinker or escalate to heavy use. Popular adolescents  were not found to drink more frequently in either case. Additional significant effects were found for grade in small schools  and gender in "Jefferson High" : higher-grade adolescents in the 12 small schools and males in "Jefferson High" were generally found to increase their drinking frequency over time more than their counterparts.The significantly negative linear shape effect . Adolescents with higher levels of parental monitoring engaged in less drinking behavior over time, but this effect is only significant in small school sample . The parental support respondents received had a negative effect on the frequency of adolescent drinking, although not significant in either case.Regarding the parental influences, we find that adolescents who experienced more drinking at home were more likely to increase their own drinking frequency Click here for additional data file.S2 Fig(TIF)Click here for additional data file.S1 File(PDF)Click here for additional data file.S2 File(PDF)Click here for additional data file.S1 Table(PDF)Click here for additional data file.S2 Table(PDF)Click here for additional data file.S3 Table(PDF)Click here for additional data file.


Contextual fear conditioning is thought to involve the synaptic plasticity-dependent establishment in hippocampus of representations of to-be-conditioned contexts which can then become associated with USs in the amygdala. A conceptual and computational model of this process is proposed in which contextual attributes are assumed to be sampled serially and randomly during contextual exposures. Given this assumption, moment-to-moment information about such attributes will often be quite different from one exposure to another and, in particular, between exposures during which representations are created, exposures during which conditioning occurs, and during recall sessions. This presents challenges to current conceptual models of hippocampal function. In order to meet these challenges, our model's hippocampus was made to operate in different modes during representation creation and recall, and non-hippocampal machinery was constructed that controlled these hippocampal modes. This machinery uses a comparison between contextual information currently observed and information associated with existing hippocampal representations of familiar contexts to compute the Bayesian Weight of Evidence that the current context is (or is not) a known one, and it uses this value to assess the appropriateness of creation or recall modes. The model predicts a number of known phenomena such as the immediate shock deficit, spurious fear conditioning to contexts that are absent but similar to actually present ones, and modulation of conditioning by pre-familiarization with contexts. It also predicts a number of as yet unknown phenomena. During Pavlovian fear conditioning, animals become afraid of both specific cues that predict the imminent onset of aversive events such as foot shock, and the situation or “context” in which the shock occurred. Fear conditioning provides one of neuroscience's most promising and active arenas for analyzing neural mechanisms of learning, generally. Both cue and context fear conditioning seem to be due to plastic change at synapses within the amygdala  that are present over extended periods of time. It can be expected that brains come to a learning situation pre-wired to represent the simple cues that, at least in the laboratory, are usually used as CSs for imminent USs. Such cues may be made to evoke fear simply by strengthening synapses between these representation neurons and amygdala fear-producing cells , was not considered but it is planned to address it at a later time.V) are specified relative to this baseline. Active synapses are thought of as causing post-synaptic conductances for specific ions. Excitatory input moves V toward an excitatory reversal potential E. Active synaptic inputs to a neuron cause post-synaptic conductances given by G = A ▪ W where G is conductance relative to membrane leakage conductance, W the synapse's strength or “weight,” which can vary from zero to any positive value, and A the activity level  of the presynaptic neuron. The net depolarization of a neuron receiving both excitatory and inhibitory input is given by:The resting potential of BACON neurons is taken as zero, and membrane potentials  and reaching a maximum of unity at a higher voltage (mxat). We refer to this as a “linear sigmoid activation function,” which we write as follows:The basic cortical-hippocampal-amygdala circuit of BACON is shown in Figure Most of the computations done by the algorithm are explained in logical or mathematical terms. Actual neural circuitry that could underlie them is unknown, but circuitry that could compute the Bayesian Weight of Evidence, which is central to the model, and circuitry that could use it to control hippocampal and amygdala function are sketched out to demonstrate that they could be carried out by neurons. Ways of carrying out arithmetical operations such as subtraction, multiplication, exponentiation, etc. assumed done within this hypothetical circuitry and ways of implementing K-Winners-Take-All control of neural firing, used extensively in BACON, are discussed in the Supplementary Material (Topic H).The values and definitions of BACON's parameters are summarized for reference in Table A flow diagram of the computations done by BACON is provided in Supplementary Material (Topic G).appended with a prime (') mark.The goal of this work was to construct a biologically plausible algorithm/automaton for context fear conditioning. It is assumed that upon entering a context its attributes are observed (“sampled”) serially in random order without replacement over an extended period of time and are held in a working memory. As attributes are sampled, we wanted the automaton to compare them to the recalled attributes of previously experienced contexts and use the comparison to decide whether the context is a known one, in which case existing associations to it should be expressed and new ones made, or a novel one, in which case a neural representation of it should be created and further associations made to that. The algorithm we have created deals with these matters using analogs of cortical, hippocampal, and amygdala structures; we name these for their biological counterparts Figure CtxN (=1000) input (EC'in) neurons, each of which innately represents one of the possible contextual attributes that the automaton can detect. Hippocampal output back to cortex is via a corresponding set of output (EC'out) cells. Each context is composed of AN (=100) attributes of which a number, GenN (=50) are general to all contexts. When an attribute is sampled the EC'in cell that represents it becomes active and remains so for the duration the visit to that context. Neurons that remain active during a working memory task have in fact been found in entorhinal cortex  that consists of HippN , of projecting neurons that during representation creation recode the EC'in pattern of activity into a sparse, relatively non-overlapping form  EC'in neurons. All of BACON's Hebbian synapses are totally ineffective until potentiated. During representation creation, firing of the projecting DG' neurons is subject to regulation by an inhibitory network that allows only a specified number of the most excited cells to fire (“K-Winners Take All” (KWTA) behavior). When operative, this allows K =60 of DG's 10,000 cells to fire. At other times, DG' cells fire at a rate proportional to their excitation.DG' consists of a large number, in both via DG' (the “indirect” pathway) and via a direct pathway from EC'in. As was the case for DG', each CA3′ cell is innervated by F randomly chosen EC'in neurons, but these are chosen independently of the DG' innervation. In the biological hippocampus each CA3 cell is innervated by a small number of dentate cells, and the synapses, which appear from morphology to be strong, show some non-Hebbian sort of plasticity of uncertain function  We believe that it is consistent with the weight of available evidence  Hippocampal representations of very similar contexts overlap much less than do cortical ones, which makes discriminations easier to learn. (iii) Hippocampal representations are (by construction) constant whereas cortical ones change as more is learned about a context; changing representations would lead to unwanted variations in expression of previously conditioned fear.Although we assume that hippocampal circuitry evolved to allow reconstruction of the neocortical activity that occurred during past events, or downstream, possibly cortical, versions of it), and not cortical attribute-representing neurons themselves, to which contextual fear responses become conditioned.The actual  pathway via which information about active hippocampal representations reaches the amygdala from the dorsal hippocampus is a matter of current research. Based on various lines of anatomical, and more recently labeling and optogenetic data, ventral hippocampus as well as various cortical structures have been suggested as possibly being on the relevant pathway Maren and Holt, CA3′ innervates amygdala' fear-producing cells via Hebb synapses, and conditioned fear develops when synapses between active CA3′ cells and amygdala' neurons that are depolarized by an unconditioned stimulus become potentiated.creation or recall as well as controlling conditionability and the expression of previously conditioned fear. This control is exerted by enabling or disabling the possibility of Hebbian potentiation, modulating the strength of certain synapses, and turning on or off the KWTA capability of those regions that are potentially subject to it. The idea that hippocampal circuitry is subject to task-based reconfiguration has precedents in the work of O'Reilly, McClelland, Rudy, and Hasselmo , and (3) enabling the KWTA circuitry of DG' . Finally, the strength of transmission at DG' to CA3′ synapses is up-modulated sufficiently so that the K cells that will fire in CA3′ will be the partners of the K winners of the DG' KWTA competition and not be affected by direct EC'in input.When BACON decides it is in a novel context, it configures the circuitry of Figure n Figure . This inK DG' cells that are most strongly excited by the active EC'in attribute cells fire and drive their CA3′ partners. The synapses between all active EC'in cells and the active DG'-CA3′ partners then become potentiated. It should be noted that this method of determining which DG' and CA3′ cells come to represent a context ensures that the representations will be composed of those DG'-CA3′ “dyads” whose DG' member is most strongly innervated by the EC'in cells representing the attributes that had been sampled up to the moment of the representations creation.Under these conditions the K most excited CA3′ neurons fire, the activity of each active CA3′ cell propagates into its dendrites and collaterals, and the recurrent synapses between one active CA3′ cell and another potentiate. The permanent representation of the current context has at that point been established as the active set of DG'-CA3′ dyads. It is the potentiated recurrent collateral synapses that bind together the set of cells that comprise a representation, and it is the potentiated synapses in the direct and indirect pathways that are responsible for the ability of a given context's attributes to call out its proper representation. Finally, the synapses between the active CA3′ representation neurons and the set of active EC'out attribute cells that are being driven by the active EC'in cells become potentiated so that in the future when this representation becomes active it will cause those same EC'out cells to fire.Once the in attribute cells active.It should be noted that, as will be explained below, representation creation generally occurs when only a portion of a context's attributes have been sampled. Therefore, even if two contexts are extremely similar, their representations will be created with somewhat different sets of ECIn some biological experiments to be discussed, DG' was inactivated during encoding. If this is done in BACON, it will be the KWTA properties of CA3′ operating on input via the direct path that will determine which CA3′ neurons comprise the new representation.recall. In this mode , the effect of whose value we study below. KWTA control is disabled in DG' during recall, with the result that cells there fire at rates proportional to their excitation; however KWTA control is always operative in CA3′.In the resting state, the cortical and hippocampal parts of Figure e Figure  no synapin neurons excite DG' and CA3′ cells via any previously potentiated synapses. The DG' cells fire in proportion to their excitation, exciting CA3′ cells proportionately, and the direct input from EC'in sums with the excitation from DG'. The KWTA rule then determines CA3′ firing. The pattern of activity at this stage we call CA3Ptrno.Under these conditions active EC'CA3Ptrno will mostly be ones that were active when a context's representation was created. However, earlier in sampling, when only a modest fraction of the total set of a context's attributes have been sampled, it can easily occur that representation cells that do not represent the current context will be part of CA3Ptrno. This happens because, as mentioned above, when two contexts have attributes in common , which of these get encoded when their representations are created is usually somewhat arbitrary. Therefore, during recall in one of the contexts, shared attributes that were encoded for the other context may well be the ones first sampled and may cause representation cells unique to this (incorrect) context to be activated.Once sampling of a context's attributes is fairly far advanced, the strongly excited cells included in CA3Ptrno will generate a new pattern of CA3′ excitation via the potentiated synapses of the recurrent collateral system, and the K most excited cells will again fire. This process repeats a specified number of times until a final pattern referred to as CA3PtrnFnl results. In BACON, where each CA3′ cell recurrently innervates each other one, a CA3Ptrno in which a plurality of the cells are part of some representation will, after two iterations generate a CA3PtrnFnl in which the cells active are the K representation cells for that context and no others . If no context's representation cells are in a plurality, CA3PtrnFnl will consist of more than K cells (a summation of more than one representation), and in that case no downstream activity will be produced  of the active CA3′ cells fire.Finally, update mode  that an active hippocampal representation really is that of the current context. It then uses this value to decide whether to create a new representation or update the current one, whether to permit fear conditioning if a US occurs, and whether to allow expression of conditioned fear.Based on comparisons of current EC'RepB is based on (1) the number of attributes of the current context that have been sampled and have active representations in EC'in (referred to as curZ –for “currentZ”), (2) the number of attribute representations activated in EC'out by the current hippocampal representation , and (3) the number of active attribute representations in common between EC'in and EC'out (comZ–for “commonZ”). RepB is defined as:The calculation of RepB as a function of comZ for a range of values of curZ and recZ; the combinatorial formulas used to calculate these values are given in Supplementary Material (Topic C). High positive values mean that the specified degree of communality between EC'in and EC'out activity makes it very likely that the actual current context is in fact the one that was present when the currently active hippocampal representation was created. A large negative value indicates that the actual current context is not the one currently represented by the hippocampus. A value of zero means that there is no basis for believing either hypothesis. We note that BRep = 0 if EC'out remains silent, as it does when the number of cells active in the initial CA3′ pattern of the computation cycle (PoX) is less than 0K .Figure Zcur = 60. (1) For any given number of current and recalled attributes, the greater comZ, the more likely it is that the currently active representation is in fact that of the current context, and correspondingly, RepB increases as a function of comZ. (2) The more one recalls about the context one thinks one is in, the more strongly a low value of comZ implies that one is actually somewhere else, and conversely. Consistent with this, for a given value of comZ, RepB decreases as recZ increases. (3) If the number of currently observed attributes that are different from ones remembered (cur–ZcomZ) plus the number remembered (recZ) is greater than the number of attributes there are per context (AN), then the current context cannot be valid. Consistent with this, RepB goes precipitously negative if cur - Zcom + Zrec > NAZ.The relationships shown in Figure on average the current context could be identified with assurance. Figure RepB values for the theoretically predicted average (referred to as “expected”) comZ for a test in the conditioning context; we refer to RepB so calculated as RepExpected B. The greater recZ due to experience with the context in prior sessions, the faster RepExpected B rises as more attributes are sampled in the test session.We will later discuss experiments in which animals are pre-familiarized to contexts in which they will subsequently be conditioned. Intuitively, it would be expected that the more attributes of the context were previously learned, the sooner This section describes the logical rules used for controlling the state of the basic circuit; neural circuitry for implementing these rules is discussed separately.RepB  that determine the mode of operation . As explained in the next section, this is the level at which conditioning begins to become possible. If RepB exceeds this value, we speak of the current context as probably being “known” or “familiar.” addB is taken as the level of RepB at which the automaton is virtually certain that the current representation is valid, and at which attributes are therefore allowed to be added to active representations . We note that it is crucial that a representation not be updated unless it is almost certain that it is valid, because adding invalid attributes to an existing representation would render it valid nowhere, and any conditioning that had occurred to it would be lost to effective usage. Therefore, addB is made much higher than oldB .We define certain levels of n Figure  of the bld Table . Bnew isRepB falls below newB, creation mode  representation for the same context. To reduce the likelihood of this happening, representation creation is suppressed if during the session, some representation has generated a RepB sufficiently positive that it is likely to be the actual representation of the context; the degree of positivity required is pvB , and for the simulations of this paper this was set equal to oldB. This rule helps prevent unwanted representation creation; however, if the automaton is placed in a new context that is quite similar to a familiar one, the representation of the familiar context is likely to be activated and may generate a quite high RepB value  may remain below 0K, EC'out remain silent, and RepB remain zero, even after sampling considerable numbers of attributes. In such cases a new representation is created if the number of cells active in the pre-recurrent input activity pattern of CA3′ (PoX) is still less than 0K by the time curZ reaches 0Z.Given the above rules, creation of a new representation will usually occur when an active representation generates a Finally, if a new representation has just been created, it is by definition valid for the remainder of the session; therefore updating occurs at every subsequent sample of the session.Context fear conditioning in BACON is due to LTP of CA3′-Amygdala' synapses, which occurs at synapses between active CA3′ neurons and amygdala' cells when the amygdala' cells are depolarized by a US :Cnd = 0 when expected BRep = Bold. RepB increases both earlier and faster with increasing recZ because the more that is known about the context, the faster RepB increases as information about the current context is acquired.We thus make conditionability increase linearly as a function of the degree to which er Table . The bladuring sessions where representations were created.This much is straight-forward and we believe plausible. However, special issues arise when USs occur 0Z (the minimum curZ at which a representation can be created). We argued above that given BACON's parameters, 0Z should be at least 10. However, if 0Z were in fact 10 and we introduced BACON into a new and distinctive context, a representation for the context would then be created at sample 10. Since, as pointed out above, a representation is by definition absolutely valid for the remainder of a session in which it is created, conditionability should at least start to rise from zero at that point. However, suppose we were to remove BACON from the context right after the representation was created and then later re-introduce it. Since recZ would now be only 10, all AN (=100) attributes would have to be sampled before RepB rose to oldB and conditioning became possible. That would leave us with the peculiarity that conditioning becomes possible after 10 samples in a fully novel context but only after 100 in one with which the automaton is already familiar. In order to prevent such an anomaly, 0Z would have to be such that RepExpected B on a session following an initial one that terminated just after 0Z samples, would reach addB once this same number of samples were made in the latter session . Reference to Figure Z0 = 45, which value we have used for the simulations of this paper.One of these concerns the value of rate at which Cnd should increase if the automaton is left in the context after creation of the representation. Basing Cnd on RepB calculated from cur, ZrecZ, and comZ seems to make sense when BACON is in-essence making a statistical inference as to its whereabouts. However, if a representation for the current context has just been created, BACON can in-effect be certain that its active new representation is valid. Thus, it might plausibly be argued that once the representation is created, conditionability should jump to unity for the remainder of that session, as indicated by the dashed step function in Figure Cnd should not go down in a later session with the same information. In that case, the upper limit for Cnd on the session of a representation's creation would be the value it would be expected to have given random sampling of attributes on a later session. The bold red dotted curve of Figure The other issue concerns the gradually from zero following the period during which no conditioning is possible  produced by a potentiated excitatory CA3′-amygdala' synapse be dependent on RepB, being zero when BRep = 0 and becoming equal to its full potentiated value eG when RepB = addB  because we suppose that it is better to err on the side of being afraid. The actual expression of fear is proportional to the depolarization AmygV that is produced by the conductance e'G:RepB rises during a session  is replaced by RepExpected B. This is used in computing post-shock freezing.During a session where representation creation occurred, Although the above logical description of the BACON algorithm fully characterizes its operation (and provides a sufficient basis for reading later sections), it is important to make clear that the operations specified above could in fact be carried out by neurons. There would be many ways of doing this; we sketch one here.RepB (posB)for controlling Cnd and fear expression. Control of plasticity is assumed to be via direct effects on synaptic properties, though one could imagine the possibility of indirect control via modulation of firing rates. We note that the work of Hasselmo , rather than time, as an independent variable. However, a few comments about time per se are needed: The earliest that a representation can be created and conditioning occur is at sample 0Z, and the earliest time that conditioning begins in rats is about 30 s  attributes are sampled per 30 s. However, we presume that any plausible theory of sampling would have sampling slow greatly from this rate as the proportion of total attributes sampled approached the total available. Indeed, we imagine that it would be rare for full knowledge of a context's attributes to ever be achieved.Conditionability and fear expression will vary over time, dependent on what attributes are randomly sampled. In order to avoid proposing a theory of sampling over time, which is a complex topic of its own, we use sample number  and after the final iteration of such input (CA3PtrnFnl). In both simulations there was a mix of elements of each representation active prior to recurrent collateral input, but in the post-recurrent input representations, whichever pattern had the most active elements prior to recurrent input prevailed. Moreover, as sampling progressed, the valid representation increasingly predominated. When A and B were quite different, the final output of CA3′ was the valid representation starting fairly early in the session; when they were quite similar, it took many samples before the final representation was consistently the valid one.Figure dpf. In simulations I and II only the indirect pathway was operational (dpf = 0). Figure dpf in simulations like those in I and II. As expected, the indirect pathway produces better separation than the indirect one, but both together are best. However, the advantage of incorporating input from the direct pathway is modest and is seen only if input from the direct pathway is relatively weak. For simplicity's sake we chose to use only the indirect pathway  in the simulations below.This sort of simulation provides a good opportunity to evaluate the consequences of using the direct vs. indirect pathways during recall. As will be explained in Discussion, it was expected that use of the indirect path alone during recall should lead to more reliable activation of the actual current context's representation than use of only the direct one. However, both operating together should produce somewhat better performance than either operating alone. The ratio of strength of direct path to indirect path synapses in recall mode is the parameter CA3PtrnFnl becomes the complete representation of context A early in the session. On the other hand, when placed in a different unfamiliar context B that was moderately similar to A, the hippocampus initially activated the representation of A, but eventually  created a new representation for B.Having considered the activity of the hippocampus alone, Figure RepB for the active representation throughout the simulation, with which representation was active indicated by point color. When in context A, the representation of A became the sole representation active at sample 15 (black circle point 3). This allowed EC'out neurons to be activated , the representation of A was activated early on Figure . The att8 Figure , with a 8 Figure , but by 8 Figure  that BRein cells, and the firing of only the K most excited, promote pattern separation; these factors cause contexts with 90% overlap at the level of ECin to have about 30% overlap at DG' during representation creation. Second, contexts are generally created when only a fraction of their total attributes have been (randomly) sampled. With this factor operating along with the first, overlap of the representations for 90% similar contexts falls to about 10%. As a result, even when two contexts are extremely similar, relatively distinct sets of attributes will control the form of their representations and very different representations result.Representations in BACON, even of quite similar contexts, have only limited overlap  process produces considerable “pattern separation”). Two factors contribute to the slightness of overlap. First, as often discussed, the large number of DG' neurons, their innervation by random groups of EC0Z. Conditionability begins to increase at this point and continues to do so as curZ increases, until it reaches its maximum value of unity  conditionability begins to rise when RepB reaches oldB. The more that is known about the context's attributes  at the start of the session, the sooner oldB will be reached . Figure RepExpected B which is an increasing function of both curZ and recZ, and whereas recZ increases at each successive sample during the session of encoding, on later sessions it is constant throughout a session unless RepB comes to exceed addB.If placed in a  Figures , 6A. Fig0Z. Therefore, even many repeated exposures to the context, each of which is too short for 0Z samples to be made, will not reduce the immediate sock deficit. Moreover, attributes cannot be added to an existing representation unless RepB exceeds addB. Therefore, once BACON has been familiarized sufficiently with a novel context to allow some measure of conditioning, further later exposures will only be effective in shortening the immediate shock deficit if some of the exposures are long enough to allow RepB to exceed addB. To our knowledge no experiments that would evaluate either of these features have been published.It is a basic feature of BACON that the attributes of a novel context cannot begin to be learned until a hippocampal representation is formed, and this cannot occur until the number of samples made exceeds Fear expression in BACON develops gradually when the automaton is introduced into to a feared context Figure . As illuRepB reaches addB, both become maximal at about the same time  The hippocampal representations of the two contexts may have neurons in common. (2) The vicissitudes of attribute sampling may sometimes cause periods of activation of the hippocampal representation of a familiar context Degree of context fear generalization is very dependent on the extent to which the automaton is already familiar with the context in which generalization is tested. Figure recZ), the more rapidly a similar context will be recognized as different. Decreased generalization of stimuli that are better known has been observed both for context fear and other forms of conditioning . This happens because the better-known the conditioning context . If a US were given at the point marked “Early” fear would be conditioned to context A, if given at the “Middle” point, each representation would be active in about half the runs, and if given “Late,” conditioning would be to context B.Rudy and O'Reilly  have pubHad BACON been pre-familiarized with a context, D, very different from B, conditioning at the corresponding points in the experiment would always have been to the actual context, B Figure .Fear expressed in each context after giving BACON USs at one of these three points are shown in Figures The algorithm described here was an attempt to construct a neurally plausible mechanism for context fear conditioning. The role of the hippocampus in this is the creation and subsequent recall of permanent, relatively non-overlapping representations of contexts to which associations can be made. We assume that at each entry to a context its attributes are discovered serially in random order. Since attributes of a context will be sampled in different orders on different occasions, and since information about a context will usually be incomplete when its representation is created, determining whether a context is novel (in which case a representation for it should be created) or familiar  is a challenging problem. This led us to construct for BACON extra-hippocampal machinery designed to make optimal decisions as to the novelty or familiarity of whatever context it was in, and then to allow this machinery to configure the hippocampus specifically for representation creation, updating, or recall, as required.This strategy solves two problems that arise if the hippocampus is assumed to have only one state:In conventional theories of the hippocampus the occurrence of a novel stimulus configuration that is similar to one previously encoded may activate the complete code of the familiar stimulus with the result that a new representation will not be created but its attributes will, improperly, become associated with the existing representation. Or conversely, in the presence of a known stimulus, incomplete sampling of its attributes or sampling of attributes not originally encoded will cause a new representation for it to be created so that one stimulus will now have two different (pattern-separated) representations. This is the so-called “pattern separation-completion tradeoff” that has been extensively discussed in the literature  pathway, it has been argued, and is often accepted, that properties of the indirect pathway that are needed for optimal representation encoding make it impossible for the pathway to also be used effectively during recall  2–3 of them. The synapses of the active attribute cells on the K DG' and CA3′ cells of the forming representation will become potentiated. In CA3′ it will be the approximately 2–3 active EC'in-CA3′ synapses that innervate each cell that become potentiated. However, in DG' the cells that are active will be selected as the K that are most excited and therefore most heavily innervated by the active EC' attribute cells. The DG' cells that are active will therefore have a richer active EC' attribute cell innervation than will the population as a whole, and it will be some 7–8 synapses on them that will become potentiated.Since, as discussed above, we can ignore computational arguments against a role for the indirect pathway during recall, we consider the relative merits of using it vs. the direct one: Each DG' and CA3′ cell will be innervated by in only via potentiated synapses. In order for a representation cell for a context A to be selectively activated by context A, as opposed to a different but similar context B, a representation cell for A must receive effective input from attribute-representing neurons that are specific to A, and if A and B are very similar, there will not be many A-specific attribute neurons. So when very similar contexts must be differentiated, the DG' cells, which get effective input from 7 to 8 EC'in cells, are more likely to get input from a given attribute (which will be passed to a cells CA3′ partner) than will the CA3′ cells, which get effective input from only 2 to 3 EC'in cells. Thus, if only the direct or only the indirect pathway were used for recall, the indirect would be better because it would be more likely to provide effective input from a context A-specific neuron. However, if both the direct and the indirect pathway provide information that determines the response of CA3′ cells prior to recurrent input, differentiation should be somewhat better than with either pathway alone. As shown in Figure CA3Ptrno) as a function of the relative strength of the direct pathway is in fact just as expected. Moreover, it seems to be optimal for the direct pathway to be weak relative to the indirect one. This may be seen as consistent with the biological situation, where both pathways are present, but the direct one makes relatively distal synapses on CA3 neurons.During recall, DG' and CA3′ cells receive information from EC'out directly, rather than via a CA1-like processing stage because complete innervation in the recurrent collateral network and in EC'out made a CA1′ redundant. Since it is the Shaffer collateral synapses of CA3 cells on CA1 neurons that have told us much of what we know about Hebbian LTP, it may seem ironic that we did not explicitly include a CA1 in the algorithm. However, in the current model, the Hebbian nature of EC synapses on dentate and CA3 cells are sufficient to produce effective encoding and recall of contextual representations. In a model of this type CA1 plasticity would serve mainly to help mitigate any errors or omissions that remained in representations after their processing by the recurrent collateral network.As explained at the start of Results, we have allowed CA3′ to innervate EC'There have been a number of experiments in which activity in dentate or CA3 in novel or familiar contexts has been assessed or manipulated. We consider here how BACON would behave in some of these.RepB will fall below newB and a new representation will be created. For the remainder of the session, as each additional attribute gets sampled, excitation will be passed to CA3′ over the direct and indirect pathways, CA3PtrnFnl determined, and since the system is in Update mode, CA3PtrnFnl will be reflected back to DG' so that the synapses between the added EC'in attribute cells and DG' cells can potentiate. From then on in each computational cycle hippocampal activity will consist of the K DG'-CA3′ pairs of cells of the current representation fully active, with the rest of the cells of each layer silent. Moreover, these active cells will overlap relatively little with those of other representations. Consistent with this, it does appear that, whereas there is a lot of overlap between the DG' cells active in different familiar contexts, during exposure to novel contexts DG' activity is quite context-specific, even when the contexts are similar  at which time Update mode will begin to operate; we will assume for discussion that it is mainly Recall mode that will be observed during most experiments. During recall, it is DG's job to pass to CA3′ information as to how much excitation each DG' cell has received from EC'in; therefore, during recall the KWTA rule does not apply in DG', and cells there fire in proportion to their excitation. Thus, in DG' any cell that represents an encoded context having attributes in common with the current one will fire to some degree. However, in CA3′ the KWTA rule is operative. CA3Ptrno will typically include cells  that do not represent the current context, because some representation cells of other previously encoded contexts may happen to have dense innervation from common attributes that happen to be in the current attribute sample. However, CA3PtrnFnl, once it emerges, will (if enough attributes have been sampled) be the complete representation of the current context and will overlap little with the representations of other, even similar, contexts. We assume for the sake of discussion that it would be mostly this final pattern of activity that would be detected in experiments. In fact, recordings from real animals do seem to show that in familiar contexts DG' uses a rate code with cells active in different contexts overlapping considerably, whereas in CA3′ there is little overlap between those active in different but similar contexts. Leutgeb et al. .The proportion of sampled cells firing during tests in one of two familiar contexts in rat dentate has been reported to be about a third that in CA3 . How might this number be estimated on the fly without extensive prior sampling of a context? (3) It seems not unlikely that sampling slows or stops during freezing. If so, it would greatly affect BACON's behavior and needs to be considered as part of a theory of sampling. (4) Random sampling is a useful simplifying assumption, but some attributes are surely more salient than others. This ultimately should be incorporated into a model such as this. (5) BACON assumes that existing representations are activated serially and evaluated for validity as they become active; a more sophisticated algorithm that can compare validities of multiple attributes in parallel would produce better performance. (6) Extinction, which we chose to ignore, must be taken into account. It will be introduced into the alogrithm at a later time by assuming, as done in the above-mentioned model of the amygdala, that extinction occurs because unreinforced fear responses cause potentiation at synapses between active CA3′ neurons and amygdala interneurons that inhibit BACON's fear-producing neurons.A number of simplifying assumptions were made during the design of BACON, and ways of moving beyond them should be explored in future work. Some matters especially needing consideration are these: (1) A theory of sampling. How does attribute sampling vary over time; does it slow as the set of attributes so-far observed during a session becomes more complete? (2). We assumed that all contexts have the same number of attributes. Ways of dealing with cases where this is an implausible assumption are needed. Weight of Evidence calculations depend on the total number of attributes available for sampling in a situation . Overall, we believe that the approach taken provides insight into both context fear learning mechanisms and hippocampal function in general.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


There has been increased detection of incidental AVMs as result of the frequent use of advanced imaging techniques. The natural history of AVM is poorly understood and its management is controversial. This review provides an overview of the epidemiology, pathophysiology, natural history, clinical presentation, diagnosis, and management of AVMs. The authors discussed the imaging techniques available for detecting AVMs with regard to the advantages and disadvantages of each imaging modality. Furthermore, this review paper discusses the factors that must be considered for the most appropriate management strategy (based on the current evidence in the literature) and the risks and benefits of each management option. AVMs are abnormalities of the intracranial vessels that constitute a connection between the arterial and venous systems and lack an intervening capillary bed. Hemorrhagic presentation of AVM is associated with significant morbidity and mortality; it is an independent predictor of future hemorrhage. The gold standard for diagnosis of AVM is cerebral angiography. However, the evolution of noninvasive imaging techniques has led to the increased diagnosis of unruptured AVM which now presents with new challenges with regard to their management. This review paper provides a comprehensive review of the literature with presentation of the risks and benefits of the different management options available for AVM such as medical management, microsurgical resection, stereotactic radiotherapy, and endovascular embolization. Furthermore, the clinical presentation of patients with AVM and how it relates to the preferred management option are discussed in detail.Approximately 2% of AVMs are multiple and the remainder are solitary . AccordiAVMs have three components: feeding arteries, nidus, and draining veins . The groAVMs are congenital lesions that occur sporadically. The familial incidence of brain AVMs is rare, and only a few reported cases in the literature; however there is an association with other abnormalities like Osler-Weber-Rendu disease and Sturge-Weber syndrome , 9. CereThe natural history of asymptomatic brain AVMs remains poorly understood and conflicting information can be found on symptomatic lesions in the literature. Although scientists have not reliably identified anatomic predictors, spontaneous obliteration may be more likely to occur in small AVMs (less than 2.5 cm) that present with hemorrhage and have fewer arterial feeders . This phCerebral AVMs may present with intracranial hemorrhage, seizures, headaches, and long-term disability; the most common presenting symptoms are hemorrhage and seizures .The annual incidence of hemorrhage of unruptured and untreated brain AVMs is of 2% to 4% with approximately 38% to 71% of patients with brain AVMs presenting with intracranial hemorrhage . There aThere is data to suggest that hemorrhagic presentation is a significant independent predictor of future hemorrhage. Ondra and colleagues  over a 2Other potential risk factors for hemorrhage include (1) AVM with exclusively deep venous drainage , (2) AVM associated with aneurysms, (3) AVMs that are deep in location, and (4) AVM that is infratentorial in location . Brain ASeizures occur in about 18% to 40% of brain AVMs with favorable response to treatment with antiepileptic drugs , 25. TheHeadaches occur in approximately 5% to 14% of patients with brain AVMs and these headaches are not distinctive. They can be unilateral or bilateral and can have migrainous features with and without aura , 26. CurFocal neurologic deficits (FNDs) occur in 1% to 40% of patients with brain AVMs . Only 5%Conventional cerebral angiography is the gold standard in the evaluation of AVM angioarchitecture, and it shows the following essential features: the feeding arteries, location of nidus, draining veins, morphology, presence, and location of associated aneurysms, venous varices, and vasculopathic stenotic segments on arteries and veins. These features are important because they are commonly used for treatment planning . One of Other imaging modalities which are often the initial studies used to evaluate symptoms that are not specific to AVMs include CT, CT angiography, MRI, and magnetic resonance angiography. However, these imaging techniques are limited in their sensitivity and ability to provide detailed imaging of AVM architecture . Each imAn important factor that must be considered during the treatment decision-making process is to compare the risks of all treatment modalities against the natural history risks of AVMs. Management of cerebral AVMs includes observation with medical management, microsurgical resection, stereotactic radiotherapy, and endovascular embolization. Invasive treatment modalities are the reasonable choice for ruptured cerebral AVMs due to the high rate of morbidity and mortality, and the goal of treatment is eradication of the AVM. The factors that dictate treatment options  are operator skill, AVM size and location, surgical or endovascular accessibility, venous drainage, and presence of high-risk features, such as a feeding artery aneurysm .However, the appropriate treatment modalities for unruptured AVMs present a challenging clinical dilemma because of a poorly defined natural history and the seemingly low annual hemorrhage rates. This clinical conundrum led to the development of ARUBA which aims to compare the natural history with modern multimodal therapy. ARUBA  was the first randomized controlled trial to evaluate surgical intervention versus medical management for unruptured cerebral AVMs. However, errors in study design, execution, short length of follow-up, and a relative lack of information regarding the treatment arm and the enrollment process invalidate the authors' conclusions .Conservative treatment is considered for management of asymptomatic AVMs. Furthermore, it may include management of associated symptoms, general medical care, and surveillance imaging of an AVM. Time intervals for surveillance imaging are not well defined and may include MRI brain imaging annually or biennially. Specific medical care may include management of hypertension, headache, and seizures. Similar outcomes in seizure frequency have been reported in an observational study comparing conservative management and AVM treatment .In 1986, Spetzler and Martin introduced a grading system for AVMs based on the nidus size, location in relation to eloquent cortex, and venous drainage pattern see ; site inThe cure of AVM in adults is definitive with complete microsurgical resection and angiographic confirmation of obliteration. However, AVMs in children are more dynamic and may have the ability to regenerate after negative angiographic studies .Radiosurgery involves the delivery of localized high-dose radiation to the AVM to induce a vascular injury, which leads to gradual sclerosis of the blood vessels with eventual obliteration over a period of 2 to 3 years. Successful treatment with radiosurgery depends on AVM size, grade, location, angioarchitecture, density of the nidus, and radiation dosage. AVMs smaller than 3.5 cm are ideal for obliteration . The timHowever, this is less favorable with microsurgical resection. About 2 to 5 years after radiosurgery, the risk of hemorrhage is slightly higher at 5.0% per year but not significantly different from the natural history of AVMs. However, it should be noted that Pikus and colleagues demonstrated that microsurgically treated grade I to III AVMs had higher incidence of obliteration with statistically significant fewer postoperative hemorrhages, neurological deficits, and deaths when compared with stereotactic radiosurgery . A multiThe advantages of radiosurgery include a noninvasive therapy and reasonable obliteration rates. The disadvantages of radiosurgery include the risk of bleeding during the latency of 1 to 2 years, neurologic deficits from edema and necrosis of normal brain tissue, and individual sensitivity to radiation and unknown long-term outcome.Endovascular treatment of brain AVMs involves the delivery of liquid embolics, such as n-butyl cyanoacrylate and ethylene vinyl alcohol copolymer (Onyx) and platinum embolic coils via superselective catheterization with flow-guided ultrathin microcatheters. Often times, it is performed as preoperative embolization to surgical resection or in conjunction with stereotactic radiotherapy. Preoperative embolization can reduce the size of an AVM for microsurgical excision, and it has been shown to have acceptable rates of clinically significant complications (approximately 6.5%) .Embolization may be performed as an adjunctive treatment to reduce the size of the AVM before radiosurgery. In certain cases, small malformations may be completely obliterated by embolization alone and large AVMs may undergo near-complete obliteration. Furthermore, palliative embolization may be used in selected cases to stabilize progression of neurologic deficits or attempt seizure control in cases where AVMs are not amenable to microsurgical excision or radiotherapy.The advantages of endovascular therapy include a minimally invasive approach, possible immediate occlusion, and intraprocedure angiographic evaluation. The disadvantages of endovascular therapy include incomplete embolization, unintended vessel embolization, intracranial hemorrhage, and normal perfusion pressure breakthrough, leading to edema or hemorrhage .The increasing use of advance imaging techniques will increase the incidence of asymptomatic AVMs. At the present moment, we do not fully understand the natural history of AVMs to precisely predict which AVMs will likely bleed and what the most appropriate optimal treatment option will be, single or multimodal therapy. In the future, we certainly need well designed randomized controlled trials to compare different treatment modalities and their outcomes.