Gabbro- and alkaline peridotite- aquifers harbor more diverse communities and contain abundant microbial taxa affiliated with Nitrospira, Nitrosospharaceae, OP3, Parvarcheota, and OP1 order Acetothermales. Wells that sit at the contact between gabbro and peridotite host microbial communities distinct from all other fluid types, with an enrichment in betaproteobacterial taxa. Together the taxonomic information and geochemical data suggest that several metabolisms may be operative in subsurface fluids, including methanogenesis, acetogenesis, and fermentation, as well as the oxidation of methane, hydrogen and small molecular weight organic acids utilizing nitrate and sulfate as electron acceptors. Dynamic nitrogen cycling may be especially prevalent in gabbro and alkaline peridotite fluids. These data suggest water-rock reaction, as controlled by lithology and hydrogeology, constrains the distribution of life in terrestrial ophiolites.Microbial abundance and diversity in deep subsurface environments is dependent upon the availability of energy and carbon. However, supplies of oxidants and reductants capable of sustaining life within mafic and ultramafic continental aquifers undergoing low-temperature water-rock reaction are relatively unknown. We conducted an extensive analysis of the geochemistry and microbial communities recovered from fluids sampled from boreholes hosted in peridotite and gabbro in the Tayin block of the Samail Ophiolite in the Sultanate of Oman. The geochemical compositions of subsurface fluids in the ophiolite are highly variable, reflecting differences in host rock composition and the extent of fluid-rock interaction. Principal component analysis of fluid geochemistry and geologic context indicate the presence of at least four fluid types in the Samail Ophiolite  that vary strongly in pH and the concentrations of H Over the course of these three field seasons, 20 water samples, including particulates and dissolved gases, were collected from a total of 12 wells. Geographic coordinates, elevations, and depths of boreholes are reported in Table A submersible pump was utilized to collect subsurface fluids from boreholes for geochemical and microbiological analyses. The depth of the water table and depth of pumping for sample retrieval are reported in Table 2 to prevent microbial modification of samples post-collection. Fluids (5–20 L) for biomass recovery were pumped and filtered through 0.2 micron Millipore polycarbonate inline filters to concentrate cells for DNA extraction. Filters were placed in sterile cryovials, transported frozen in liquid nitrogen, and stored in a −80°C freezer until extraction.Redox sensitive species  were measured in the field using Hach water chemistry test ampules  with a portable Hach DR/890 colorimeter . Numerous subsamples of deep fluids were also prepared in-field for laboratory-based geochemical analysis. Aliquots of fluid were collected in sterile syringes, filtered through a 0.22 micron filter, and injected into nitrogen-purged or evacuated vials with butyl stoppers for headspace gas analysis. Fluids for organic acid measurements were filtered through a 0.22 micron filter to remove microbial cells. The filters were pre-purged with fluid before sample collection and the filtrate was collected in ashed, organic-free vials capped with silicon septa. All vials were acid washed, autoclaved, and muffled at 400°C prior to field work. Samples for ICP analysis of major cations and trace elements were filtered with 0.2 micron Millipore filters and acidified in the field with concentrated nitric acid to a pH <2, whereas aliquots for IC analysis of anions were filtered, but preserved unacidified. Samples for dissolved inorganic carbon measurements were poisoned with HgCl+, Mg2+, Ca2+, Al3+) were analyzed using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) on a Thermoscientific X Series 2 spectrometer . Trace element  measurements for 2014 and 2015 fluid samples were conducted using ICP-MS on a Perkin-Elmer Elan DRC-E mass spectrometer according to the U.S. Environmental Protection Agency (EPA) method 6020 . In 2016, only Ni, Cu, and Cr were measured using ICP-MS as described above for major cation analysis on the X Series 2 spectrometer . Silica concentrations were determined using Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) on a 3410 Applied Research Laboratories instrument following EPA method 6010 ; for 2016 samples, the American Standard Test Method D 859-00 for colorometric measurement of silica was utilized with a Beckman Coulter DU 730 UV/Vis spectrophotometer . Major anions . Samples for organic acid measurements were sent to NASA Ames Research Center for measurement on a Shimadzu Prominence LC20AT high-performance liquid chromatograph (HPLC) equipped with a SPD-M20A photodiodearray detector .The concentrations of hydrogen and methane gas exsolved from well fluids were determined using a SRI 8610C gas chromatograph (GC) with a 2 m by 1 mm ID micropacked ShinCarbon ST column with nitrogen as the carrier gas. 0.5 mL of headspace gas from butyl stopper-capped fluid samples were injected into the sampling port on the GC for analysis. Hydrogen and methane were measured concurrently using a thermal conductivity detector (TCD) and a flame ionization detector (FID) respectively .https://github.com/leffj/helper-code-for-uparse). Merging, quality filtering, and phylotype clustering were conducted using the UPARSE pipeline  according to the manufacturer's instructions. PCR amplification of the V4-V5 region of the 16S rRNA gene was performed in triplicate using barcoded 515F and 806R primers that contained the appropriate Illumina adapters and linkers according to the protocol described by Caporaso et al. . Triplice Edgar, . Reads wAll multivariate statistical analyses were performed in R  of the geochemical parameters measured in all three field seasons Figure . CalculaThe PCA reveals a strong partitioning between the 20 fluid chemistries on the biplot. Notably, we can distinguish between two geochemical subgroups of peridotite-hosted fluids, which we classify as “hyperalkaline” pH >10) or “alkaline” (pH 8–10) for subsequent microbial community analysis. Hyperalkaline peridotite fluids plot in the right quadrants of the PCA and are characterized by high dissolved hydrogen, methane, and calcium concentrations, and high pH. These fluids are enriched in trace elements such as nickel and depleted in magnesium, sulfate, nitrate, and silica. Redox potential is also very low in these samples. Although not pictured due to the lack of 2016 DIC data, hyperalkaline fluids are all limited in DIC  phylotypes were detected in one or more wells Figure . These 3Methanobacteria, constituting 99.1% of the total archaeal reads and 28.0% of total reads for this well. The genus Methanobacteria was detected in a total of 16 samples, but was only in high relative abundance (>3%) in two other samples- the crust/mantle contact well WAB188 and the hyperalkaline peridotite well WAB56, both from the 2015 field season. Sequences affiliated with the phyla Thaumarchaeota and Parvarchaea dominated the archaeal populations in all other wells.Biomass sampled from all wells yielded a greater number of bacterial reads than archaeal reads Table . ArchaeaMeiothermus , Acinetobacter (6.62%), Thermodesulfovibrionaceae (5.33%), and Candidate Phylum OP1 class MSBL6 (4.94%). Also common were phylum OP1 Candidatus Aceothermum (2.53%), Cupriavidus (2.48%), Dehalococcoidetes (2.15%), Nitrospira (2.14%), and Rhodocyclaceae . With the exception of Acinetobacter, most of these taxa were only abundant in a few individual wells. Microbial community composition was highly variable across wells. Only phylotypes affiliated with candidate phyla OD1, GAL15, and OP1, as well Betaproteobacteria belonging to the family Comamonadaceae were abundant across all samples.The most abundant bacterial taxa were r = 0.43, p < 0.001). However, the multi-collinearity of geochemical parameters precludes meaningful statistical correlation of microbial community composition with any one geochemical parameter , Thaumarcheota belonging to the family Nitrososphaeraceae, candidate phyla OP3 and Parvarcheota, as well as OP1 order Acetothermales.Hyperalkaline peridotite wells exhibit microbial communities dominated primarily by taxa affiliated with the family Thermodesulfovibrionaceae, candidate phylum OP1 class MSBL6, and The chemistry of subsurface fluids in the Samail Ophiolite reflects both differences in host rock as well as hydrologic context—i.e., the extent of equilibration with the host rock or atmosphere and the potential for mixing with other fluids. Groundwater flow in this region follows the local topography from mantle rocks exposed in sharp-peaked mountainous catchments to crustal gabbros downgradient in rounded hills of more moderate relief  are likely sourced from near-surface flow in peridotite-hosted aquifers open to the atmosphere. These wells are characterized by high elevations (>650 m above sea level), and thus expectedly only tap into shallow, meteoric-sourced fluids near the zone of recharge. The high redox potential and DIC concentrations, as well as low salinity and trace metal content of alkaline peridotite fluids also support the theory of a short residence time and contact with the atmosphere. Surficial aqueous alteration of the host rock would lead to the dissolution of magnesium-bearing phases in peridotite, consequently increasing pH and converting dissolved carbon dioxide to bicarbonate  are similar to those of alkaline-peridotite fluids, implying these fluids also have reacted at a shallow depth while in contact with the atmosphere. However, gabbro-hosted fluids exhibit an order of magnitude higher concentrations of both sodium and chloride, as well as increased concentrations of calcium, silica, aluminum, and trace elements. The increased concentration of calcium and silica in gabbro-hosted compared to alkaline peridotite-hosted aquifers is consistent with previous studies of crustal fluids and likely reflects the mineral composition of gabbros, i.e., more pyroxene and plagioclase feldspar than olivine and serpentine Stanger, . The higThe high conductivity of hyperalkaline peridotite-hosted fluids observed in this study  implies extensive water/rock reaction, and the low measured redox potential in combination with the presence of dissolved hydrogen and methane gases is also consistent with the idea that these fluids are the product of low-temperature serpentinization , multiple r2 = 0.6604, F-statistic = 35.01, p < 0.001; Figure Serpentinization also yields a unique set of geochemical conditions that organisms inhabiting reacted fluids must adapt to: the most evident consequence being the increase in pH of reacted fluids. The pH of fluids has an apparent negative correlation with microbial diversity as measured by OTU richness , and the maximum measured concentrations were up to 2.88 mM, more than twice the concentration observed in seeps at the Tablelands Ophiolite known to support hydrogen-metabolizing life  in the fluids, and ample ferric iron is stored within secondary minerals as the byproduct of serpentinization. Such Fe(III) in serpentine and Fe(III) in magnetite in near-surface rocks  pathway has been proposed as a putative metabolism for members of candidate phylum OP1, or Meiothermus is an aerobic heterotrophic genus belonging to the Deinococcus/Thermus clade  than in hyperalkaline fluids. While the sources of these electron acceptors are enigmatic, the depletion of these e-acceptors in deeper fluids can likely be attributed to their consumption by nitrogen and sulfur-cycling microorganisms in the upper aquifer.Potential electron donors in alkaline peridotite and gabbro fluids with no detected hydrogen or methane are more enigmatic. Mineral sources may provide a source of energy in the form of ferrous iron or ammonium  and some strains are highly resistant to heavy metals  bacteria that derive energy for growth through the conversion of ammonium and nitrite into nitrogen gas under anoxic conditions  minerals. The appreciable concentrations of electron acceptors in all fluids suggests that the serpentinized subsurface may not be as limited in oxidants as previously thought. For example, our data suggest that sulfate is a critical electron acceptor for sustaining subsurface microbial life within the ophiolite. Active nitrogen cycling also occurs, and processes such as ammonium oxidation, nitrite oxidation, and nitrate reduction may be strongly controlled by the hydrologic regime.Meiothermus, Thermodesulfovibrionaceae, and candidate phylum OP1 class MSBL6. However, we also detect abundant Comamonadaceae, including Hydrogenophaga, as well as Firmicutes, Psuedomonadaceae, and Methanobacterium, indicating a core similarity to other deep subsurface or serpentinizing settings. From these taxonomic affiliations, we infer methanogenesis, acetogenesis, and fermentation are dominant metabolisms in highly reacted fluids. Hydrogen metabolism is likely also coupled to several strong oxidants such as sulfate, Fe(III)-minerals, and nitrate.Comparisons of the microbial community structure and diversity of deep gabbro- and peridotite-hosted fluids in Oman offers a framework for differentiating distinct subsurface microbial biomes. We found that the diversity of detected microbial communities varies considerably with fluid type. pH is a predictor for the richness of microbial communities. Microbial communities in reacted, hyperalkaline peridotite fluids are characterized by low richness; these communities differ from those previously detected at hyperalkaline springs from ophiolite systems worldwide and are comprised primarily of Nitrospira, suggesting nitrogen cycling may be particularly active in upper aquifer fluids. We observe a unique community inhabiting wells at the contact between gabbro and peridotite; these communities do not host a consistent, core microbial community, but are particularly enriched in Betaproteobacteria. We hypothesize these contact zones represent areas of fluid mixing, enhancing chemical disequilibrium. The consistent parsing of microbial communities as a function of fluid type is likely driven by differential energy availability and aqueous geochemistry  that results from fundamental differences in both host rock lithology and the extent of water-rock reaction. Thus, identifying the origin and reaction paths of fluids, as well as the source and rates of consumption of oxidants and reductants in such systems, is integral to understanding the limits to life in the subsurface of terrestrial ophiolites.Gabbro and alkaline peridotite fluids host relatively rich microbial communities dominated by candidate phyla as well as phylotypes affiliated with nitrification, including Nitrosospharaceae and http://www.omandrilling.ac.uk/), which will provide a tractable experimental system for forthcoming subsurface biosphere research.This work provides an important framework for interpreting the habitability of terrestrial serpentinizing environments, and raises many additional questions. These communities should be targeted for physiological and field-based studies to identify the energetic costs and mechanisms of organisms capable of surviving under extreme energy limitation in rock-hosted environments. Further research is necessary to quantify the biomass residing in this ecosystem and to determine how the rates of key metabolic processes are distributed across geochemical gradients. Thermodynamic modeling of energy densities in this system could provide testable insights into the potential activity and metabolisms of this ecosystem, particularly if combined with genomic data. This work would be especially beneficial in determining the efficiency and prevalence of heterotrophic vs. chemoautotrophic metabolisms that may operate in this environment. Notably, both organic and inorganic electron donors are available, even in deep hyperalkaline fluids. Elucidating how the coupled hydrology and water/rock reactions generate the flux of electron donors and acceptors in this system is also essential to developing an understanding of the subsurface microbial ecology of terrestrial serpentinites. Isotopic measurements of these chemical constituents and their possible sources could resolve the question of their origin, further constraining how the distribution of life in this subsurface ecosystem varies across geologic context and hydrologic regime. All of these efforts will be greatly aided by increased access to fluids and their host rocks for repeated biogeochemical and microbiological sampling, monitoring, and experimentation through the International Continental Drilling Program (ICDP) project in Oman , with supporting geochemical work funded through the Department of Energy (DE-SC0006886). We would like to thank the Alfred P. Sloan Foundation Grant 2014-3-01 to PK for additional support for field logistics associated with this work.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.


The stimulant methylphenidate (MPH) and the nonstimulant atomoxetine (ATX) are the most commonly-prescribed pharmacological treatments for attention deficit/hyperactivity disorder (ADHD). However, the drug-specific mechanism of action on brain function in ADHD patients is not well known. This study examined differences in prefrontal hemodynamic activity between MPH and ATX in children with ADHD as measured by near-infrared spectroscopy (NIRS) using the Stroop color-word task.Thirty children with ADHD participated in the present study. We used 24-channel NIRS (ETG-4000) to measure the relative concentrations of oxyhemoglobin in the frontal lobes of participants in the drug-naïve condition and those who had received MPH (n = 16) or ATX (n = 14) for 12 weeks. Measurements were conducted every 0.1 s during the Stroop color-word task. We used the ADHD RS-IV-J (Home Version) to evaluate ADHD symptoms.Treatment with either MPH or ATX significantly reduced ADHD symptoms, as measured by the ADHD RS-IV-J, and improved performance on the Stroop color-word task in terms of number of correct words. We found significantly higher levels of oxyhemoglobin changes in the prefrontal cortex of participants in the ATX condition compared with the values seen at baseline (pre-ATX). In contrast, we found no oxyhemoglobin changes between pre- and post-treatment with MPH.The present study suggests that MPH and ATX have differential effects on prefrontal hemodynamic activity in children with ADHD. Attention-deficit/hyperactivity disorder (ADHD) is one of the most commonly diagnosed neurodevelopmental disorders in children with lifelong deficits in a wide range of executive functions . ADHD syMethylphenidate acts as an indirect DA agonist, inhibiting DA reuptake by occupying the DA transporter . MPH hasNear-infrared spectroscopy (NIRS) enables the noninvasive detection of neural activity near the surface of the brain using near-infrared light , 15. It Hemoglobin ([deoxy-Hb]) concentrations in micro-blood vessels on the brain surface. Local increases in [oxy-Hb] and decreases in [deoxy-Hb] are indicators of cortical activity , 16. In In pediatric ADHD, reduced prefrontal hemodynamic response has been measured by NIRS , 29, 30.Thirty patients aged 6–14 years and diagnosed with ADHD according to the DSM-5 criteria  participWe used NIRS to measure the relative concentrations of oxy-Hb in participants in the drug-naïve condition (pre-treatment) and after 12 weeks of treatment with either osmotically released MPH (n = 16) or ATX (n = 14) (post-treatment). The participants were assigned either MPH or ATX by the decision of an experienced pediatric psychiatrist. All measurements were conducted at the same time of day (10.00–11.00 h). All the participants were MPH and ATX naïve and started to take MPH 18 mg/day or ATX 0.5 mg/kg/day in the morning, respectively. They were titrated up as needed to the lowest effective dose by the decision of an experienced pediatric psychiatrist every 2 weeks. The mean dose of MPH was 0.87 mg/kg (SD = 0.23), and the mean dose of ATX was 1.30 mg/kg (SD = 0.44). The characteristics of the participants are shown in Table We used the ADHD Rating Scale-IV-Japanese version (ADHD RS-IV-J) (Home Version)  to evaluThe traditional Stroop task was combined with the word-reading task, incongruent color-naming task, and the color-naming task. However, we reconstructed the Stroop task according to previously described methods . The StrStroop color-word task number of correct answers first time (SCWC-1), second time (SCWC-2), and third time (SCWC-3). Examiners who were blind to the diagnoses of the participants administered the Stroop color-word task. The Stroop task used in this study was different from the traditional Stroop task. We made the Stroop color-word task simple because the participants were school-aged children. Furthermore, we excluded the color-naming task  because we wanted to have only two tasks (baseline task and activation task) for our NIRS study.2. The lowest probes were positioned along the Fp1–Fp2 line according to the international 10/20 system commonly used in electroencephalography. The correspondence between the probe positions and the measurement points in the cerebral cortex were confirmed by superimposing the probe positions onto a three-dimensionally reconstructed cerebral cortex of a representative participant in the control group, obtained via MRI . We measured the absorption of two wavelengths of near-infrared light (760 and 840 nm). [Oxy-Hb] was calculated as previously described . The int2) test to examine group differences for categorical variables (e.g. gender). Clinical variables with a normal distribution were compared using Student’s t tests. Correlations between SCWC and characteristics of the subjects were tested with Spearman’s correlation test. For statistical comparison of the participant characteristics between the pre- and post-treatment conditions, we used a two-tailed paired t test. Specifically, we compared oxy-Hb changes between the pre- and post-treatment conditions. To conduct a more detailed comparison of oxy-Hb changes along the time course of the task, we used MATLAB 6.5.2  and Topo Signal Processing type-G version 2.05 .We used the Chi square  × condition  interactions. The threshold for statistical significance was set at p < 0.05. Bonferroni-adjusted p values are reported (i.e. corrected for multiple comparisons). We used PASW Statistics18.0J for Windows  for statistical analyses.The demographic characteristics of the study participants are presented in Table Because the MPH and ATX groups varied considerably in terms of SCWC-1 SCWC-2 scores, we calculated Spearman’s correlations for the SCWC scores, age, FIQ, and ADHD-RS-IV-J, as shown in Table Both treatments were associated with statistically significant improvements in terms of both ADHD-RS-IV-J scores and SCWC scores, as shown in Table We calculated the grand average waveforms of [oxy-Hb] concentration changes during the Stroop color-word task in the pre- and post-treatment condition Figs. , 3. Fig.Channel 21 showed significant treatment-by-condition interactions . However, there were no main effects for either treatment or condition on channel 21 . We did not find any differences in mean [oxy-Hb] measurements between the pre-ATX and the pre-MPH  on this channel. However, the mean oxy-Hb measurement for channel 21 was significantly larger for post-ATX relative to post-MPH .We conducted Spearman’s rank correlation analyses between hemodynamic change in channel 21 with scores of SCWC and ADHD-RS-IV-J scores, shown in Table To our knowledge, this is the first NIRS study to compare the effectiveness of MPH with ATX directly in children with ADHD by measuring hemodynamic responses during the Stroop color-word task. ATX significantly increased activation in the prefrontal cortex, especially in left lateral frontal pole cortex (FPC), after 12 weeks of administration. MPH did not increase activation in the prefrontal cortex, but it did make comparable improvements in terms of ADHD symptoms and Stroop color-word task performance to those seen in ATX.Some studies have referred indirectly to differences in the neurobiological actions between MPH and ATX. Event-related potential studies of oddball tasks in pediatric ADHD have shown that MPH can normalize low P300 or mismatch negativity amplitudes , while AVolkow et al. , 49 founIncreases in left lateral FPC activity were observed after ATX treatment in our study. However, we found no significant correlations between the hemodynamic changes in this area and degree of the clinical improvements. The FPC is the most anterior part of the cerebral cortex, and has reciprocal connections with most prefrontal areas , 66. TsuThe results of the present study suggest that multi-channel NIRS systems may have potential in the pharmacotherapeutic evaluation in children with ADHD for clinical practice. It is very significant for patients that an effect of the pharmacotherapy is visualized. In the future, it is need to predict the effect of the pharmacotherapy using the NIRS for clinical practice.The present study has several potential limitations. First, methodological limitations include the relatively small number of participants, non-randomised study, and lack of a double-blind, placebo-controlled design. At baseline, the ATX group had higher mean SCWC1 and SCWC2 scores than the MPH group. Although scores were not correlated with degree of clinical severity with ADHD-RS, the two groups were not quite entirely equivalent in their characteristics. Future work seeking to compare MPH, ATX and/or placebo should consider a double-blind randomized or crossover design with larger samples. Second, we had no healthy control as a comparison cohort. Our study showed that ATX significantly increased activation in channel 21. In one previous NIRS study using the Stroop, Negoro et al. reported a lower increase of oxy-changes in channels 8, 18, 19, 21, and 22 in individuals with child ADHD compared with controls . ConsideIn conclusion, this is the first NIRS study using the Stroop interference task to examine how the pharmacological mechanisms of action differ between MPH and ATX. Findings suggest that effective treatment with MPH and ATX is produced by distinct mechanisms in frontal regions.


Attention-deficit hyperactivity disorder (ADHD) has historically been considered a disorder of childhood and adolescence. However, it is now recognized that ADHD symptoms persist into adulthood in up to 60% of individuals. Some of the cognitive symptoms that characterize ADHD  may closely resemble symptoms of prodromal dementia, also often referred to as mild cognitive impairment (MCI), particularly in patients over age 50. In addition to the overlap in cognitive symptoms, adults with ADHD and those with MCI may also share a number of behavioral and psychiatric symptoms, including sleep disturbances, depression, and anxiety. As a result, both syndromes may be difficult to distinguish clinically in older patients, particularly those who present to memory clinics with subjective cognitive complaints and fear the onset of a neurodegenerative process: is it ADHD, MCI, or both? Currently, it is unclear whether ADHD is associated with incipient dementia or is being misdiagnosed as MCI due to symptom overlap, as there exist data supporting either possibility. Here, we aim to elucidate this issue by outlining three hypothetical ways in which ADHD and MCI might relate to each other, providing an overview of the evidence relevant to each hypothesis, and delineating areas for future research. This is a question of considerable importance, with implications for improved diagnostic specificity of early dementia, improved accuracy of disease prevalence estimates, and better identification of individuals for targeted treatment. Attention-deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder characterized by cognitive deficits (inability to sustain attention) and/or behavioral disturbances (inability to regulate motor behavior). The symptoms emerge before age 12 and disrupt participation in schoolwork, chores or interpersonal relationships , these are thought to arise from compromised aspects of frontal lobe functioning. Fronto-striatal, frontal-temporo-parietal, and fronto-cerebellar networks have been documented as underdeveloped in ADHD compared to age-matched controls . Rather, these models are intended to complement each other by conceptually illustrating different aspects of the possible relationship between ADHD and MCI, which could guide future experiments aimed at untangling the possible links between the disorders. Lastly, as the specific etiologies of these highly heterogeneous conditions remain unknown, many of the elements presented within these frameworks are speculative and will need to be tested directly.Currently, the relationship between adult ADHD and MCI remains unclear. Updating and building upon Ivanchak and Jicha's previous report  and that could conceivably be secondary to other disease processes. ADHD symptoms are often measured in research studies using self- or informant-report questionnaires, such as the Conners' Adult ADHD Rating Scales  but no functional impairment, whereas dementia refers to a later point at which there are cognitive and functional impairments  has been used to refer to a system of cognitive processes involving the activation and controlled maintenance of goal-directed thought. In this light, attention falls under the scope of executive functions. These processes are reflected in tasks such as sustained, selective, focused and divided attention , which is a protein involved in neural growth and function  and amyloid-β biology (into late adulthood). The possibility that changes in amyloid-β biology may constitute a pathophysiological link between ADHD symptoms and AD may be supported by several lines of behavioral evidence. First, decreased amyloid-β 42 levels in the cerebrospinal fluid, observed in preclinical AD . Their mediating effects on MCI in adults with ADHD are thus likely highly complex and multifactorial.ADHD may possibly mimic the cognitive symptoms of MCI without being associated with incipient dementia. Experts in the field of dementia have urged emerging research to distinguish prodromal dementia syndromes from non-degenerative cognitive impairment in order to allow for the creation of appropriate treatment options   is the hypothesized mechanism leading to episodic memory impairment in AD  and comparing the frequencies of these pathologies between individuals with and without a history of ADHD. A certain amount of these pathologies can be expected within the context of normal aging . In the field of dementia, such studies have been instrumental in establishing gold standards for diagnosis  and psychiatric comorbidities . This has led to speculation that ADHD may be an incipient form of dementia, perhaps related to vascular or Lewy body pathology, through shared pathological mechanisms or via an unrelated mediator. Although there is a small number of intriguing findings that support a pathophysiological connection between ADHD and dementia, the bulk of the evidence presented in our review suggests that ADHD is a neurodevelopmental process fundamentally unrelated to MCI, and that any mechanistic link between the disorders is likely attributable to health-compromising mediators common in the ADHD population. Much of the diagnostic confusion that has been reported in memory clinics, including our own, presumably stems from phenotypical similarities between both syndromes. Of course, the possibilities outlined above are not mutually exclusive, and in some cases ADHD and MCI may overlap stochastically even without shared pathological pathways or mediators. Nevertheless, the hypotheses outlined above will need to be formally tested and replicated by independent research groups in order to fully ascertain the nature of relationship between these two conditions, and to determine whether the extent to which there exists phenotypical heterogeneity and possible subtypes in each syndrome.Regardless of whether or not ADHD is a stage within a neurodegenerative process, current criteria for diagnosing MCI or dementia may not be appropriate or valid in individuals with a premorbid history of attentional and/or hyperactive difficulties. One core criterion for the diagnosis of a neurocognitive disorder is the need to establish “substantial impairment in cognitive performance, preferably documented using standardized neuropsychological testing” (American Psychiatric Association, One major inescapable limitation of research in the area of adult ADHD is recall bias. Currently, a retrospective diagnosis of ADHD in adults relies on the presence of inattention and hyperactivity symptoms in childhood (i.e., before age 12; American Psychiatric Association, Nonetheless, informant reports may also be biased, and retrospective recall is not ideal for establishing diagnosis. At this time, it may be worthwhile for the medical community to consider the formulation of criteria for current ADHD symptoms specific to adults and seniors. In its most recent revision of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5; American Psychiatric Association, The present paper extends previous work beyond a descriptive analysis of the overlapping features of both syndromes, and provides a framework that can guide the design of research studies in this area. Further work should include syndromatic as well as symptomatic cases of ADHD, prospective longitudinal cohort studies and, eventually, autopsy studies in order to broaden our current knowledge of this under-studied area of adult neuropsychology. This is crucial for several reasons. First, improved accuracy of disease incidence and prevalence rate estimates will have important socio-economic impacts, both direct and indirect (Bolea et al., BC and DB conceived the question of interest, conceptualized and developed the models, performed the literature review and wrote the manuscript. DS and SB made substantial contributions to the conception and design of the models, and revised the manuscript critically for important intellectual content. All authors commented on the manuscript at all stages and consent to their names appearing on it.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.


Introduction: Attention-deficit hyperactivity disorder (ADHD) is one of the most frequent neurodevelopmental disorders in children and tends to persist into adulthood. Evidence from neuropsychological, neuroimaging, and electrophysiological studies indicates that alterations of error processing are core symptoms in children and adolescents with ADHD. To test whether adults with ADHD show persisting deficits and compensatory processes, we investigated performance monitoring during stimulus-evaluation and response-selection, with a focus on errors, as well as within-group correlations with symptom scores.Methods: Fifty-five participants (27 ADHD and 28 controls) aged 19–55 years performed a modified flanker task during EEG recording with 64 electrodes, and the ADHD and control groups were compared on measures of behavioral task performance, event-related potentials of performance monitoring , and error processing . Adult ADHD Self-Report Scale (ASRS) was used to assess ADHD symptom load.Results: Adults with ADHD showed higher error rates in incompatible trials, and these error rates correlated positively with the ASRS scores. Also, we observed lower P3 amplitudes in incompatible trials, which were inversely correlated with symptom load in the ADHD group. Adults with ADHD also displayed reduced error-related ERN and Pe amplitudes. There were no significant differences in reaction time (RT) and RT variability between the two groups.Conclusion: Our findings show deviations of electrophysiological measures, suggesting reduced effortful engagement of attentional and error-monitoring processes in adults with ADHD. Associations between ADHD symptom scores, event-related potential amplitudes, and poorer task performance in the ADHD group further support this notion. Attention-deficit hyperactivity disorder (ADHD) is a frequent neurodevelopmental disorder in children, and recent research has shown that ADHD symptoms persist into adulthood in about 15–65% of childhood cases , with a The ability to dynamically adjust attention and behavior to situational demands, hence to monitor performance, is a crucial part of adequate daily functioning , and reqSeveral studies have shown impairments in performance monitoring tasks in children and adults with ADHD, and concomitant changes in the fronto-striatal network. Considering electrophysiology, some studies point to smaller ERN amplitudes in children with ADHD , as wellA recent small-scale meta-analysis on error monitoring in adults with ADHD including seven electrophysiology studies with both flanker and Go/NoGo tasks concluded that Pe-differences in flanker tasks were not robust, but that Pe amplitudes were consistently lower in individuals with ADHD in Go/NoGo tasks. ERN amplitudes were significantly reduced in adults with ADHD in both types of task. Behaviorally, higher error rates and overall slower response times (RTs) were present in the ADHD group .While research into performance monitoring commonly considers response-related EEG/ERP components, the initial stimulus processing and evaluation leading up to a response is equally relevant. The N2 and P3 are the main components in the post-stimulus interval that indicate stimulus evaluation, response selection, and sensitivity to manipulation of stimulus/response conflict. ERP studies in children with ADHD show reduced component amplitudes also during attentional processing in the P3 range . In a seThe available literature is not definitive regarding possible electrophysiological impairments in people with ADHD, and few studies have investigated the relationship between electrophysiological measures and symptom severity. We therefore tested a sample of adults with ADHD with a broad age range (19–55 years) in a speeded variant flanker task. Their behavioral performances, and stimulus and response processing were assessed by an ERP paradigm, and their results were compared to results in a control group and correlated with an ADHD symptom score.It is worth noting that intra-individual variability is generally higher in ADHD than in control populations , and thaAge is another important element of variation that will be statistically controlled for in this report, both because ADHD symptoms change across the lifespan , and becAt the outset, we hypothesized that adults with ADHD would display reduced P3, ERN, and Pe components, as well as slower RT and reduced accuracy (ACC) for participants with ADHD compared to controls. We also hypothesized that amplitude reductions relate to higher symptom load within the patient group.The participants of the present study were recruited from a larger Norwegian project on adults with ADHD. In the main study, all participants with ADHD were formally diagnosed according to national guidelines on referral from a National registry of adults in Norway and from psychologists and psychiatrists nation-wide. These guidelines were developed by an expert committee according to current criteria in the International Classification of Diseases – Tenth Revision ICD-10;  with theA sample of individuals in the same age range as the patients was recruited from the general population in Norway through the Medical Birth Registry of Norway (MBRN) to serve as control group. The project was approved by the Regional Committee for Medical and Health Research Ethics of Western Norway [Institutional Review Board (IRB) 00001872]. Further details concerning the main study are described in previous publications , 2010.n = 80 with ADHD and n = 80 controls) . The ADHD group included 31 adults (age range = 19–55 years) and the control group 32 adults (age range = 19–45 years). Ethical approval for this study was obtained from the Regional Committee for Medical Research Ethics, West-Norway, and written informed consent in accordance with the Declaration of Helsinki was obtained from all participants. Full-scale intelligence quotient (FSIQ) was assessed by two subtests (Matrix Reasoning and Vocabulary) from the Wechsler-Abbreviated Scale of Intelligence (Table 1), shown to be a useful tool to identify adult ADHD , autism spectrum disorders , bipolar disorder (ADHD N = 2), alcohol-related problems (ADHD N = 2), drug-related problems (ADHD N = 2), treatment for other mental health problems (ADHD N = 8), and eating disorders (ADHD N = 4). Participants taking stimulants (ADHD N = 14) were asked to refrain from medication 48 h prior to investigation. Other types of medication  were taken as prescribed.A subsample from the main study living in or around the Bergen municipality was invited to take part in an extended clinical examination including a set of neuropsychological tests and a psychiatric interview .Participants were instructed to fixate a dot in the center of the PC screen. The dot was present in a fixed inter-trial interval of 800 ms without jitter. Trials began with six horizontal flanking arrows below the fixation dot that were shown for 100 ms and then followed by the appearance of a center target arrow that either pointed in the same direction as the flanking arrows ( < < < < < < < or > > > > > > > ), or in the opposite direction, ( < < < > < < < or > > > < > > > ), yielding compatible and incompatible trials, respectively. Participants were asked to respond as fast and accurate as possible with a mouse button click with their preferred hand in same direction as the target arrow. Trials remained on screen until a response button press was registered. Simple feedback was given on erroneous trials “x,” or on trials with RTs extending an adaptive threshold “!,” i.e., when RTs slower than the cumulative mean RT+1.5 standard deviations. The total trial interval was therefore partially self-paced around 1500 ms, i.e., 900 ms plus the individual RTs. Each participant completed 520 trials in a randomized sequence divided into two blocks with a short break in between. Overall, probability for right/left as well as compatible/incompatible was kept as 0.5.Recordings took place in an electro-magnetically shielded chamber . A 64-channel equidistant electrode cap with Ag/AgCl electrodes  was used. Data were sampled at 1000 Hz frequency with Brain Amp amplifiers . The recording reference was placed at Cz, with a ground placed at approximately AFz. The data were offline re-referenced to the common average. Electrocardiogram was recorded from an additional channel. Impedances were kept below 10 kΩ. EEG data were pre-processed with MATLAB  with the EEGLAB toolbox  and in-hAfter visual inspection to rule out EEG abnormalities, and pervasive signal artifacts, we performed automatic artifact rejection in order to denoise the data prior to independent component analysis (ICA). EEG epochs were detrended, and we computed for each channel the root mean-squared signal, as well as its differential, the standard deviation, skewness, kurtosis of the time series, and dynamic range of the power spectrum. These measures were normalized to unit variance, and epochs falling within ±1 standard deviation were retained for further analysis, concatenated, and subjected to temporal ICA using Infomax . In ordeFigure 1).We identified N2 (340 ms) and P3 (440 ms) in the stimulus-locked grand averages and extracted averaged peaks from 40 ms long-time windows centered on the peak latency. In response-locked traces, peak extraction of the ERN was done by peak-to-peak analysis for 20–60 ms subtracted from the immediately preceding motor positivity (-40 – 0 ms), while the Pe was estimated from 180 to 220 ms post-response . To control for possible influence of age, we also included age as continuous predictor for the behavioral data, and additionally RT for the ERP components. All statistical tests were considered significant at p < 0.05. Relevant interaction effects were followed up with post hoc tests. Further, significant results were followed up by Pearson’s correlations to investigate associations between neurophysiological data and ADHD symptoms in the ADHD group. The effect-size indicator partial eta-squared  with excessive error rates >25% were excluded from the analyses, another (ADHD N = 1) due to lack of incompatible errors in the flanker task. One participant had to be excluded due to a technical error during EEG recording (ADHD N = 1). Three participants from the control sample had cutoff scores above the threshold for probable ADHD on the ASRS and were therefore also excluded. The remaining sample consisted of 55 participants, with 27 ADHD and 28 control participants, 28 males and 27 females.Statistics were computed in Matlab and Statistica . To address our main question, we estimated the compatibility effects and tested for differences between the groups. Compatibility effects refer to the difference between compatible and incompatible conditions, and were investigated for the behavioral measures RTs, ACC, and RT variability (sdRT), as well as the stimulus-locked ERPs N2 and P3 with repeated-measure analyses of variance (ANOVA) with compatibility as within-subject factor. We further investigated group differences of the error-specific response-locked ERPs ERN and Pe with correctness as within-subject factor and diagnosis as between-subject factor , and adults with ADHD showed a trend toward diverging effects of compatibility . ACC increased with age .Both groups showed a typical flanker compatibility effect with more errors in incompatible trials . While RTs did not differ between groups overall  , there was a trend toward larger RT increase under conflict in participants with ADHD when compared with controls  .Reaction time variability did not show significant effects of compatibility, age, diagnosis, or any significant interactions . . However, a trend toward more enhanced N2 amplitudes was seen with slower RTs .Amplitudes of N2 did not show differences for diagnosis, age, compatibility, or their interactions , the compatibility effect was more pronounced in the controls  .P3 amplitudes were smaller in younger than older participants . Amplitudes were larger with overall faster RTs  while amplitudes did not differ with age  .Clear ERNs were seen for erroneous responses  and erroneous (r = -0.59) trials .The mean amplitude of the Pe component estimated for error trials was much larger than for correct responses  and the response-locked ERN . Significant negative correlations were found between ASRS scores and the stimulus-locked incompatible P3  .We explored the correlation of ASRS total scores and ASRS inattentive sub-scores with behavioral measures of error rates as well as with stimulus-locked incompatible P3 and response-locked component amplitudes within the ADHD group. A significant positive correlation was found between the ASRS scores and error rates in incompatible trials , suggesting that (premature) error commission indeed starts early during stimulus processing  immediately after erroneous responses that are followed by a subsequent increased positivity (Pe). The ERN was larger for controls than for adults with ADHD. This is in line with a recent meta-analysis comparing ADHD with controls and reporting an overall attenuation of ERN in performance-monitoring tasks . The attocessing  and may After the early error detection, reflected by the ERN, the following stage of error processing, reflected by the Pe, also appeared to be hampered in adults with ADHD in our study. While the ERN was found to be present on both recognized and unrecognized errors, the Pe was present only in trials on which the subjects were aware of their errors . Based oAmong the limitations of our study, the relatively small sample size should be mentioned, which also limited the possibility to analyze the effect of comorbidities, gender, and use of medication. Ideally, the impact of comorbid conditions and medication should be assessed separately, and in more detail, however, we performed exploratory analyses between these subsamples in the dependent measures and did not find any significant differences between the subsamples. Furthermore, the ADHD patients recruited in this study were relatively well-functioning, making it difficult to transfer the results to other more impaired clinical samples .Taken together, the present examination of cognitive processes related to performance monitoring in adults with ADHD adds to our knowledge of electrophysiological correlates of monitoring and response control deficits in adults with ADHD. Adults with ADHD show attenuated P3, ERN, and Pe, which points to an impairment of attentional resource allocation in demanding conditions, automatic error detection, as well as error awareness. Behavioral performance measures were not significantly different between the groups, while group differences were more readily seen in ERP measures. This suggests that the ERP measures are even more sensitive to the underlying liability for ADHD than the overt behavioral task performance. Future work on ADHD might benefit from focusing on these early processes of performance and error monitoring to further delineate the pathogenesis of ADHD. Such results may aid in development of intervention strategies, especially targeting the increased requirements of self-management in the life of adult ADHD patients.HE, JH, AL, and TE were involved in the conception and design of the work. HE, LM, and TE were involved in the acquisition of the data. HE, LM, and TE were involved in the analysis and interpretation of data and writing of the article. HE, LM, AL, JH, and TE were involved in the critical review of article and agreement to be accountable for all aspects of the work.JH has served as a speaker for Eli-Lilly, HB Pharma, and Shire. The other 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.


The cerebellum, although traditionally considered a motor structure, has been increasingly recognized to play a role in regulating executive function, the dysfunction of which is a factor in attention-deficit/hyperactivity disorder (ADHD). Additionally, catechol-O-methyltransferase (COMT) polymorphism has been reported to be associated with executive function. We examined whether the cortico-cerebellar executive function network is altered in children with ADHD and whether COMT polymorphism is associated with the altered network. Thirty-one children with ADHD and thirty age- and IQ-matched typically developing (TD) controls underwent resting-state functional MRI, and functional connectivity of executive function-related Crus I/II in the cerebellum was analysed. COMT Val158Met genotype data were also obtained from children with ADHD. Relative to TD controls, children with ADHD showed significantly lower functional connectivity of the right Crus I/II with the left dorsolateral prefrontal cortex. Additionally, the functional connectivity of children with ADHD was modulated by COMT polymorphism, with Met-carriers exhibiting significantly lower functional connectivity than the Val/Val genotype. These results suggest the existence of variations, such as ethnic differences, in COMT genetic effects on the cortico-cerebellar executive function network. These variations contribute to heterogeneity in ADHD. Further neuroimaging genetics study might lead to the development of fundamental therapies that target ADHD pathophysiology. It was recently reported that the prevalence of ADHD is approximately 7.2%2. ADHD is more common in boys than girls 3. Children with ADHD have difficulties in daily life, and in adolescence, they often have a variety of comorbidities such as oppositional defiant disorder, conduct disorder, depression, and anxiety disorder. Additionally, ADHD often persist into adulthood, and adults with ADHD have a high risk of substance abuse disorders, suicide, and personality disorders1. Thus, ADHD is associated with distress and morbidity across the life span.Attention-deficit/hyperactivity disorder (ADHD) is one of the most commonly diagnosed neurodevelopmental disorders in childhood, characterized by symptoms of age-inappropriate inattention, hyperactivity, and impulsivity4. It is well known that the prefrontal cortex plays an important role in executive function, and that patients with ADHD often have problems in the frontal-striatal network, which includes the prefrontal cortex6.Impaired executive function is one of the most widespread findings in ADHD. Executive function comprises a set of neurocognitive processes that maintain an appropriate problem-solving set to attain a future goal, and involves response inhibition, working memory, and planning9. Previous fMRI studies have revealed decreased cerebellar activation in patients with ADHD during working memory and go/no-go tasks12. Structural neuroimaging studies have revealed reduced cerebellar volumes in patients with ADHD15. Although these neuroimaging modalities focus primarily on the properties of discrete brain regions, several previous psychopathological studies have adopted a circuit perspective, which posits that psychological disorders do not stem from anomalies in discrete brain regions16.Although the cerebellum is traditionally considered a motor structure, it has been recognized to play a role in regulating cognitive function, including executive function17.In contrast, the recent resting state fMRI (rs-fMRI) approach facilitates the evaluation of neural circuit-level brain function more easily. Further, this method is suitable for young participants, and particularly for clinical populations, such as individuals with ADHD who have behavioural and compliance issues. This is because rs-fMRI has low cognitive demands , and the scan time is relatively short compared to task-based fMRI7. The cerebellum is divided into sub-regions. Among these sub-regions, Crus I/II, is linked both functionally and anatomically with the prefrontal cortex, is involved in executive function19, and is included in the executive control network21. We focused on this network, and hypothesized that the cortico-cerebellar functional connectivity of Crus I/II with the prefrontal cortex is altered in children with ADHD.The cerebellum is reported to form neural circuits with the cerebral cortex. In fact, most of the human cerebellum is linked to cerebral association networks23. Regarding disease heterogeneity, catechol-O-methyltransferase (COMT) polymorphism has been reported to be involved with the pathogenesis of ADHD, especially with respect to executive function25. COMT is a key enzyme in the elimination of dopamine, and a single nucleotide polymorphism (SNP) Val158Met (rs4680) affects COMT activity. Those with Val158 alleles have increased COMT activity, which leads to lower dopamine levels and relatively lower prefrontal cognitive function than in individuals with Met158 alleles26. Interestingly, considerable COMT protein and mRNA have been detected in the cerebellum and in the frontal lobes27. Additionally, the cerebellum has dopaminergic innervation and dopamine receptors, similar to the prefrontal cortex28. Crus I/II in the cerebellum makes a circuit with the prefrontal cortex19 such that the stimulation of the cerebellar cortex increases dopamine efflux in the prefrontal cortex29. Furthermore, COMT genotype is reported to affect perfusion of the frontal and lateral cerebellar regions in children during rest30. We therefore considered the possibility that COMT polymorphism affects cortico-cerebellar functional connectivity of executive function via changes in dopamine levels. We also hypothesized that functional connectivity affects executive function and ADHD symptoms, and leads to heterogeneity in ADHD.Children with ADHD have variations in clinical symptoms, even within the same diagnostic category subtype. Hence, they might have uncertain etiological and neuropsychological heterogeneityThe present study aimed to determine whether cortico-cerebellar functional connectivity of Crus I/II, which is implicated in executive function, is altered in children with ADHD. Further, we examined whether COMT polymorphism is associated with altered cortico-cerebellar functional connectivity of Crus I/II in children with ADHD.p < 0.001; Table Demographic and clinical characteristics of the study participants are presented in Table p = 0.207, hyperactivity/impulsivity (T): p = 0.311, executive function (T): p = 0.657).Based on the COMT genotype, children with ADHD were divided into Val/Val (n = 15) and Met-carriers . No significant deviation from Hardy-Weinberg equilibrium was observed for the SNP in this study. There were no significant differences between Met-carriers and Val/Val groups on all demographic data including Conners scores (inattention (T): x = −38, y = 10, z = 48; cluster size = 311 voxels; p = 0.011, family wise error (FWE) corrected at cluster level). No regions were significantly associated with higher functional connectivity in children with ADHD  across all subjects, although no significant correlations were found within ADHD or TD groups .Compared to TD controls, children with ADHD showed significantly lower functional connectivity of the right Crus I/II with the left dorsolateral prefrontal cortex  coordinates: p = 0.021; Fig. Finally, we examined if COMT polymorphism was associated with the ADHD-related altered functional connectivity between the right Crus I/II and left DLPFC. The functional connectivity eigenvariates from the identified cluster were extracted and used for between-genotype comparisons. Met-carriers exhibited significantly lower functional connectivity of the right Crus I/II with the left DLPFC than the Val/Val genotype p = 0.01; Fig. 2The present study elucidated whether the cortico-cerebellar network involved with executive function is abnormal in children with ADHD, by assessing functional connectivity of the bilateral Crus I/II in the cerebellum, and whether COMT polymorphism is associated with the network. This study provides preliminary evidence of lower functional connectivity of the right Crus I/II in the cerebellum with the left DLPFC in children with ADHD versus TD controls. Further, we found that the lower functional connectivity of children with ADHD was modulated by COMT polymorphism, with Met-carriers exhibiting significantly lower functional connectivity than the Val/Val genotype. These results suggest the possibility of gene-brain interactions between the cortico-cerebellar executive function network and COMT polymorphism, which influence heterogeneity in ADHD.31. Previous fMRI studies using attention tasks in children with ADHD specifically reported functional abnormalities of the DLPFC33. Several rs-fMRI studies have reported abnormal fronto-cerebellar networks in children with ADHD36. Interestingly, Li et al.35 reported reduced functional connectivity between the left orbitofrontal cortex and left lobule VI in the cerebellum in children with ADHD. This finding is consistent with that of our study, by suggesting that connectivity of the fronto-cerebellar network is decreased in ADHD. Lobule VI in the cerebellum primarily contributes to the salience network9, which plays a crucial role in identifying the most biologically and cognitively relevant events, so as to adaptively guide attention and behaviour; the region has been suggested as being related to ADHD37. In contrast, in the present study we focused particularly on Crus I/II, which subserves executive function. A meta-analysis of voxel-based morphometric studies reported decreased volume of the right Crus I in children with ADHD13. Moreover, it has been reported that inattention and hyperactivity/impulsivity symptoms are caused by damage to the cerebellar posterior lobe, which includes Crus I/II38. Previous rs-fMRI studies reported that both Crus I/II and DLPFC are included in the executive control network21. Together, these results suggest that reduced functional connectivity of the Crus I/II with the DLPFC in children with ADHD affects executive function, which may lead to ADHD symptoms.DLPFC plays an important role in regulating executive function, including working memory and attention26. It has been also reported that COMT gene variants have particular evolutionary advantages. Specifically, Val158 alleles may be associated with an advantage in the processing of aversive stimuli, while Met158 alleles may be associated with an advantage in memory and attention tasks39. In the present study, Met-carriers had lower ADHD-related functional connectivity than Val/Val individuals had and TD controls, showing that Japanese children with ADHD exhibit the opposite pattern to that found in Caucasians. Our recent study and those of others have demonstrated that COMT may have differential effects across ethnic samples41. While Caucasians with the Met-allele have better cognitive performance than Val homozygotes43, Asians with Val homozygotes perform better in cognitive tests than those with the Met-allele45. Similarly, Met-carrier individuals with ADHD have less striatal gray matter volume than those with the Val/Val genotype in Japanese samples in contrast to Caucasians46. Thus, the present study supports the existence of an ethnic difference in the COMT genetic concomitants between Caucasians and Asians. Such ethnic differences in COMT genetic effects may be explained by the theoretical inverted-U model. This model describes an association between dopamine levels and cognitive performance dependent on the COMT Val158Met genotype. According to this inverted-U model48, optimal cognitive performance is not associated with maximal, but rather optimal dopamine levels. It can be proposed that baseline dopamine levels on the curve are influenced by an interaction between ethnicity and COMT genotype. Caucasian individuals fall on the left side of the inverted U-shaped curve. Therefore, COMT Val homozygosity is more strongly associated with poorer cognitive performance in these individuals. In contrast, Asian individuals fall on the right side of this curve. As a result, COMT Met carriers who are Asian have poorer cognitive function. High COMT protein and mRNA levels have been detected in the cerebellum and in the frontal lobes27. It is also known that stimulation of the cerebellar cortex increases dopamine efflux in the prefrontal cortex. Together, these observations suggest that COMT polymorphism may affect dopamine levels, which may then affect the cortico-cerebellar executive function network. Furthermore, COMT may have different effects on ADHD-related functional connectivity in different ethnic groups and on cognitive performance in ADHD. This gene-brain interaction between the cortico-cerebellar executive function network and COMT polymorphism may be associated with heterogeneity in ADHD. However, although we have discussed this finding in terms of a potential cause and effect mechanism, it must be emphasized that our evidence only supports an association.Curiously, we found that COMT polymorphism was associated with functional connectivity of the right Crus I/II with the left DLPFC in children with ADHD, and the functional connectivity in Met-carriers was significantly lower than in Val/Val individuals. Generally, those with Val158 alleles have increased COMT activity, leading to lower dopamine levels, which in turn leads to deficits in prefrontal cognitive function when compared to individuals with Met158 alleles22. Regarding capturing the underlying pathophysiological mechanisms, brain-imaging genetics studies, which primarily identify genes that influence variation among brains, are increasingly prevalent. In vivo neuroimaging studies that elucidate endophenotypes of neurodevelopmental disorders combined with genetic actions will help to identify the risk genes, and investigations of these brain function related genes will help validate their association with disease49. Although some imaging genetics studies of ADHD have been reported51, the present study is the first to examine the influence of COMT polymorphism on resting-state functional connectivity in patients with ADHD. Neurodevelopmental disorders such as ADHD are addressed as disorders of brain circuitry22. Recently, nodal centrality measures  have been used to quantify brain network connectivity. Imaging genetics studies using these analyses would help to clarify the underlying neuronal mechanisms and provide a new framework for classification based on such mechanisms. This could lead to the development of fundamental treatment strategies that consider the underlying pathophysiology.Although the DSM criteria are categorical, being primarily based on the signs and symptoms present, in fact categorical diagnosis remains uncertain with respect to disease heterogeneity. Thus, studies that adopt this categorical classification are limited, in that a categorical diagnosis does not necessarily capture currently unknown mechanisms of dysfunction. The National Institute of Mental Health in the United States launched the Research Domain Criteria (RDoC) project to create a framework for research on pathophysiology, especially for genomics and neuroscience. They expect that identifying syndromes on the basis of pathophysiology will eventually improve outcomes for psychiatric diseases, as well as cancer, heart disease, and infectious diseases52. Second, gene-gene interactions were not considered. The COMT genetic effects may be influenced by other common variations in dopamine-regulating genes, such as monoamine oxidase41. We also did not examine the genotypes of TD controls, and the effects of COMT polymorphism in TD controls. In the present study, we focused on heterogeneity of ADHD as it related to COMT polymorphism. Third, dysfunction of the DLPFC has been also described in developmental coordination disorder (DCD)53, which is frequently comorbid with ADHD. We evaluated 11 of 31 patients with ADHD in the present study using a standard assessment tool for DCD, the Movement Assessment Battery for Children Second Edition (M-ABC2), which was recently reported in another study54. Although 10 patients had no difficulty with movement, one was at risk of having movement difficulties. Additionally, we did not evaluate the remaining patients with ADHD using the M-ABC2. Hence, some patients with ADHD in the present study may also have had DCD, which may have affected the results. Finally, participants were of a wide range of ages and the sample size of the patient group was relatively small. We must consider that the brain changes dynamically with age55, although we matched ages between groups and included age as a covariate to minimize its effect on the results. Our observations have been made in small samples and are thus speculative and need to be replicated in larger samples. Further, although rs-fMRI studies are increasingly used to understand the effects of disease processes on neuronal networks, caution is required when interpreting functional connectivity changes in cortico-cerebellar networks.This study is subject to several limitations. First, the children with ADHD included patients of combined type or predominantly inattentive type, and patients who were not drug naïve. Medication status might affect functional connectivityIn conclusion, this study showed that children with ADHD had significantly lower functional connectivity between the right Crus I/II and the left DLPFC compared to TD controls, and COMT polymorphism was associated with functional connectivity in children with ADHD. These results suggest that gene-brain interactions between cortico-cerebellar executive function networks and COMT polymorphism influence heterogeneity in ADHD. Further imaging genetics studies using rs-fMRI might clarify the underlying pathophysiological mechanisms, which might lead to the development of fundamental therapies that accord with pathophysiology.The protocol was approved by the Ethics Committee of the University of Fukui (Assurance no. 20110104) and was conducted in accordance with the Declaration of Helsinki and the Ethical Guidelines for Clinical Studies of the Ministry of Health, Labour and Welfare of Japan. After a complete explanation of the study, all participants and the parent(s) provided written informed consent and assent for participation in this study. This study is registered with the University Hospital Medical Information Network (UMIN000025830).1, and comorbid diseases were evaluated by semi-structured diagnostic interview, via the Mini International Neuropsychiatric Interview for Children and Adolescents - Japanese version (MINI-KID)56.In total, 33 boys with ADHD, who were referred to our laboratory, were recruited for the present study at the University of Fukui Hospital, Japan. The diagnosis of ADHD was based on the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5)Age-matched controls consisted of 30 TD school boys aged 7–14 years, who were recruited from the community. We confirmed the presence of no psychiatric diseases in TD controls by MINI-KID. This group had no family history of psychiatric diseases.57. Parents of each group were asked to complete Conners 3 instrument58 to evaluate executive function, inattention, and hyperactivity/impulsivity symptoms. The Hollingshead Index of Social Position was administered as a composite measure of SES59, and handedness was assessed according to the Edinburgh Handedness Inventory60.Intellectual capacities were estimated via the Wechsler Intelligence Scale for Children-Fourth (WISC-IV)61.Exclusion criteria for both groups were any contraindications for MRI, FSIQ < 70, any history of other neurodevelopmental disorders , severe head trauma, neurological abnormalities , psychiatric diseases except for oppositional defiant disorder and conduct disorder, any history of child maltreatment, and excessive head motion  during the scanning. All participants were medication-free prior to MRI for at least 5 times half-lives, including methylphenidate and atomoxetine, consistent with previous studiesGenomic DNA was extracted from the peripheral blood via the standard phenol-chloroform method using the QIAamp DNA Micro Kit  in accordance with the manufacturer’s instructions. Two children with ADHD underwent extraction from oral mucosa because they rejected blood sampling. COMT Val158Met polymorphism (rs4680) was genotyped by real-time polymerase chain reaction (RT-PCR) analysis using the StepOnePlus System  in accordance with standard protocols provided by the manufacturer.17.Functional images were acquired with a T2*-weighted gradient-echo echo-planar imaging (EPI) sequence via a 3-T scanner  and a 32-channnel head coil. In total, 201 volumes were acquired for a total scanning time of 7 minutes 42 seconds. Each volume consisted of 40 slices, with a thickness of 3.5 mm and a 0.5-mm gap to cover the entire brain. The time interval between each successive acquisition of the same slice  was 2300 ms, with an echo time (TE) of 30 ms, and a flip angle (FA) of 81°. The field of view (FOV) was 192 × 192 mm, and the matrix size was 64 × 64, yielding volume dimensions of 3 × 3 mm. The participants were instructed to stay awake but close their eyes and think of nothing in particular. Participant movement was further minimized by the placement of memory-foam pillows around their headhttp://www.fil.ion.ucl.ac.uk/spm/), a data processing assistant, and resting-state fMRI software (DPARSF)62 with the following steps. First, the initial 10 volumes were discarded, and slice-timing correction was not applied, followed by spatial realignment of 191 volumes to the mean volume. The signal from each slice was realigned temporally to that obtained from the middle slice using sinc interpolation. To control for motion confounds in our data, we investigated the effects of head motion by computing the mean frame-to-frame RMS motion63, and FD64 obtained during the realignment process. The re-sliced volumes were normalized to MNI space with a voxel size of 2 × 2 × 2 mm3 using the EPI template provided by SPM12. The normalized images were spatially smoothed with a 6-mm Gaussian kernel. Next, the linear trend in the time series was removed, and temporal bandpass filtering (0.01–0.08 Hz) was performed to reduce the effects of low-frequency drift and high-frequency noise. The non-neural noise in the time series was controlled, and several sources of spurious variance  were eliminated from the data through linear regression17. We also performed a similar analysis after we removed frames with FD > 0.5 mm (scrubbing) during preprocessing65. We describe the results in the supplementary information section  for the whole brain, and individual’s r-values were then normalized to z-values using Fisher’s z-transformation. For group comparisons, we examined differences via a two-sample t-test (ADHD versus TD), including age and FSIQ as covariates in the model due to their potential confounding effects34. The statistical threshold was set at p < 0.05 with FWE correction for multiple comparisons at the cluster level (height threshold of p < 0.001). Further, the relationship between ADHD-related functional connectivity of Crus I/II and Conners executive function scores was investigated using Pearson’s correlation coefficients.We analysed seed-based functional connectivity using a seed region  correlation approach. Bilateral Crus I/II in the cerebellum was selected as the seed region because Crus I/II is particularly involved with executive functiont-tests. Eigenvariates were extracted from the identified cluster. The eigenvariate is a measure of the central tendency of the cluster, which is robust to the heterogeneity of the response within the cluster. The functional connectivity eigenvariates indicate the degree of functional connectivity of Crus I/II with the cluster69.To further determine whether COMT polymorphism was associated with ADHD-related functional connectivity alterations of Crus I/II, the ADHD-related functional connectivity of Crus I/II was compared between the two COMT groups , using Welch’s t-test for numerical variables and chi-square tests for categorical valuables. All statistical tests  were two-tailed; p-values less than 0.05 were considered statistically significant. Statistical analyses were performed using the Statistical Package for the Social Sciences 23 software .Demographic data are expressed as the mean ± SD. The clinical values were compared between groups using Welch’s Supplementary information


Cohort studies often report findings on children with Attention Deficit Hyperactivity Disorder (ADHD) but may be biased by self-selection. The representativeness of cohort studies needs to be investigated to determine whether their findings can be generalised to the general child population. The aim of the present study was to examine the representativeness of child ADHD in the Norwegian Mother and Child Cohort Study (MoBa).The study population was children born between January 1, 2000 and December 31, 2008 registered with hyperkinetic disorders (hereafter ADHD) in the Norwegian Patient Registry during the years 2008–2013, and two groups of children with ADHD were identified in: 1. MoBa and 2. The general child population. We used the multiaxial International Classification of Diseases (ICD-10) and compared the proportions of comorbid disorders (axes I–III), abnormal psychosocial situations (axis V) and child global functioning (axis VI) between these two groups. We also compared the relative differences in the multiaxial classifications for boys and girls and for children with/without axis I comorbidity, respectively in these two groups of children with ADHD.p < 0.0001. The proportions of comorbid axis I, II, and III disorders were low, with no significant group differences. Compared with the general child population with ADHD, children with ADHD in MoBa were registered with fewer abnormal psychosocial situations  and better child global functioning . When analysing relative differences in the two groups, essentially the same patterns were found for boys and girls and for children with/without axis I comorbidity.A total of 11 119 children were registered with ADHD, with significantly fewer in MoBa (1.45%) than the general child population (2.11%), Self-selection was found to affect the proportions of ADHD, psychosocial adversity and child global functioning in the cohort. However, the differences from the general population were small. This indicates that studies on ADHD and multiaxial classifications in MoBa, as well as other cohort studies with similar self-selection biases, may have reasonable generalisability to the general child population. Attention Deficit Hyperactivity Disorder (ADHD) is a heritable, neurodevelopmental disorder with childhood onset, characterized by persistence of hyperactivity, impulsivity and attention deficit , 2. The n = 1478), similar rates of psychiatric disorders were found in boys and girls when assessed by clinicians, although parents described more emotional symptoms in girls [In children with ADHD, comorbid disorders are more common than not; prevalence rates of 67% and 69% were reported in two large clinical European and American multisite studies . Comorbiin girls . The genPopulation studies are designed to detect genetic- and environmental causes of disease, and frequently present findings about ADHD –26. HoweThe Norwegian Mother and Child Cohort Study (MoBa), involving about 110 000 children followed from pregnancy onwards, represents a unique opportunity to investigate risk factors, developmental trajectories and clinical features of mental disorders such as ADHD . HoweverThe present study reports on data from a nationwide patient registry using the Multiaxial Classification of Child and Adolescent Psychiatric Disorders , 40 on cTo our knowledge, the present study is the first to use information from all axes on the Multiaxial Classification of Child and Adolescent Psychiatric Disorders  in childa. Compare the proportions of ADHD in MoBa and the general child population,b. Compare the proportions of comorbid disorders, abnormal psychosocial situations and child global functioning in these two ADHD groups.Investigate the relative differences in multiaxial classifications for boys and girls and for children with/without axis I comorbidity, respectively, in these two ADHD groups.The aim of the present study was to examine the representativeness of child ADHD in the MoBa by using these multiaxial classifications, as reported to the Norwegian Patient Registry from CAMHS, to:There would be a lower proportion of ADHD in MoBa than in the general child population, as well as better psychosocial- and global functioning for children with ADHD in MoBa; andThere would be few relative differences in multiaxial classifications for boys and girls, and for children with/without axis I comorbidity in the two ADHD groups.Based on previous research, we hypothesized thatThe present study included all Norwegian children born between January 1, 2000 and December 31, 2008 that were registered with a diagnosis of ADHD reported by CAMHS to the National Patient Registry (NPR) between January 1, 2008 and December 31, 2013. In Norway, health services use the International Classification of Diseases, 10th ed. , with thhttps://www.fhi.no/studier/moba/) is a prospective population-based cohort study conducted by the Norwegian Institute of Public Health [There were 524 726 children born in Norway in the defined time period (269 733 boys and 255 993 girls) , 110 230c Health , 44. Of c Health , 35, 44.The Norwegian Patient Registry (NPR) is a national health-care registry that receives patient-data reported from all the specialized mental health care services in Norway, including the CAMHS. According to the Norwegian Health Register Act and the NPR-regulation passed by the Norwegian parliament in 2007 it is mandatory for the specialized health-care services to report health-care data to the NPR. Consequently, individual-level health data are available from 2008 onward. The personal identification numbers are stored in encrypted form in the NPR. NPR receives diagnoses from CAMHS in accordance with the Multiaxial Classification of Child and Adolescent Psychiatric Disorders , which iFor the present study, identification of the MoBa participants in the NPR was submitted to the co-author employed at the NPR, through the personal identification number. The same co-author extracted descriptive NPR data (see below) and the multiaxial classification data for children with ADHD in MoBa and in the general population. The NPR provided anonymous information from the registry to the current group of authors.This information includes descriptive data in the form of gender, age at first CAMHS-contact and at first ADHD diagnosis, number of days and contacts in CAMHS and the multiaxial classification data: Comorbid child psychiatric disorders (axis I), learning- and intellectual disabilities (axes II and III), epilepsy (axis IV), the associated abnormal psychosocial situations (axis V), see Table t-test (mean) or one sample Wilcoxon (median) for continuous variables, as appropriate, thereby accounting for the inter-dependency between children with ADHD in the MoBa and in the general child population.The characteristics of the two groups of children registered with ADHD in MoBa and the general population are given as number of participants, proportions (%), means, and Cohen’s d, as appropriate. The gender distributions were estimated as odds ratios. The two ADHD groups were compared by using one sample binomial test for categorical variables, and one sample t-test, and Cohen’s d expressed the magnitude and direction of differences. .We also compared the relative differences in the multiaxial classifications for boys and girls and for children with/without axis I comorbidity, respectively in these two groups of children with ADHD. For categorical variables, we used the ratio of relative frequencies where ratios below 1 indicated under-representation of the characteristic in MoBa, whereas a ratio above 1 indicated over-representation. For continuous variables, we used a one-sample p < 0.0001).Among the 524 726 Norwegian children born between January 1, 2000 and December 31, 2008, a total of 11 119 children (2.11%) were registered in the NPR with an ADHD diagnosis between January 1, 2008 and December 31, 2013, significantly more than among children in the MoBa, where 1.45% (1595/110 230) were registered with ADHD (p < 0.001) in the general child population, and in the MoBa .Boys had higher odds ratio (OR) for having ADHD than girls .The MoBa participants were approximately 0.6 years younger at first contact with CAMHS, and 0.5 years younger when first registered with an ADHD diagnosis compared with the general child population  or epilepsy (axis IV). Abnormal psychosocial situations registered on axis V were significantly less frequent in children with ADHD in MoBa compared to children with ADHD in the general child population, and child global functioning was significantly better in MoBa, with effect sizes < .30  found in the present study (30%) was lower than the 52%  and 76.7n = 14 825), which reported a mean CGAS of 55 [As hypothesized, we found fewer abnormal psychosocial situations (axis V) in children with ADHD in MoBa than in the general child population. This is in accordance with studies reporting that the frequency of clinical ADHD is elevated in socio-economically disadvantaged groups , 56 withAS of 55 . HoweverThat children with ADHD in MoBa were significantly younger at first contact with CAMHS (and when first registered with ADHD) could be related to their better-educated parents seeking help at an early age . We consEarlier studies on the representativeness of cohort studies quantified bias by also comparing relative ratios (within group associations) using registry data available for both the cohorts and the general child populations , 46. As A strength of the present study is the use of the a national patient registry which as far as all data are reported as obliged, includes all patients treated within CAMHS in Norway and provides valuable information about ADHD in CAMHS and may be considered representative of clinical practice.Our study had several limitations. First, we only included data reported to the NPR as registered by clinicians in CAMHS, thus not children diagnosed only within primary care. Second, low rates of comorbid disorders in children with ADHD may have resulted in underestimated group differences. Third, we had a follow-up period of six years and only children up until age 13 years were included. Finally, we do not know the reliability and validity of the clinically registered diagnoses.Self-selection was found to affect the proportions of ADHD, psychosocial adversity and child global functioning in the cohort. However, the differences from the general population were small. This supports that studies on ADHD and multiaxial classifications in MoBa, as well as in other cohort studies with similar self-selection biases, may have reasonable generalisability to the general child population.


The combined parent and child reports of symptoms of Oppositional Defiant Disorder from the DISC were inversely related to age (p ≤ 0.05). Understanding SS in ADHD adolescents as they move through puberty will aid clinicians in monitoring ADHD adolescents and their trajectory into high-risk behaviors.This study was designed to examine the relationship of pubertal changes and sensation seeking (SS) in adolescents with Attention Deficit Hyperactivity Disorder (ADHD). Patients with current or past histories of uncomplicated stimulant medication use for ADHD between the ages of 11 and 15 (13 ± 1.5) were recruited from a Child Psychiatry and a General Pediatric Clinic. SS was measured using the SS Scale for Children. Pubertal development was measured using Tanner staging, free testosterone, and DHEAS. Subjects and their parent were interviewed with the Diagnostic Interview Schedule for Children (DISC). SS total score was correlated with Tanner stage, free testosterone, and DHEAS (