In the last half century, the life expectancy of beta-thalassemia patients has strikingly increased mostly due to regular blood transfusions and chelation treatments. The improved survival, however, has allowed for the emergence of comorbidities, such as hearing loss, with a non-negligible impact on the patients’ quality of life. This thorough review analyzes the acquired knowledge regarding hearing impairment in this hereditary hemoglobinopathy, aiming at defining its prevalence, features, course, and possible disease- or treatment-related pathogenic factors. Following PRISMA criteria, we retrieved 60 studies published between 1979 and 2021. Diagnostic tools and criteria, forms of hearing impairment, correlations with beta-thalassemia phenotypes, age and sex, chelation treatment and laboratory findings including iron overload, were carefully searched, analyzed and summarized. In spite of the relatively high number of studies in the last 40 years, our knowledge is rather limited, and large prospective studies with homogeneous diagnostic tools and criteria are required to define all the aforementioned issues. According to the literature, the overall prevalence rate of hearing impairment is 32.3%; age, sex, and laboratory findings do not seem to correlate with hearing deficits, while the weak relationship with clinical phenotype and chelation treatment seems to highlight the presence of further yet to be identified pathogenic factors. Beta-thalassemia is a common inherited congenital disorder of hemoglobin production, resulting in hemolytic anemia and multiorgan involvement . Each yeIn the past centuries, the most severe forms led to early death due to severe anemia. Regular red cell transfusions 60 years ago changed transfusion-dependent β-thalassemia (TDT) from a fatal childhood disorder into a chronic illness . HoweverIndeed, the first chelator (deferoxamine) provided evidence of dose-related ototoxicity causing sensorineural hearing loss  that ledDespite its high prevalence and the several studies available in the literature, the true scenario of hearing loss among beta thalassemia remains rather nebulous. Most studies do not consider incorporating a healthy control group, so that relative prevalence rates are not adjusted with the regional expected prevalence. Besides, findings are strikingly heterogeneous and conflicting with prevalence rates ranging from no hearing problems at all to a hearing deficit in most patients. Discordances also encompass the type of hearing deficit, its severity, and course, with (1) conductive and mixed forms often being neglected, excluded, or not differentiated; (2) variable inclusion criteria from simple high frequency sensorineural dip to severe hypoacusia; (3) scarce information regarding the evolution. In addition, correlation with beta-thalassemia phenotype, chelation treatment, laboratory findings, age, and sex, are poorly defined and the proper management of hearing function varies from yearly investigations to no investigation at all without agreed guidelines about the preferable diagnostic tool.This comprehensive review aims to make a point about the incidence, etiology, and evolution of this disease- or treatment-related complication highlighting the issues that need further investigations.www.google.com (accessed on 31 August 2021) were screened up to August 2021, using the following keywords and meshes: “beta-thalassemia” and “hearing” or ‘acoustic‘ or ‘auditory’. All retrieved publications were evaluated, individuating the relevant ones. Duplications of pre-existing data were excluded; only articles in English, German, Spanish, Italian, or French language were included. The reference lists of the selected articles were also screened to identify additional studies. The articles were subdivided among all authors, analyzed, and summarized, excluding non-pertinent papers; all data were thereafter discussed collegially. Appropriate descriptive statistics were applied, when possible, on parametric and non-parametric variables.Following PRISMA guidelines for systematic reviews, the PubMed database, Google Scholar, and Eighty-five articles were found: 24 were excluded as the full text was not available online nor in the main Italian medical libraries; one was excluded due to Chinese language. Sixty studies were therefore considered; they included 10 case reports and two reviews. The publication years ranged from 1979 to 2021. Seven studies on mixed patients  were not considered for our review on the prevalence of hearing loss, as disaggregate data on beta-thalassemia were not retrievable. In the following paragraphs, we present and discuss in detail the literature findings.In the literature regarding beta-thalassemia, the detection of hearing impairment has been pursued with different, sometimes combined, methods, with likely implications in terms of the observed prevalence rates. Before entering the issue of results, a short overview about diagnostic tools and criteria is necessary.Clinical interviews widely underestimate hearing loss, as only a minority of beta-thalassemia patients with proven hearing abnormalities complain of hearing impairment ,13,14,15The gold standard to detecting hearing loss in clinical practice is the pure-tone audiometry (PTA). This tool can detect and categorize the degree of hearing loss according to the hearing threshold , its type , and the audiometric pattern ; PTA is even able to detect hearing deficits on a single, generally acute, tone .Even though sensorineural dip does not have a clinical impact, its presence  might represent a warning light of an ongoing pathological process, thus prompting for an audiological follow up to evaluate any progression over time of hearing damage or assess its span on contiguous frequencies. PTA relies on patients’ responses to stimuli and requires cooperative children and adults. Therefore, pure-tone audiometry represents a valid and reliable option for monitoring auditory function in all patients over the age of six. Below this age, and in children who are partially cooperative, the test can be performed in the age-adapted version of behavioral pure-tone audiometry that is feasible though less informative than the pure-tone audiometry.Otoacoustic emissions, both transiently evoked (TEOAEs) or distortion product (DPOAEs) otoacoustic emissions, are an accurate method for assessing cochlear function, especially the outer hair cell function, and they present several advantages as they are a non-invasive, objective, rapid, easy to use, and sensitive tool. They can be applied even in non-cooperative subjects and seem to be useful for the objective early detection of subclinical hearing loss, even before PTA abnormalities. However, the information given by audiometry is more comprehensive. In fact, DPOAEs are tested at specific intensities , thus not providing the whole picture of the hearing loss severity. DPOAEs’ absence might be an early sign of hearing loss, but they can also be not detectable for a natural decline of cochlear function. For this reason, DPOAEs should be considered a screening test in non-collaborative patients  and their findings should always be confirmed with other diagnostic tools . Auditory evoked potentials are also objective and can be more informative than otoacoustic emissions, as they could potentially provide a hearing threshold. However, in clinical practice, their use is limited to specific frequencies (2000–4000 Hz) to keep the length of the examination feasible to patients’ compliance. Its use is mostly limited to infants, to non-collaborative patients, or in a research setting.According to the current guidelines, the diagnosis of hearing loss is based on an average hearing threshold increase above 25 dB at 500, 1000, and 2000 Hz . However, ototoxicity primarily affects high frequency domains  and its early detection is improved by considering the decreased performance on single or contiguous high frequencies tested by PTA in one or both ears. For this reason, studies have variably considered hearing impairment above 10 , 15 17]17], 20 ,27,28, 2Beta-thalassemia has a wide phenotypic spectrum that is classically dichotomized into transfusion-dependent (TDT) and non-transfusion-dependent (NTDT) patients according to hemoglobin levels. This terminology has substituted the previous classification into beta-thalassemia major and intermedia, and the terms are almost interchangeable. However, the two classifications present some minor discrepancies as some studies considered in the “thalassemia intermedia” subgroup also included patients under regular transfusion regimen . Regarding the hearing loss issue, most studies focused on TDT patients , two of which reported disaggregate data on mixed phenotypes (27 TDT vs. 7 NTDT patients and 51 TDT vs. 20 NTDT) ,32 and tp = 0.02), though the difference was not significant considering only sensorineural hearing deficit .The mean rate of hearing loss was 29.9 ± 20% among TDT and 31.4 ± 27.9% among NTDT, but across studies both the diagnostic criteria  and the diagnostic tools for hearing loss ascertainment were highly heterogeneous, making the comparison highly arduous. In the three sole studies that included both phenotypes ,32, hearA recent large review on 1422 Iranian TDT patients  found a Most studies focused on sensorineural hearing loss (SNHL), in some cases excluding patients with conductive, mixed, or unilateral SNHL cases, as they were not attributable to chelation therapy-related ototoxicity. On the other hand, some studies included all types of hearing loss without distinguishing among subtypes of hearing loss and without specifying their prevalence rates. The latter studies were excluded from sub-analyses.SNHL prevalence rate was investigated and reported in 25 studies , while conductive hearing loss (CHL) was reported in 15 studies  and 12 studies reported the mixed form of hearing loss . However, the data are often difficult to be compared as the criteria for hearing deficit varied vastly among studies. In addition, in some studies SNHL showed improvement with chelation therapy adjustment  and in other studies CHL was transient or reversible with appropriate treatment. For example, in the study by Albera et al., 22/23 TDT patients with CHL did not present hearing deficits at follow up . The revHearing impairment is commonly associated with aging in the general population, so that a higher prevalence could be expected in adulthood in beta-thalassemia as well. However, other factors such as the disease itself or concomitant therapies and comorbidities might play a pathogenic role in beta-thalassemia, with a possible increased vulnerability in the pediatric age, as well.Most studies on hearing function in thalassemia were conducted on a mixed population, from pediatric to adult age, and results are presented as a whole group, thus not allowing comparisons between the hearing deficit in children and in adults. Among the 40 studies reporting data on prevalence of HL, 25 described a mixed group (adults and children); to note, these studies recruited young patients, with the mean ages ranging from 9  to 28 yeThree studies enrolled exclusively adults  and five only pediatric subjects ; among the latter, Alzaree et al. did not report data on patients, but on ears . p = 0.29).The hearing loss prevalence rate was slightly higher in adults  than among children  though the difference was not significant ; in contrast, no difference was found in CHL prevalence  consistently with a higher rate of middle ear disease among children; mixed HL was noted only in 6/60 adults, not reported in the pediatric studies.A comparison between adults and children was done with regards to the different hearing loss phenotypes among the TDT patients; an increased prevalence of SNHL was found in adults  and described a direct correlation with the chelation dosage but also an inverse one with ferritin levels . AccordiThe available literature however is not in agreement with regards to iron chelation’s role in causing hearing loss; our analysis shows that a correlation with the dose of the iron chelators is reported mostly when doses are higher than the recommended . Most studies were conducted on patients receiving DFO, so that data are scarce for the other two iron chelators; only in two studies deferasirox was the sole chelator used, and no study was found on patients on deferiprone monotherapy; six studies included patients on different iron chelation drugs, but they did not report separate data for each chelator . In addiLastly, no study compared the rate of hearing loss among the three different chelators or analyzed the prevalence rate among patients naive for iron chelation. Interestingly, abnormal BAEPs were registered in a group of NTDT subjects, not on iron chelation ,50, and Further investigations are therefore warranted also in not-chelated and not-transfused beta thalassemia patients to achieve more information about the role of chelation treatment in the SNHL onset. One of the main complications in TDT patients is the secondary hemochromatosis due to tissue iron deposition occurring during the disease course and the prolonged transfusion regimen. Current guidelines recommend that therapy must be started after serum ferritin levels are above 1000 μg/L. The long-term control of serum ferritin has been linked to protection from heart disease and to improved survival if levels are consistently less than 2500 μg/L , with evSerum ferritin levels have been also implicated with hearing impairment development, but the relationship is still controversial. Most authors found no significant ferritin level differences between patients with and without hearing loss ,48,58,62In the study by Porter et al. in 1989, low serum ferritin appeared as a risk factor for SNHL, since all patients with hearing impairment had serum ferritin below 2000 μg/L . This asThus, according to the available literature, both iron overload and excessive iron-chelating therapy should be prevented, and a tailored chelation treatment should be adopted.The possible relationship between hearing impairment and the severity of anemia (hemoglobin levels or number of transfusions) was investigated in eight papers. More than 1200 patients undergoing regular transfusion regimen were analyzed with the following results: abnormal PTA results and hearing loss were non-related with pre-transfusion hemoglobin ,44, duraIn a small sample of TDT patients, a hearing threshold decrease correlated with hemoglobin levels, transfusions per year, and duration since the last transfusion. These results were explained by a lower formation of insoluble alpha chains tetramers when hemoglobin increases, but no other study supported this hypothesis. Furthermore, as total transfusion numbers increased, hearing thresholds at PTA and high frequency audiometry decreased .Several studies have investigated the relationship between sex and hearing loss in order to identify additional risk factors for ototoxicity. In nine articles , the correlation between sex and hearing impairment was analyzed: most of these studies failed to detect a significant correlation ,26,27,28Tinnitus is one of the most common hearing disorders, with wide-ranging risk factors including age, hearing loss, noise exposure, inflammatory diseases, psychosocial distress, and ototoxic drugs. The latter may induce both reversible and irreversible damage of the inner ear structures causing tinnitus, with or without hearing loss and balance problems . These oData on tinnitus in thalassemic patients are rather scanty and often dispersed in the results sections. They were acquired only by means of an anamnestic interview; no study applied specific instrumental examinations or standardized questionnaires. For these reasons tinnitus is often poorly characterized in terms of its severity, disability, correlation with age, or association with hearing loss. In addition, no study included a healthy control group or mentioned the prevalence of tinnitus in the general population. In beta-thalassemia, tinnitus prevalence rate ranged widely from 3.3% to 38% ,57,62,65As tinnitus is often underreported by patients and it is frequently associated with ototoxicity, even in the absence of hearing loss, dedicated investigations by means of standardized questionnaires or acufenometry  are warranted to improve the follow up of beta-thalassemic patients.Audiological testing has become routinary practice in beta-thalassemia for multiple reasons, at least in the transfusion-dependent form. First, the need for potentially ototoxic long-lasting therapies and the ageing due to an improved life expectancy are expected to determine an increasing prevalence of hearing loss in beta-thalassemia patients. Second, hearing loss might be a precious warning light of toxicity of the ongoing therapy, thus allowing for prompt dosage adjustment; this approach was proven to often revert or reduce the perceived hearing loss ,57. ThirFew longitudinal studies are available (see “hearing loss course” section). Currently, guidelines on audiological assessment and management are missing. As during the clinical trials of iron chelation, audiological assessment was done yearly, this approach has been automatically translated in the clinical practice, even though there is no supporting evidence. Notably, even audiological data obtained during trials have been not or very scarcely published so that the reason for such a strict follow up remains obscure . Since the outset of the hearing loss is still unpredictable, audiological testing is suggested before the start of treatment to assess the hearing threshold. Audiological evaluation should be considered mandatory in the case of the onset of hearing disorders . Integrating previous suggestions , in the Despite the large number of studies addressing the topic of hearing loss in beta-thalassemia, the discrepancies in recruitment and diagnostic criteria do not allow the obtainment of a reliable and precise picture of this problem. Future longitudinal studies with a detailed description of sample, treatment, and hearing deficit will help understand the pathogenesis, the prevalence, and the best management of hearing impairment in beta-thalassemia.


Ryugu is a carbonaceous rubble-pile asteroid visited by the Hayabusa2 spacecraft. Small rubble pile asteroids record the thermal evolution of their much larger parent bodies. However, recent space weathering and/or solar heating create ambiguities between the uppermost layer observable by remote-sensing and the pristine material from the parent body. Hayabusa2 remote-sensing observations find that on the asteroid (162173) Ryugu both north and south pole regions preserve the material least processed by space weathering, which is spectrally blue carbonaceous chondritic material with a 0–3% deep 0.7-µm band absorption, indicative of Fe-bearing phyllosilicates. Here we report that spectrally blue Ryugu’s parent body experienced intensive aqueous alteration and subsequent thermal metamorphism at 570–670 K (300–400 °C), suggesting that Ryugu’s parent body was heated by radioactive decay of short-lived radionuclides possibly because of its early formation 2–2.5 Ma. The samples being brought to Earth by Hayabusa2 will give us our first insights into this epoch in solar system history. Both poles of asteroid Ryugu, the target of space mission Hayabusa2, preserve the least processed material by space weathering. Here, the authors show detection of 700 nm absorption band in the polar spectra of Ryugu, that allows to constrain the hydrothermal history of its spectrally blue parent body. Thus, carbonaceous protoplanets have probably undergone rock-ice differentiation and/or varying degrees of internal aqueous alteration2. The rubble-pile asteroid Ryugu, target of the Hayabusa2 mission, resulted from catastrophic disruptions of larger parent bodies5. Ryugu could be an ideal body to study the thermal history and water/rock ratio of pre-disruption parent bodies, much larger (~100 km) than Ryugu. Our objective is to find the most pristine material on Ryugu and to study evidence for proposed thermal metamorphism of its original parent body and consequent processes after its catastrophic disruption and re-accumulation. Stratigraphic analyses have suggested that the possible surviving, unprocessed materials are bluer than the average Ryugu reflectance spectrum6. Slightly bluer materials than the average were found on the equatorial ridge, which might be uncovered by regolith migration from the ridge to the middle latitudinal regions7. Moreover, the global observations obtained by the Hayabusa2 spacecraft discovered that the bluest materials are distributed at the polar regions of Ryugu, where both solar heating and space weathering are weakest5  Ceres and (4) Vesta. Geomorphological and spectral analyses have recently suggested the presence of liquids in the subsurface of Ceres Ceres anIn this study, we reveal the hydrated state of the main components of Ryugu, which are inherited from its parent body, based on remote-sensing observations. Here, we show the least processed materials by space weathering in Ryugu’s polar regions, which are spectrally blue and associated with 0.7-µm band absorption. This finding suggests intensive aqueous alteration and subsequent heating up to 670 K (400 °C) of Ryugu’s parent body.12. Figure 2+–Fe3+ charge transfer of oxidized iron13 and is often used as a proxy for phyllosilicates such as serpentine and saponite. Local variations in spectral slope and 0.7-µm band absorption were observed. Spectrally blue  material is concentrated on both poles, as clearly shown  and one rough facet (C) .The Telescopic Optical Navigation Camera (ONC-T) is a multi-band imager that is equipped with seven band filters ranging wavelength from 0.40 to 0.95 µm6 observations display a 2.72-µm band absorption in the spectrum of the north pole plains that shows a slightly deeper absorption than the standard reference spectrum 18. Even though the absolute value of the 0.7-µm band depth has formal uncertainties ranging from 0 to 3%, the strong correlation with the high latitude regions suggests the presence of the 0.7-µm band absorption is real. Given that the blue materials show slightly deeper 0.7-µm band absorptions on the polar regions where they are less irradiated by the Sun, we anticipate that heating or space weathering decreases the absorption features.It is known that the 0.7-µm and 2.7-µm features can be easily deformed by either heating or space weathering19. Thus, in this study, we define space weathering effects as either by solar wind irradiation or micrometeoroid bombardment. Although in the current orbit the surface temperature cannot reach 570 K, where decomposition of phyllosilicates20 can occur, Ryugu once orbited closer to the Sun7. For example, at the heliocentric distance of 0.4 au, the maximum temperature of a large part of the surface could reach >570 K and the north polar region was kept <570 K 26, negative to positive spectral slope, by space weathering. Previous experimental studies of hydrated CI and CM carbonaceous chondrites suggested that the color variation by space weathering is sensitive to not only the starting composition but also the sample characteristics (slab vs. pellet vs. loose powder) and radiation beam properties (fluence and energy)28. So far, ion irradiation experiments on hydrated carbonaceous chondrites, which simulate space weathering by solar wind, have not reproduced the same spectral variation on Ryugu17. The fact that we still have not reproduced the exact trend as seen on Ryugu may reflect that we do not have the appropriate starting material yet, suggesting that the returned sample will be somewhat different from what we have in the meteorite collection.The solar-wind irradiation dose of Facet A is <20% of that experienced by the average surface. This suggests that Facet A takes more than 5 times longer to be space weathered by the solar wind than typical locations on Ryugu. Because Ryugu’s color variation is the ongoing process induced by space weathering, the space weathering timescale for Ryugu’s surface is on the order of the surface’s exposure time, which was estimated as ~1024) than C-type asteroids because reddening is a relatively recent event on Ryugu. An asteroid family whose members share similar orbital elements is formed by catastrophic disruption of the original parent body. The observed variation of b-x (0.40–0.86 µm) spectral slope is −0.17 µm−1 for the north pole region compared to 0.10–0.12 µm−1 for the global average and Otohime Facet C. The spectral slope range of the inner main belt asteroids in the Eulalia and Polana families are within the same range as the variation observed on Ryugu29, while the Erigone family members show more variation in the redder range. This suggests that Ryugu could have originated from either the Polana or Eulalia families. Furthermore, the spectral properties of Otohime’s blue facets are similar to those of Polana and Eulalia’s blue global average spectra . The upturn in the UV-blue region is a peculiar feature highlighted in the spectra of (3200) Phaethon31 and (101955) Bennu32  Phaethon, the target of the DESTINY + Mission6 suggests the presence of Mg-rich phyllosilicates. Thus, Ryugu might contain an appreciable amount of both Fe- and Mg-rich phyllosilicates. Although there is no good spectral and physical match to our well-investigated samples in terms of darkness3, shallow 2.7-µm6 and 0.7-µm bands, and low thermal inertia42, here the hydrothermal history is discussed based on our current knowledge. Nevertheless, it is highly possible that Ryugu’s composition contains materials not sampled in our meteorite collections.The 0.7-µm band absorption for Ryugu is indicative of Fe-bearing phyllosilicates. In contrast, a peak OH-band at 2.72 µm6 (1) aqueously altered and thermally metamorphosed carbonaceous chondrite (ATCC including CY) material, (2) incipiently altered inter planetary-dust-particle-like, or cometary material. The 0.7-µm band absorption is closely related to the amount of Fe-rich phyllosilicates10. Up to now, the 0.7-µm feature has been detected in spectra of CM chondrites, ATCCs and only one CR chondrite44. However, the CR chondrites usually display a much higher reflectance45. The range of the 0.7-µm band depth for CM chondrites and ATCCs are 0.5–6% and <2%, respectively44, which overlaps the observed 0.7-µm band depth of 0–3% on Ryugu. Thus, Ryugu’s parent body was likely formed in a similar environment as CM chondrites in terms of water/rock ratio to produce the 0.7-µm band absorption. Nevertheless, a weak OH-band absorption, ~8%, and its short peak wavelength at 2.72 µm is not common among the general CM chondrite feature, although some highly aqueously altered CM chondrites also show a sharp OH-band peak close to 2.7 µm46. This OH-band feature can be reproduced by a peak shift toward shorter wavelengths by partial dehydration44. Moreover, thermal metamorphism is also known to decrease the near-ultraviolet absorption as well16. Such a mild dehydration process could have resulted in a flat near-ultraviolet spectrum, a weak 0.7-µm band absorption, and a decreased OH-band absorption with peak position at 2.72 µm. Thus, scenario 1 with the connection to aqueously altered and thermally metamorphosed CM-like material is more plausible. Because phyllosilicates are completely decomposed at 870–970 K (600–700 °C)47, the maximum temperature that Ryugu’s parent body experienced must have been lower than this level. Moreover, laboratory experiments on CM chondrites reported that although the 0.7-µm band absorption due to Fe-rich phyllosilicates drastically decreases at ~570–670 K (300–400 °C)20, these phyllosilicates are usually transformed into highly desiccated and disordered intermediate phases at 570–870 K (300–600 °C)50. Thus, the heating temperature for Ryugu might be lower than 670 K (400 °C). Otherwise, heterogeneous heating and dehydration might also contribute to the preservation of 0.7-µm band absorption. Besides, the fresh material on Ryugu has a negative slope in the visible wavelength range (0.40–0.95 µm) and a positive slope in the near-infrared wavelength range (1.9–2.6 µm), suggesting a concave shape from visible to near-infrared reflectance spectrum. A weak 0.7-µm feature associated with a broad absorption feature around 1 µm is often observed in the visible to near-infrared spectra of ATCCs and B-type asteroids51. The concave shape of the spectra around 1 µm can be indicative of either olivine, Fe-bearing phyllosilicates43, and/or magnetite51. Alternatively, a currently unsampled carbonaceous chondrite that experienced intensive hydration and subsequent heating would produce Ryugu’s unique spectral features. To summarize, the weak 2.7-µm band absorption and presence of the 0.7-µm feature could be explained by aqueous and thermal alteration of a CM-like precursor (scenario 1), which corresponds to Stage II in the thermal metamorphic stages defined by ref. 50 or an unsampled hydrated carbonaceous chondrite. CYs are not the best candidate for Ryugu’s material because they are typically heated >770 K (>500 °C) and are highly dehydrated52.The presence and degree of both 0.7-µm and 2.7-µm features on Ryugu allows us to constrain the parent body thermal history and water abundance. Previous global studies of Ryugu suggest two scenarios for the main composition of Ryugu:54. Our results support that Ryugu’s parent body may have formed under similar water/rock ratio conditions as CM chondrites, 0.3– 0.653, but subsequently experienced thermal metamorphism to a maximum of 570–670 K (300–400 °C). The uniformity in visible and near-infrared spectra6 implies either that there were no large displacements or differentiation between rock and ice particles in the parent body even at high temperatures, or that dust and water were convecting as a mud ball55. However, possible heterogeneity in the parent body has been suggested by the Hayabusa2 Thermal Infrared Imager (TIR)42 and ONC-T measurements in anomalous regions, although the portion of Ryugu covered by these regions is very minor. Very high density and bright materials on Ryugu35 might have been caused by hot pressing occurring over only a minor part of parent body, possibly in its center. Ryugu possesses an extremely porous uppermost layer which displays low reflectance and extremely low thermal inertia56. These properties suggest that Ryugu’s parent body might have been ~100 km in diameter and had layers with different degrees of thermal metamorphism  is sensitive to the accretion age of the parent body. In contrast, heating due to impact is less likely because it would accompany with impact-induced compaction4, which is inconsistent with Ryugu’s highly porous boulder structure observed on Ryugu41. A planetesimal would have required a relatively high ratio of 26Al to achieve temperatures sufficiently high to cause thorough dehydration, corresponding to early accretion, 2–2.5 Ma post Calcium-Aluminum-rich Inclusions57, while non-ATCC CM chondrites record low temperature aqueous reactions , corresponding to 3–4 Ma by isotopic dating58. It should be noted that aqueous alteration temperatures among non-ATCC vary over a wide range 250–550 K61. Besides, ATCCs in the meteorite collections are also reported to have experienced a variety of heating temperatures, 470 K to >1000 K61  provides constraints on the formation conditions of water-rich carbonaceous asteroids in the early solar system. Although the Fe-bearing phyllosilicates of Ryugu suggests a similar water/rock ratio to CM chondrites, the formation timing of Ryugu’s B-type parent body, possibly Polana or Eulalia, might be earlier than CM chondrites’ parent bodies.Oxygen isotopic compositions suggests that CI chondrites were formed with higher water/rock ratios than CM chondritesism Fig. . The det14. The digital count images were converted into radiance factor (I/F) images by the radiometric calibration64. All the I/F images were photometrically corrected to the standard geometry of  =  based on the photometry model by ref. 26 with the shape model of SFM_3M_v20200815 and SPICE kernels (see “Data availability”), where i, e, and α are incidence, emission, and phase angles, respectively. The shape model was derived in the same manner as ref. 34 but using all the image from proximity operations around the asteroid. We used pixels with i < 70°, e ≤ 70°, and I/F > 0.005 in order not to introduce large error by photometric correction and shadow regions. The b (0.48 µm)- to- x (0.86 µm) spectral slope was calculated as done by ref. 3. The bluest regions are found in the pole regions.Global spectral slope in Supplementary Fig. 12. Because the stray light can be reproduced according to the spacecraft attitude, the stray light could be removed using the stray light template obtained by the same spacecraft attitude during cruising phase. After the stray light removal, other calibrations were conducted as same as the global dataset. Note that after the touchdowns (TDs) of Hayabusa2 on Ryugu, the optical efficiency of ONC-T was degraded by ~7% and 2–5% at v band, respectively64. Because the effect is not strongly dependent on the wavelength <1%, we could still evaluate the spatial distribution of spectral indices using normalized spectra obtained from the images after touchdowns64. There is a known issue that spectral sensitivity changes for the close encounter images, especially by scattered light inside of the hood of ONC-T. However, it is possible to evaluate spatial relative spectral variability. To obtain plausible spatial relative variations, we factored the images so that the median normalized I/F value in the images matched the I/F obtained by the global observation by ref. 3 and ref. 26. After registration of images to the v-band image, the spectral indices, such as 0.7 µm-band absorption and b-to-x spectral slope, were calculated. The 0.7 µm-band absorption dw is calculated asRn indicates the reflectance for the band filter and coefficients are wavelength weights. Reflectance values were weighted by the wavelength. When the value is positive, there is absorption at the w band. The ambiguity of absolute 0.7-µm absorption measurement from the sensitivity calibration of ONC-T is 1.6%12. This ambiguity is due to the spectral uncertainty of standard stars used for the radiometric calibration. However, spatial relative variation can be measured more accurately based on the onground and inflight signal-to-noise assessments. More specifically, the signal-to-noise ratio for one pixel is 200 for the reference temperature at −30 °C12. At the reference temperature, shot noise is the dominant factor and is random. Thus, we can reduce this random noise by 8 pixel by 8 pixel or 15 pixel by 15 pixel binnings to obtain better SNR, leading the detection capability of 0.7-µm to σ ~0.2% and σ ~0.1%, respectively, which is sufficient to evaluate the 0.3–0.7% spatial difference of 0.7-µm band absorption. To extract high accuracy spectra in Fig. Following the global observations at an altitude of 20 km, Hayabusa2 conducted closer approaches to the pole region at an altitude of 5 km on 28 February, 1 March, and 26 October 2019. Their phase angles were 17°, 17°, and 34°, respectively. The images were taken by ONC-T with 7-color filters . Some images were contaminated by stray light from the radiator, which was strongly related to the attitude of the spacecraft with respect to the Solar radiation vectorThe near infrared spectrometer (NIRS3) also observed the south pole on 27 February 2019, 27 July 2019, and 26 October 2019, where all three facets of Otohime boulder were observed, and the north pole on 26 July 2019. For these observations, we extracted NIR spectra from both inside the region of interest  and outside the region of interest as a standard for comparison. All four observations listed above have been acquired at different phases of the proximity phase (Supplementary Table i)/(D/1au)2, where i is incidence angle with respect to the Sun and D is distance between Ryugu and the Sun, . Depending on the season, solar photon dose distribution can vary due to the small obliquity of the rotational pole. Figure We calculated the average photon dose, as solar irradiation index, in the current orbit and pole orientation. We used the SPICE toolkit with SPICE kernels to calculate the values. The shape model constructed SHAPE_SFM_200k_v20200815 was used. The relative photon dose for each polygon at any specific time can be calculated as cos experienced by a wide range of thermal metamorphism up to temperature of total dehydration and recrystallization at >1020 K. Several studies have estimated the heating temperature of ATCCs using X-ray diffraction and electron probe microanalysis61, while Raman spectra of their insoluble organic matter has also been used to classify the degree of heating63. Figure 61 compared with Ryugu’s estimated heating temperature. Thermal metamorphism was classified into four stages by50. Stage I samples do not show heat-induced mineralogical changes in the X-ray diffraction patterns due to the low temperature <570 K (< 300 °C) they experienced. Stage II samples do not show either serpentine reflection nor secondary olivine and major phases include partially dehydrated amorphous phyllosilicates at the heating temperature of 570–770 K (300–500 °C). Stage III samples start to contain low-crystalline secondary olivine and no serpentine in the X-ray diffraction pattern at the heating temperature of 770–1020 K (500–750 °C). Fe-rich phyllosilicates are completely dehydrated at this stage. Stage IV samples are completely dehydrated and consist entirely of anhydrous minerals, such as recrystallized secondary olivine at the temperature >1020 K (>750 °C).Carbonaceous chondrites that show evidence of aqueous alteration followed by thermal metamorphism were first termed as ATCCs bySupplementary InformationPeer Review FileDescription of Additional Supplementary FilesSupplementary Movie 1Supplementary Movie 2


Access to effective communication is critical to the conversations that occur at end-of-life and represents an unaddressed need within palliative care. These challenges may disproportionately affect persons with dementia (PWD). Hearing loss is one of the most common comorbidities among PWD and is independently associated with neuropsychiatric symptoms. However, relatively little is known about the potential impact of hearing loss on PWD at end-of-life. We examined last month of life (LML) data from 971 proxies of deceased PWD from the National Health and Aging Trends Study (2011-2020). Hearing difficulty was associated with increased anxiety/sadness in PWD, χ2(1)=4.596, p=.032, such that 65.6% of persons with hearing difficulty reported anxiety/sadness in the LML. Binary logistic regression found that hearing difficulty was significantly associated with increased anxiety/sadness . Interventions that optimize communication for PWD may be a meaningful approach to improving the end-of-life experience.


Spinal cord injury (SCI) leads to severe impairment in cardiovascular control, commonly manifested as a rapid, uncontrolled rise in blood pressure triggered by peripheral stimuli—a condition called autonomic dysreflexia. The objective was to demonstrate the translational potential of noninvasive transcutaneous stimulation (TCS) in mitigating autonomic dysreflexia following SCI, using pre-clinical evidence and a clinical case report. In rats with SCI, we show that TCS not only prevents the instigation of autonomic dysreflexia, but also mitigates its severity when delivered during an already-triggered episode. Furthermore, when TCS was delivered as a multisession therapy for 6 weeks post-SCI, the severity of autonomic dysreflexia was significantly reduced when tested in the absence of concurrent TCS. This treatment effect persisted for at least 1 week after the end of therapy. More importantly, we demonstrate the clinical applicability of TCS in treatment of autonomic dysreflexia in an individual with cervical, motor-complete, chronic SCI. We anticipate that TCS will offer significant therapeutic advantages, such as obviating the need for surgery resulting in reduced risk and medical expenses. Furthermore, this study provides a framework for testing the potential of TCS in improving recovery of other autonomic functions such lower urinary tract, bowel, and sexual dysfunction following SCI.The online version contains supplementary material available at 10.1007/s13311-021-01034-5. Spinal cord injury (SCI) disrupts crucial communication between spinal and supraspinal autonomic neural circuits, resulting in severely impaired cardiovascular control . CardiovDespite the detrimental consequences, recovery of cardiovascular function following SCI remains an underexplored research avenue when compared with motor function. Moreover, the majority of pre-clinical interventions have failed to demonstrate clinical efficacy . FurtherThe ability of electrical interfaces to activate disconnected neuronal circuits has gained overwhelming attention in recent years. Epidural stimulation of the injured spinal cord has shown restoration of voluntary motor control in completely paralyzed humans  as well We have demonstrated that non-invasive transcutaneous stimulation (TCS) of the spinal cord can ameliorate orthostatic hypotension in individuals with SCI . Howevern = 13) was utilized for acute TCS experiments and groups 2, 3, and 4 (n = 10/group) were used in the long-term TCS experiments.The procedures were performed in compliance with the Canadian Council on Animal Care guidelines, with protocols approved by the Animal Care Committee at the University of British Columbia . Forty-three adult (~ 300 g), male Wistar rats  received a complete transection at the T3 spinal segment and were divided across four groups . With the rat placed in a supine position, an inguinal skin incision was made to expose the femoral artery. The pressure-sensing tip of the telemeter was inserted and secured in the femoral artery, followed by skin closure using 4-0 sutures.Autonomic dysreflexia was induced via colorectal distension (CRD) using a balloon-tipped catheter . Beat-by-beat BP and heart rate (HR) were recorded using an analog-to-digital converter . The balloon was inflated with 2 mL of air over 10 s, remaining inflated for 60 s. The difference of systolic and diastolic BP (SBP and DBP) and HR between baseline and the peak value during distension was calculated and averaged across two trials per rat.Group 1 rats received no TCS until 6 weeks after SCI when the acute, real-time effect of TCS was tested. Stimulations  were delivered using a Model 2100 Isolated Pulse Stimulator (A-M systems) via cathode  placed at the mid-dorsal surface at the T7 level. Anode  was placed ventrally along the femur  were quantified. Local skin temperature and core body temperature were recorded via a skin probe  and a rectal thermometer , respectively.TCS was delivered as a multi-session therapy starting at 5 days post-SCI and continuing for 6 weeks. Stimulations were delivered for 30 min  as two 15-min periods separated by 5 min. Rats were randomly allocated to either alternate day TCS  or daily TCS  or no TCS (group 4) groups. One rat died post-surgery, resulting in t tests. Baseline hemodynamics and autonomic dysreflexia severity between chronic TCS groups was compared via one-way ANOVA (repeated measures were used for comparison within a group at different timepoints), followed by Tukey’s test for multiple comparisons. Proportion of rats with arrhythmia events was compared using the Fisher’s exact test, followed by Pearson chi-square test for pairwise comparisons. Frequency of arrhythmia events were compared across groups using the Kruskal-Wallis test, followed by Dunn’s test for multiple comparisons. Skin and rectal temperatures were compared using one-way repeated measures ANOVA. Data are reported as mean ± standard deviation (SD) with statistical significance at p < 0.05.Baseline hemodynamics at rest and autonomic dysreflexia severity within acute TCS group were compared via two-tailed, paired A 37-year-old man with a chronic (3 years) motor-complete SCI  at the fourth cervical (C4) level was assessed across three laboratory visits. The participant provided written informed consent. This case study was approved by the University of British Columbia Clinical Ethics Board. The ability of TCS to prevent  and interrupt  autonomic dysreflexia was tested across visits.Beat-by-beat BP was measured via finger photoplethysmography  corrected to brachial BP  throughout examinations. HR was recorded via 3-lead electrocardiography . Skin temperature beneath the cathode was monitored using a temperature probe . HR, BP, and skin temperature were sampled at 1000 Hz using an analog-to-digital converter.Digital anorectal stimulation (DARS) is a routine procedure to initiate a bowel routine and has previously been employed to trigger controlled elevation in BP . DARS waTCS was delivered as continuous pulses  using an isolated bipolar constant current stimulator . Current was applied at the T7/8 spinous processes using a circular cathode with a diameter of 30 mm  placed on the skin Fig. . Two 5 ×The magnitude of the change in hemodynamic responses to DARS was calculated as the difference between the average 1 min baseline and the peak value obtained during DARS. Values are displayed as median Δ change and range. Percentage change was calculated to contextualize the magnitude of the differences between TCS OFF and TCS ON.p = 0.02). There was no lasting effect of acute TCS on BP .Interestingly, when TCS was off, the insertion of a deflated balloon-tipped catheter into the rectum also caused elevation in resting BP Fig. c, e and p = 0.0002; Fig. p < 0.0001; Fig. p = 0.0029; Fig. The efficacy of acute TCS to interrupt autonomic dysreflexia was tested by initiating TCS during ongoing CRD in group 1 Fig. a. CRD trBeat-by-beat BP and HR were measured at three timepoints after the cessation of 6-week alt. day or daily TCS. The resting hemodynamics remained largely unaffected by long-term spinal cord stimulations Table . Althougp < 0.0001; day 3, p = 0.0003; and day 7, p = 0.0002; Fig. p = 0.0019; day 3, p = 0.008; and day 7, p = 0.014; Fig. p = 0.10; day 3, p = 0.003; and day 7, p = 0.009; Fig. p ≤ 0.017) and that there were no differences between the two treatment groups (p ≥ 0.46).Cardiovascular assessments were performed on 1, 3, and 7 days following cessation of TCS Fig. a–i. Group = 0.03; Fig. p = 0.013). The frequency of arrhythmia events was also different across groups . No difference was seen between the two treatment groups (p = 0.90).Nine out of nine animals in the control group showed cardiac arrhythmia events during autonomic dysreflexia compared with 5/10 animals in each of the treatment groups  and a reduction in HR (−4 ± 1 bpm), characteristic of autonomic dysreflexia .The present study shows that acute TCS is an effective strategy for mitigating debilitating episodes of autonomic dysreflexia, with potentially permanent effects achieved via long-term stimulation. Interestingly, alternate day TCS demonstrates similar efficacy as daily TCS, which could be clinically meaningful in reducing the required number of participants’ visits. Long-term TCS also ameliorated cardiac arrhythmias, demonstrating a secondary benefit of substantial clinical importance . FinallyVarious pre-clinical approaches have been tested to mitigate autonomic dysreflexia. These broadly include (a) reducing aberrant sprouting of nociceptive sensory afferents , 28, (b)Spinal cord stimulation, via invasive means, has shown remarkable potential in improving cardiovascular function in individuals with SCI. Most studies have been focused on mitigating hypotension  following SCI –17, withDespite obvious methodological and biophysical differences, both TCS and epidural stimulation share remarkable mechanistic similarities. EMG evidence showing a high degree of congruency in evoked potentials suggests that both methods stimulate common neural correlates . MechaniA limitation of this study is the lack of detailed information on the type of cardiac arrhythmia observed during autonomic dysreflexia episodes. Since cardiac arrhythmias were identified in retrospect, ECG recordings were not available in support of the BP data. However, a previous study has shown identical BP traces in rats with SCI in response to CRD and has confirmed arrhythmia as atrioventricular blocks using ECG . Future Despite the unanswered questions, electrical neuromodulation is among the most promising treatments for SCI. In addition to highlighting the need for more mechanistic studies, the present study warrants longitudinal clinical investigations for the safety and efficacy of TCS in cardiovascular dysfunction, with possible permeation into the recovery of other crucial autonomic functions, e.g., gastrointestinal and genitourinary systems.Supplementary file1 (PDF 517 KB)Supplementary file2 (PDF 526 KB)Supplementary file3 (PDF 534 KB)Supplementary file4 (PDF 543 KB)Supplementary file5 (PDF 543 KB)Supplementary file6 (PDF 543 KB)Supplementary file7 (PDF 543 KB)Supplementary file8 (PDF 543 KB)Supplementary file9 (PDF 526 KB)Below is the link to the electronic supplementary material.


Musical hallucinations are a particular type of auditory hallucination in which the patient perceives instrumental music, musical sounds, or songs. Musical hallucinations are associated with acquired hearing loss, particularly within the elderly. Under conditions of reduced auditory sensory input, perception-bearing circuits are disinhibited and perceptual traces released, implying an interaction between peripheral sensory deficits and central factors related to brain dysfunction.A 71-year-old Caucasian man with hearing loss complained of memory difficulties and resting tremor of the right upper limb in the previous 2 years. He already had difficulties in instrumental activities of daily life. Neurological examination showed Parkinsonian signs and hypoacusia. Neuropsychological examination identified deficits in executive functions and memory tests. Brain computerized tomography and nuclear magnetic resonance scans showed mild cortical and subcortical atrophy. The clinical diagnosis of possible dementia with Lewy bodies was established. Five years later, the patient began complaining of musical hallucinations. There had been no previous change in medication. An otorhinolaryngologist diagnosed age-related hearing loss and prescribed bilateral hearing aids. After using the hearing aids, the patient did not hear the songs any longer, only some tinnitus, described as a whistle. However, at the same time, the patient started experiencing visual hallucinations he never had before.To our knowledge, the immediate shift of hallucinations from one sensory modality to another sensory modality when perception is improved has not been previously described. This report emphasizes the interaction between brain pathology and sensory deficits for the genesis of hallucinations, and reinforces the theory that attention and control networks must couple properly to the default mode network, as well as integrate and select adequately peripheral signals to the somatosensory cortices, in order to keep a clear state of mind.The clinician should bear in mind and let the patient know that improving one sensory modality to ameliorate hallucinations may sometimes paradoxically lead to hallucinations in a different sensory modality. Musical hallucinations are a particular type of auditory hallucinations in which the patient perceives instrumental music, musical sounds, or songs. Patients may have preserved insight regarding the unreality of the phenomenon, and in this case the term musical hallucinosis should be more appropriate. Musical hallucinations have been labelled Oliver Sacks’ syndrome after the British neurologist and author of the book Musicophilia . MusicalWe describe the case of a patient with dementia with Lewy bodies (DLB) and age-related hearing loss in whom the musical hallucinations shifted to visual hallucinations after correction of hearing deficit with hearing aids.A 71-year-old Caucasian man complained of memory difficulties and resting tremor of the right upper limb in the previous 2 years. He had difficulty learning new tasks like using a different mobile phone. His wife took care of his medication. He still bought the newspaper and did simple shopping in the neighborhood with the aid of a shopping list, but no longer handled financial or other important matters. There were neither hallucinations nor clear clinical fluctuation at this time. Regarding personal history, the patient suffered from controlled arterial hypertension and diabetes mellitus, angina pectoris, obstructive sleep apnea, benign prostatic hyperplasia, and major depression. He also had cataract surgery in the left eye, as well as hearing loss. Neurological examination showed positive Myerson’s sign, tongue tremor, resting tremor, and cogwheel rigidity of the right arm, mild dystonic posture of the right hand, Parkinsonian gait with mild alteration of postural reflexes, and writing tremor, and confirmed the hypoacusia. Neuropsychological examination  and was Five years later, the patient began complaining of auditory hallucinations, exclusively of musical choral nature, folk songs, nursery rhymes, well-known religious hymns, and even a popular football chant. These songs were present all the time, and were only to a certain extent attenuated by environmental noise. The patient initially thought the music was being played outside, but came to realize it was an odd phenomenon somehow generated in his brain. The patient was moderately upset and would like to be relieved, but did not attribute any frightening or persecutory meaning to the symptoms. There had been no change in levodopa, rivastigmine, antidepressant, or other medication before the musical hallucinations appeared. The psychiatry consultant prescribed low-dose risperidone (1 mg daily), but the patient became deeply sedated with urinary retention. Because of the auditory symptoms, the patient looked for the opinion of an otorhinolaryngology specialist, who diagnosed age-related hearing loss and prescribed bilateral hearing aids. Remarkably, after using the hearing aids, he did not hear the bothering songs any longer, only some tinnitus, described as a whistle. Even when he temporarily removed the hearing aids, the songs remained absent. However, at the same time, the patient began having visual hallucinations for the first time, namely he would see small spiders everywhere. Clozapine (6.25 mg daily) was initiated, with noticeable improvement of these visual hallucinations. Unfortunately, the general condition of the patient declined, he entered a nursing home, and died 1 year later.The present clinical case of a patient with DLB and age-related hearing loss illustrates the immediate shift from auditory hallucinations to visual hallucinations when bilateral hearing aids were used. To our knowledge, the immediate shift of hallucinations from one sensory modality to another sensory modality when perception is improved has not been previously described.possible DLB, namely the presence of dementia plus a core clinical feature, Parkinsonism, and eventually reached the criteria for probable DLB, by developing visual hallucinations [The patient now reported fulfilled initially the criteria for inations . Visual inations . Auditorinations . The preinations .Musical hallucinations may improve when hearing loss is overcome by cochlear implantation. However, the procedure can paradoxically trigger or aggravate these hallucinations . The plaA comment on the pharmacological treatment of musical hallucinations is worthwhile. Different drugs have been tried for the treatment of musical hallucinations, namely antipsychotic and antiepileptic drugs, with variable results, essentially on the basis of individual case reports . The patIn conclusion, improving patients’ sensory deficits is advisable; however, the clinician should bear in mind and let the patient and caregiver know that improving one sensory modality to ameliorate hallucinations may sometimes paradoxically lead to hallucinations in a different sensory modality.


Glaucoma, the leading cause of irreversible blindness, is a heterogeneous group of diseases characterized by progressive loss of retinal ganglion cells (RGCs) and their axons and leads to visual loss and blindness. Risk factors for the onset and progression of glaucoma include systemic and ocular factors such as older age, lower ocular perfusion pressure, and intraocular pressure (IOP). Early signs of RGC damage comprise impairment of axonal transport, downregulation of specific genes and metabolic changes. The brain is often cited to be the highest energy-demanding tissue of the human body. The retina is estimated to have equally high demands. RGCs are particularly active in metabolism and vulnerable to energy insufficiency. Understanding the energy metabolism of the inner retina, especially of the RGCs, is pivotal for understanding glaucoma’s pathophysiology. Here we review the key contributors to the high energy demands in the retina and the distinguishing features of energy metabolism of the inner retina. The major features of glaucoma include progressive cell death of retinal ganglions and optic nerve damage. Therefore, this review focuses on the energetic budget of the retinal ganglion cells, optic nerve and the relevant cells that surround them. Glaucoma, one of the leading causes of irreversible blindness, affects more than 70 million people worldwide. It is a heterogeneous group of diseases characterized by progressive retinal ganglion cell loss (RGCs). This leads to structural and functional damage to the optic nerve, visual loss, and blindness . GlaucomRisk factors for the onset and progression of primary open-angle glaucoma (POAG), the most common form of glaucoma, include systemic and ocular factors, such as age, ocular perfusion pressure, and intraocular pressure (IOP).Elevated IOP is one of the main risk factors across different types of glaucoma . ReducinConsiderable effort has been dedicated in previous studies to elucidate the pathology of glaucoma and to identify the cascade of structural and functional alterations in RGCs that eventually lead to their apoptosis . Early sThe brain is one of the highest energy-demanding tissues of the human body. It consumes 20% of the energy supply while comprising only about 2% of the body weight ,13. The Retinal ganglion cells (RGC) possess an exceedingly active metabolism and are particularly vulnerable to energy insufficiency . TherefoBlood flow, oxygen supply, glucose utilization, and mitochondrial function are all important factors in considering energy metabolism and are all tightly interlinked with neuronal function and survival in the retina. Increased IOP and age, the other two main risk factors of glaucoma, are both directly correlated with increased ROS and impaired mitochondrial function ,21. NumeHere we review the key contributors to the high energy demands in the retina and the distinguishing features of energy metabolism of retinal neurons. The major features of glaucoma include progressive cell death of retinal ganglions and optic nerve damage . The focThe retina is not a structurally or functionally unified organ, and it is the most complex of the ocular tissues. The neuronal component of the retina is composed of six types of neurons: photoreceptors (rods and cones), bipolar cells, horizontal cells, amacrine cells and retinal ganglion cells (RGCs) . The ret+ levels and the lactate dehydrogenase (LDH) activity, are low in the inner retina [The metabolic and energy needs of the retina have been assumed to be met by glucose, as the retina is part of the CNS, and the brain relies almost exclusively on glucose ,31. Enerr retina ,35,36.There is also a substantial portion of the energy produced through oxidation by the retina (around 65%) was not derived from glucose . PhotoreGLUT) present on both BRB facilitates glucose passage to the retina [GLUT1 is the major glucose transporter present in the retina. In humans, expression of GLUT1 is reported in both the retinal capillary endothelial cells and the retinal pigment epithelium [Retinal neurons rely more on a ready supply of glucose than glial-derived lactate for their energy production . Blood-de retina ,42. GLUTGlycolysis is an anaerobic process, which breaks down six-carbon monosaccharides through a series of enzyme-catalyzed reactions that yield two molecules of three-carbon compound pyruvates. During glycolysis, glucose in the retina can be converted into pyruvate and then transported into the mitochondria and fully oxidized, or in anaerobic conditions, pyruvate is converted into lactate, yielding substantially less ATP. The majority (~80%) of the glucose supplied to the avascular outer retina by the choroid is converted into lactate via glycolysis, in comparison to the vascularized inner retina, where only 20% of glucose supplied by the retinal circulation is converted to lactate ,37.High lactate production usually occurs when oxygen is limited. German physiologist Otto Heinrich Warburg noticed that cancerous tissue tended to divert glycolytic metabolites towards biosynthesis rather than towards oxidative phosphorylation, therefore, produce ATP via incomplete glucose oxidation despite the presence of oxygen ,44. ThisIt is not fully understood why normal tissue relies on aerobic glycolysis over oxidative phosphorylation of glucose. A possible explanation for the Warburg effect in the retina is that due to the mitochondria’s localization to the inner segment, the outer segment is forced to rely on aerobic glycolysis . This spThe cell types that carry out aerobic glycolysis in the normal adult retina are yet to be determined. The photoreceptors are assumed to be the primary site of aerobic glycolysis in the retina, as they possess enzymes for aerobic glycolysis and produce a certain quantity of lactate under physiological conditions ,49. MüllNevertheless, the purpose of aerobic glycolysis in the retina, its cell origin and relevance to photoreceptor and their regulation require to be further studied.The energetic advantage of oxidative phosphorylation (OXPHOS) in mitochondria far outweighs that of glycolysis aerobic, as per molecule of glucose yields only 2 molecules of net ATP via the glycolytic pathway and 36 molecules of ATP in the mitochondria.The retina is one of the most oxidative tissues in the body. Oxygen consumption reflects mitochondrial activity and its production of ATP. The inner segments of photoreceptors have a very high oxidative metabolism, but since the rest of the photoreceptor has no mitochondria, the outer half of the retina does not have an extraordinarily high metabolic rate . Oxygen Cytochrome c oxidase and the terminal complex (complex IV) of the electron transport chain in the inner mitochondrial membrane is a major regulation site for oxidative phosphorylation ,55. In gThe specific mediators that link neuronal metabolism with retinal angiogenesis in the developing eye and retinal disease remain largely unknown. However, it is becoming more evident that the metabolic needs of the neural retina profoundly influence the vascular network that supplies oxygen and nutrients .Some of the energy-consuming functions of neurons comprise the synthesis of proteins, the loading, release, recycling, and turnover of neurotransmitter molecules, active transport of macromolecules and organelles along microtubules between the cell bodies and their dendrites and especially axons ,61,62,63+ pumped out in exchange for 2 K+ brought into the cell [The most energy-consuming function of neurons by far appears to be the active transport of ions against their concentration and electrical gradients ,65,66. Athe cell . It servthe cell .As the distribution pattern of cytochrome c oxidase reflects the regions of energy production in the retina, the differential distribution of Na+K+ATPase denotes the reductions in energy demand.The Na+K+ATPase is densely localized in the inner segments of photoreceptor cells, the outer plexiform layer, and the nerve fiber layer, whereas the inner plexiform layer and ganglion cells have moderate levels of this enzyme .The biggest ATP demand in the retina comes from photoreceptors and the retinal pigment epithelium (RPE) . PhotoreCytochrome c oxidase, as well as Na+K+ATPase, are also densely localized in the retinal nerve fiber layer, where the ganglion cell axons are unmyelinated, which denotes a certain level of depolarizing and repolarizing activities ,75. The Neuronal energy demands are met by a tightly coupled and adaptive vascular network that supplies oxygen and nutrients like glucose, which both contribute to the final yield of ATP in mitochondria . A decreRetinal vessels are precisely regulated to optimize blood supply to meet the large metabolic needs of the retina without interfering with the visual pathway .The mature retina in humans and other primates is supplied by two vascular networks. The outer half of the retina, including the outer plexiform and outer nuclear layers, the photoreceptors, and the retinal pigment epithelium is supplied by choriocapillaris; the inner half of the retina is supplied by the inner retinal vasculature originates from branches of the central retinal artery (CRA), which in turn is a branch of the ophthalmic artery. The vasculature in the inner retina is further layered in plexuses that form a retinal neurovascular unit .The outer retina’s oxygen needs are met predominantly from the choroidal circulation, and the oxygen needs of the inner retina are met from the retinal circulation .Retinal circulation is characterized by a low-level flow and high levels of oxygen extraction . It has The IOP is elevated above ocular perfusion pressure, which leads to global ischemia with obstruction of both the retinal and uveal circulation, as evidenced by whitening of the iris and the fundus. The high IOP ischemia model characteristically injures the inner retina to a much greater extent than the outer retina .The potential role of impaired blood flow to the optic nerve as a cause of glaucoma has been discussed since the 19th century. A plethora of evidence has accumulated since then; the vast majority of published studies dealing with blood flow report reduced ocular perfusion in glaucoma patients compared with normal subjects. The reduction of blood flow and its velocities in the retina, choroid and ONH in glaucoma patients has been demonstrated using different detection methods ,94,95. GET-1) and angiotensin II, which are vascular constricting factors. Altered NO activity and ET-1 expression are documented in glaucoma patients in different studies [The major cause of this reduction is rather vascular dysregulation . Autoreg studies ,105,106.The capacity of autoregulation may become less potent, or may completely fail, in glaucoma leading to the tissue being under-perfused . EvidencRetinal neurons are the most sensitive and critical cells in the eye analogs to neurons in the brain. Other than tightly regulated hemodynamics and delivery of oxygen and metabolic substrates, intact blood-retinal barriers (BRB) are also essential requirements for the maintenance of optimal retinal structure and function . The twoThe blood-retinal barrier restricts nonspecific transport between the neural retina and the circulating blood, therefore, maintains a stable microenvironment for the neuronal cells ,110. It The inner BRB is similar to the blood–brain barrier; a functional neurovascular structure comprises the complex tight junctions of retinal capillary endothelial cells, pericytes and astrocyte foot processes ,114.The inner BRB efficiently supplies nutrients to the retina and removes endobiotic and xenobiotics from the retina to maintain a constant milieu in the neural retina . Just liRecent studies have shown that mitochondria in endothelial cells have a crucial role in maintaining the blood–brain barrier and BRB . InhibitThe outer BRB is formed at the retinal pigment epithelial (RPE) cell layer by the tight junctions between the RPE cells ,120. UnlThe optic nerve head (ONH) describes the point for the ganglion cell axons exiting the globe through the lamina cribrosa. The ONH is predominately supplied by branches of the posterior ciliary artery (PCA) and recurrent choroid arteriole with the superficial nerve fiber layer supplied by branches of the central retinal artery ,125. VenThe optic nerve head remains the point at which retinal ganglion cell axons are most vulnerable to the effects of increased intraocular pressure or ischemia; the blood flow at the optic nerve head is delicately regulated to maintain the supply of oxygen and nutrients to the RGC axons .Evidence accrued over the decades suggests that dysfunctional regulation of ocular blood flow contributes to glaucomatous optic neuropathy and plays a prominent role in glaucoma processes . In the Retinal ganglion cells (RGC), the neurons that selectively die in glaucoma, possess an exceedingly active metabolism and are particularly vulnerable to energy insufficiency . RGCs arLike most neurons, RGCs are polarized into dendritic and axonal compartments that are connected to the cell body. Signal inputs are collected by the dendrites, and output is distributed from the cell body via axons . Each suPrevious studies in animal models of glaucoma also suggest that RGCs may not all be uniformly affected; diverse RGC types respond to IOP elevation at different time-scales and to varying extents . DegenerThe most recent estimate of the number of distinct RGC types found in the mammalian retina is around 30, with more than half of these types definitively identified . HoweverThere also has been debate in the field as to whether RGCs with large somata and axons are more vulnerable, with definitive conclusions still in progress because of the wide diversity of RGC types . While tEach subcellular component of the RGC is remarkably different in terms of structure, function and extracellular environment . Rather In the following sections, we divide the RGC into the four subcellular components: (1) RGC somata located, (2) RGC dendrites and their synapses, (3) mon-myelinated axons at nerve fiber layer and at the ONH, and (4) myelinated axons in the orbit and the cranial region, which are located within the optic nerve. The distinguishing energy metabolic features and response to physiological and pathological challenges of each compartment are discussed, respectively .There is a large number of studies on quantitative measurements of energy production in the retina. However, measurements specifically targeting the metabolism of RGCs remain sparse. Different techniques have been utilized to reflect the pattern of energy consumption and distribution in different subcellular components of RGCs, such as the distribution of mitochondria, the expression of cytochrome oxidase and the presence of neuroglobin.Nonetheless, each technique also has its own technical limitations, and these are only the indices of metabolism but not necessarily linearly related to oxygen consumption. It is currently not possible to tell the exact changes in energy utilization in glaucoma. The lack of specific knowledge about energy consumption and distribution in RGC subcellular components is a limitation in our analysis of glaucoma.All RGC compartments are critically dependent on the cell body for the biogenesis of organelles. All organelles within an RGC are synthesized in the cell body and then transported to targeted sites. The functional activity and survival of RGC axons and dendrites are dependent upon the RGC somata . Injury RGC bodies are located in the RGC layer. The RGC layer has a rich blood supply ,149. MitOne RGC transmits the information from numerous photoreceptors to the brain; its cell body is significantly larger compared to other neurons in the retina. It is speculated that RGCs with larger somata and axons may be selectively vulnerable to IOP elevation . When coRGC dendrites receive inputs from bipolar cells, which convey signals from photoreceptors and from amacrine cells that branch in the inner plexiform layer (IPL) . The inpComparing to other capillary networks in the retina, the networks supplying the IPL have a smaller capillary diameter, less capillary density values and a complex three-dimensional configuration . Such stAxonal degeneration of retinal ganglion cells (RGCs) and apoptotic death of their cell bodies are observed clinically in glaucoma patients. Abnormal swelling and accumulations of mitochondria in RGC axons have been identified following prolonged IOP elevation . It has Axons of RGCs connect the eye with the brain; they are under considerable metabolic stress in both health and disease states . It is wMitochondria are distributed asymmetrically along optic nerve axons with regional organelle concentrations correlating closely with the local energy demands; the distribution and localization of mitochondria along RGC axons are critical for normal function ,172. HisNerve Fiber Layer (NFL)The nerve fiber layer is the inner retinal layer of unmyelinated ganglion cell axons. Due to the lack of salutatory conduction, their energy demands are unusually high. There is a regional layer of a capillary network called the radial parapapillary capillary plexus, which runs in parallel with the NFL axons to supply specifically the bundles ,177,178.Notwithstanding, the density of the inner retinal vasculature that is to sustain the high metabolic demands is constrained by the requirement for relative optical transparency.2.Axons at ONHThe delicate metabolic balance between energy demands and energy delivery places non-myelinated axons in the NFL in a vulnerable position to a range of disruptions that led to energy exhaustion and eventual functional failure, particularly hypoxic and ischemic insults .2.Axons3.Myelinated Axons in the Orbit and Cranial Region (Optic Nerve)Nerve fibers travel from the optic nerve head through a sieve-like structure called the lamina cribrosa into the extraocular space. In vitro tracing of individual axon paths in the human, optic nerve head has shown that some axons do not take a direct course through the lamina cribrosa (LC) . Some axJust posterior to scleral laminar, axons are wrapped by oligodendrocytes as they enter the retrolaminar part of the optic nerve . MyelinaThe axons that form the optic nerve have an average diameter of 1 mm but can range from 0.7 to 10 μm in diameter . The smaThe exact mechanisms leading to apoptosis in glaucoma are unclear. However, it is clear, other than retinal ganglion cells and their axons; the apoptosis also results in the destruction of supporting glial cells leading to a characteristic excavation of the ONH . HypoxicGlial cells protect and support the retinal ganglion cell axons in passing from the eye to the brain. The larger vessels of the inner retinal vasculature lay in the innermost portion of the retina, close to the inner limiting membrane. Their walls are in close spatial relationship with glial cells, mainly astrocytes, which constrain the vessels to the inner retina and maintain their integrity ,195. As The astrocyte-neuron lactate shuttle (ANLS) hypothesis is proposed by Pellerin and Magistretti et al. . They prWhile glutamate induced a robust metabolic response in astrocytes (decreased ATP levels and glucose uptake stimulation), GABA does not couple inhibitory neuronal activity with glucose utilization .Whether RGCs utilized lactate from glia cells as fuel is unclear. There is evidence of widespread lactate dehydrogenase (LDH) activity throughout the retina. The activity is predominantly derived from LDH-B in the inner retina. It is demonstrated that the oxygen-regulated expression of LDH-B is opposite and complementary to that of LDH-A . In bothThe high energy demands of the retina render it vulnerable to energy insufficiency. The inner retina is particularly susceptible to impaired energy metabolism due to its optical function. The energy demands of the neurons are tightly coupled with their functional activity. Each compartment of RGC is located in different retinal layers, therefore, different extracellular environments and have specific energy requirements. The energy homeostasis of RGC is complex and dependent upon a delicately regulated system to meet regional metabolic demands. The energetics of RGC compartments and their support system is important for helping us better understand the pathogenesis of glaucoma and develop a potential treatment for this leading cause of blindness throughout the globe.


Vorticity random fields of turbulent flows  are singled out as the main dynamic variables for the description of turbulence, and the evolution equation of the probability density function (PDF) of the vorticity field has been obtained. This PDF evolution equation is a mixed type partial differential equation (PDE) of second order which depends only on the conditional mean (which is a first-order statistics) of the underlying turbulent flow. This is in contrast with Reynolds mean flow equation which relies on a quadratic statistics. The PDF PDE may provide new closure schemes based on the first-order conditional statistics, and some of them will be described in the paper. We should mention that the PDF equation is interesting by its own and is worthy of study as a PDE of second order. There arbulence ,11). In The main contribution of the present work is the partial differential equation (PDE) for the PDF of the vorticity , which will be derived in the main body of the paper. The PDF PDE is highly nonlinear; however, the most striking aspect is that the PDF PDE for the vorticity depends only on one single first-order statistical characteristic of the turbulent flow. More precisely, we identify the main statistical characteristic needed for the PDF PDE with the conditional mean function of the increment of the vorticity given the current vorticity:The paper is organized as follows. In §2, several notions and notations together with several standard assumptions about fluid dynamic random fields will be introduced, and the main result, namely the PDF PDE for vorticity, will be derived. In §§3 and 4, the theoretical foundation, based on our PDF PDE for vorticity, will be laid for the purpose of modelling various turbulent flows. In §5, we propose the most direct way of modelling PDF of the vorticity by specifying the conditional mean function  (a)The following conventions are used throughout the paper. Firstly Einstein’s convention on summation on repeated indices through their ranges is assumed, unless otherwise specified. If The velocity vector field will be denoted by . 2In this paper, we regard the vorticity of an incompressible turbulent flow as the main dynamic variable. The goal of this section is to derive the evolution equation for the PDF of the vorticity of an incompressible turbulent flow. (a)Let We make the following technical assumptions.First, we assume that both Our second technical assumption is to impose certain regularity on the distribution of the vorticity. At each point To state our third assumption, we first notice thatThe third technical assumption is about the regularity of the conditional average function In the remainder of the paper, we will work with a turbulent flow for which the three assumptions listed above are satisfied. (b)In this section, we derive the main result of the paper, that is a PDE which the PDF of the vorticity must satisfy.Under the assumptions and notations established in §2a, suppose the PDFof the vorticity is smooth inand has finite moments, that isfor everyThensatisfies the following PDE:whereis the Laplacian with respect to the space variableandare given as in (2.5) and (2.6),andLet equation  and obtan, using , we may by using  when h iequation  now follThe PDE , althougIf all coefficients  PDF PDE . The goo (c)As an application of the PDF PDE obtained in the previous subsection, we address a long-standing question in turbulence about the distribution of turbulent flows. It has been conjectured and verified by measurements over many years cf. ,12) that that12])Consider an incompressible viscous (with viscosityturbulent flow with vorticitySuppose (1)the mean vorticity is constant at any instance, (2)is weakly isotropic in the sense thatfor allandand (3)the distribution ofis Gaussian.Then the distribution ofis independent ofSince  PDF PDE  must sat. 3There is a significant simplification in PDF PDE for an inviscid ‘turbulent’ flow, although such turbulence may not exist in nature. For inviscid fluid flows, the velocity en as in  and  where the dataandare assumed as given. Assume thatandare Lipschitz continuous inuniformly inSupposeis a solution to (3.1) with continuous initial dataand supposedecays to zero sufficiently fast asThen we have the following: (1)for allthenfor alland (2)Supposefor allthenfor allandif and only iffor allandLet us define the integral curves egrating  over R3 e obtain . Converse obtain  holds, be obtain  over R3 . 4It has been pointed out in §§2 and 3, the coefficients appearing in the PDF PDE are determined by the conditional mean function fined in . The sigThe homogeneity and the isotropicity can be defined in general for random fields indexed by a space variable y Taylor . The locy Taylor ,13, a raweakly homogeneous in the sense that for every pair We may simplify the PDF PDE for turbulent flows when the vorticity random field weakly isotropic, ifWe say that the vorticity If After we have deduced the PDE , there iThe following theorem provides the foundation for modelling weakly isotropic turbulent flows based on the vorticity PDF.Consider the parabolic-transport differential equation (4.2), whereandare considered as given. Assume thatandare Lipschitz continuous in space variableuniformly inSupposeis a solution to (4.2) such thatis continuous and decays to zero sufficiently fast as (1)Iffor allandthenfor alland (2)Ifis a PDF for everyi.e. it is non-negative andfor everythen so arefor allandif and only iffor alland (3)Suppose in additionis independent ofandthen ifis a PDF for everyis also a PDF for everyand for everyThe proof is rather similar to that of theorem 3.1, so we only provide an outline. Let egrating ,(∂∂t+Bi. 5In this and the next sections, several simple models based on our PDF equation for modelling vorticity distributions in turbulence are discussed. Clearly, the most straightforward way for modelling the distribution of vorticity is to assign the conditional mean function For practical reasons which will be clarified in our computations below, the simplest yet not trivial model for  PDF PDE  vanish iThe solution to  has a niThe initial PDF entation , we obtaIf equation  leads toFor this case, the mean vorticity . 6In this section, we propose another model for the PDF of the vorticity, based on the heat flow method, in which the conditional mean function The solution to equation  is givenThe previous SDEs have explicit solutions:Therefore, if d Y into  we haveAs in the previous section, the initial vorticity is assumed to be of the formrding to ,f(w;x,tLet us discuss a special case where If fined by .A similar discussion applies to the model where fined by .Suppose again the initial vorticityIf We may conclude that this model provides some nice features of the propagation of the vorticity which may be helpful for the understanding of the energy dissipation in turbulence, and we will explore this in a separate work.