Population Of Fibers Research Articles

Ecosystem engineers enter the city: Habitat characteristics influencing the distribution of Eurasian beavers Castor fiber in a human-transformed landscape

In recent decades, the population of the Eurasian beaver Castor fiber has increased significantly, and from near extinction the species has become widespread again over large part of its former range. However, the recovery of the beaver population is giving rise to increasing numbers of human-beaver conflicts in areas inhabited by humans. The key challenge of beaver population management is, therefore, to identify habitat characteristics that determine the presence of the species in the human-dominated landscape, including urban areas. Based on a large-scale inventory of beavers conducted in one of the most densely populated regions of Europe, we show that the factors enhancing habitat suitability for beavers at the landscape scale are the increasing cover of meadows and surface waters, and the total length of watercourses. Although beavers avoid built-up areas, 13% of all recorded sites were located in the most densely populated regions, and the local habitat features that favour the presence of beavers in an urban landscape are the increasing cover of forests, meadows and surface waters, the total length of watercourses and the total length of roads. This indicates that patches of natural or semi-natural vegetation persisting along watercourses located in the vicinity of communication routes constitute a habitat for beavers entering the most urbanized areas. The beaver is currently expanding into western and southern Europe, but the species’ future distribution will include highly transformed urban areas. To limit human-beaver conflicts, predictions of beaver distributions in human-dominated landscapes should be used in urban and landscape planning.

Depicting the anatomy of the gyral white matter: ubi sumus? quo vadimus?

Abstract A cerebral gyrus is made up of an external layer of folded cortex and an inner core of white matter. The architecture of the core has specific features that make it distinct from the white matter of the deep brain regions. Limited externally by the grey matter that covers the top of the gyrus and the neighbouring sulci, this gyral white matter is made up of a mix of fibre populations with multiple directions and destinations. The presence of densely packed fibres with multiple crossings, the proximity to the cortex and the existence of inter-regional and inter-individual variations make the task of depicting this microanatomy extremely challenging. The topic is, however, of paramount relevance for both fundamental and applied neurosciences. This fibre colocalization is crucial for the functional role of each cerebral region and is key to clinical manifestations in cases of parenchymal damage. As track tracing, imaging and dissection are based on different biological or physical principles, it is natural for their results to sometimes be different, but they are often complementary. As the amount of available information increases, it becomes fragmented due to the multiplicity of methods, target phenomena and studied species. In this scoping review, we present the key concepts and map the primary sources of evidence regarding identifying the fibre pathways that compose the gyral white matter, enabling the discussion of avenues for future research. The general pattern in which these pathways are distributed in the gyral white matter was detailed, and the main variations as a function of brain topography were explained and illustrated with typical examples.

Age-related changes in the healthy adult visual pathway: evidence from diffusion tensor imaging with fixel-based analysis.

Fixel-based analysis (FBA) is anew method that overcomes the technical limitations of diffusion tensor imaging (DTI) by enabling the characterization of multiple fiber populations within avoxel, and provides biologically meaningful indicators. This study aimed to explore age-related changes in the visual pathway in healthy adults and to observe differences in imaging quality between data collected using different b‑values. In this prospective cross-sectional study, brain DTI scans which were collected with more than six uniformly distributed gradient directions and higher b‑values (up to 2000 s/mm2) than traditional DTI were performed in 72healthy adults across the adult lifespan (20-79years). After image preprocessing, FBA was used to process the dataset. At the same time, conventional DTI metrics were also calculated. Pearson's correlation analysis showed that DTI parameters of white matter (optic nerve, optic chiasma, optic tract, and optic radiation) in the optic pathway were correlated with age. FA values were negatively correlated with age, while MD/AD/RD showed apositive correlation (P < 0.05). FBA showed that the index including FD/FC/FDC tended to decline with age (P < 0.05). Linear regression analysis showed alinear relationship between DTI metrics of the dataset collected by b‑values of 1000 and 2000 s/mm2 (P < 0.05). FBA provides auseful method to assess age-related changes in the visual pathway, which is sensitive to diffusion. In addition, the b‑value influences DTI parameters and signal-to-noise ratio of the image.

Impact of high consistency enzymatic hydrolysis and defibration drying on cellulose fiber pore characteristics

AbstractThe purpose of this study is to examine the hornification of enzymatically hydrolyzed high consistency softwood kraft pulp in an experimental defibration dryer. This device dries pulp under turbulent conditions which can prevent interfiber bonding and produce a separated fiber population. This is useful in certain applications, such as composites, which require dry, unbonded pulp fibers. In this study, we examine how fibrillated pulps behave in the dryer with respect to pore expansion in hydrolysis and collapse in drying (hornification). It was found that the endoglucanase cocktail increased the micro-, meso-, and macropore volumes as a function of hydrolysis time. Drying decreased the pore volumes of each size category, with the biggest changes in the macropore region. The pulp with the highest swelling after hydrolysis had the lowest swelling after drying. The mesopores that were formed in hydrolysis were somewhat preserved after drying. After drying, unfibrillated pulp had good fiber separation, while the highly fibrillated samples formed sub-millimeter, spherical particles.

Pharmacognostic standardization and machine learning-based investigations on Akebia quinata and Akebia trifoliata.

Currently, Akebiae Caulis is being used in clinical practice, but there are few reseaches on its different varieties. To ensure the accuracy and effectiveness of clinical practice,this study distinguished the Akebia quinata (Thunb.) Decne. and Akebia trifoliata (Thunb.) Koidz, using organoleptic evaluation, microscopic observation, fluorescence reaction, physicochemical properties, thin-layer chromatography, IR spectroscopy, HPLC, four machine learning models, and in vitro antioxidant methods. Analysis of the powders of these two varieties using optical microscopy revealed the presence of starch granules, cork cells, crystal fibers, scalariform vessels, and wood fibers. Scanning electron microscopy revealed the presence of scalariform vessels, pitted vessels, wood fibers, and calcium oxalate crystals. Several tissues, including the cork layer, fiber population, cortex, phloem, pith, xylem, and ray, were found in the transverse section. In addition, thin-layer chromatography was used to identify two components: oleanolic acid and calceolarioside B; 11 common peaks were identified in 15 batches of SAQ and 5 batches of SAT by using HPLC. Support vector machine, BP neural networks, and GA-bp neural networks were able to predict 100% accurately of the different origins of stem of Akebia quinate (Thunb.) Decne (SAQ) and Akebia trifoliata (Thunb.) Koidz (SAT). Extreme learning machine achieved a correct rate of 87.5%. Meanwhile, Fourier-transform infrared spectroscopy fingerprint identified nine characteristic absorption peaks of the secondary metabolites of SAQ and SAT. 2,2-Diphenyl-1-1-picrylhydrazyl experiment revealed that the IC50 values of SAQ and SAT extracts were 155.49 and 128.75 μg/ml, respectively. For the 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) assay, the IC50 value of SAT extract was found to be 269.24 μg/ml, which was lower than that of SAQ extract (IC50 = 358.99 μg/ml). This study successfully used different methods to differentiate between A.quinata (Thunb.) Decne. and A.trifoliata (Thunb.) Koidz., to help decide on which type to use for clinical application.

Fiber-specific age-related differences in the white matter of healthy adults uncovered by fixel-based analysis

Diffusion magnetic resonance imaging studies often investigate white matter (WM) microstructural degeneration in aging by probing WM regions that exhibit negative age associations of fractional anisotropy (FA). However, WM regions in which FA is unassociated with age are not necessarily “spared” in aging. Besides the confound of inter-participant heterogeneity, FA conflates all intravoxel fiber populations and does not allow the detection of individual fiber-specific age associations. In this study of 541 healthy adults aged 36–100 years, we use fixel-based analysis to investigate age associations among each “fixel” within a voxel, representing individual fiber populations. We find age associations of fixel-based measures that indicate age-related differences in individual fiber populations amid complex fiber architectures. Different crossing fiber populations exhibit different slopes of age associations. Our findings may provide evidence of selective degeneration of intravoxel WM fibers in aging, which does not necessarily manifest as a change in FA and therefore escapes notice if conventional voxel-based analyses are relied upon alone.

Unraveling multi-fixel microstructure with tractography and angular weighting.

Recent advances in MRI technology have enabled richer multi-shell sequences to be implemented in diffusion MRI, allowing the investigation of both the microscopic and macroscopic organization of the brain white matter and its complex network of neural fibers. The emergence of advanced diffusion models has enabled a more detailed analysis of brain microstructure by estimating the signal received from a voxel as the combination of responses from multiple fiber populations. However, disentangling the individual microstructural properties of different macroscopic white matter tracts where those pathways intersect remains a challenge. Several approaches have been developed to assign microstructural properties to macroscopic streamlines, but often present shortcomings. ROI-based heuristics rely on averages that are not tract-specific. Global methods solve a computationally-intensive global optimization but prevent the use of microstructural properties not included in the model and often require restrictive hypotheses. Other methods use atlases that might not be adequate in population studies where the shape of white matter tracts varies significantly between patients. We introduce UNRAVEL, a framework combining the microscopic and macroscopic scales to unravel multi-fixel microstructure by utilizing tractography. The framework includes commonly-used heuristics as well as a new algorithm, estimating the microstructure of a specific white matter tract with angular weighting. Our framework grants considerable freedom as the inputs required, a set of streamlines defining a tract and a multi-fixel diffusion model estimated in each voxel, can be defined by the user. We validate our approach on synthetic data and in vivo data, including a repeated scan of a subject and a population study of children with dyslexia. In each case, we compare the estimation of microstructural properties obtained with angular weighting to other commonly-used approaches. Our framework provides estimations of the microstructure at the streamline level, volumetric maps for visualization and mean microstructural values for the whole tract. The angular weighting algorithm shows increased accuracy, robustness to uncertainties in its inputs and maintains similar or better reproducibility compared to commonly-used analysis approaches. UNRAVEL will provide researchers with a flexible and open-source tool enabling them to study the microstructure of specific white matter pathways with their diffusion model of choice.

Stocking density, ambient temperature, and group size affectsocial behavior, productivity and reproductivity of goats- A review.

The stocking density (animal/area, SD) is one of the significant factors that influence the welfare and performance of animals. However, there are discrepancies in the recommended SD for fiber, meat, and dairy goats, which means farming practices and welfare standards for goats should be better defined. Therefore, this review article sheds light on 1) some differences between goats and sheep. 2) the geographical distribution of fiber, meat type, and dairy goat populations. 3) effects of interaction between SD and group size on social, feeding, and aggressive behaviors. 4) the effects of SD on meat and milk production. 5) the relationship between SD and reproductive performance. In conclusion, the larger space allowance with access to an outdoor yard can improve species-specific behaviors and meat and milk yield. Moreover, goats are more sensitive to high SD (less than 3 m2/ goat), especially during the last stage of the gestation period. Allowing optimal floor space for each breed is important to avoid the undesired behavioral response. Conclusively, improving the housing aspects, including floor space and enrichment tools, would assist in implementing welfare-economic production standards for goats.

High-frequency longitudinal white matter diffusion- and myelin-based MRI database: Reliability and variability.

Assessing the consistency of quantitative MRI measurements is critical for inclusion in longitudinal studies and clinical trials. Intraclass coefficient correlation and coefficient of variation were used to evaluate the different consistency aspects of diffusion- and myelin-based MRI measures. Multi-shell diffusion and inhomogeneous magnetization transfer data sets were collected from 20 healthy adults at a high-frequency of five MRI sessions. The consistency was evaluated across whole bundles and the track-profile along the bundles. The impact of the fiber populations on the consistency was also evaluated using the number of fiber orientations map. For whole and profile bundles, moderate to high reliability of diffusion and myelin measures were observed. We report higher reliability of measures for multiple fiber populations than single. The overall portrait of the most consistent measurements and bundles drawn from a wide range of MRI techniques presented here will be particularly useful for identifying reliable biomarkers capable of detecting, monitoring and predicting white matter changes in clinical applications and has the potential to inform patient-specific treatment strategies.

Fluorescent microspheres can affect in vitro fibrinolytic outcomes.

Hemostasis is the cessation of bleeding due to the formation of a blood clot. After the completion of wound healing, the blood clot is typically dissolved through the natural process of fibrinolysis, the enzymatic digestion by plasmin of the fibrin fibers that make up its structural scaffold. In vitro studies of fibrinolysis reveal mechanisms regulating these processes and often employ fluorescent microscopy to observe protein colocalization and fibrin digestion. In this study, we investigate the effects of labeling a fibrin network with 20 nm diameter fluorescent beads (fluorospheres) for the purpose of studying fibrinolysis. We observed fibers and 2-D fibrin networks labeled with fluorospheres during fibrinolysis. We found that the labeling of fibrin with fluorospheres can alter fibrinolytic mechanisms. In previous work, we showed that, during lysis, fibrin fibers are cleaved into two segments at a single location. Herein we demonstrate that fibrinolysis can be altered by the concentration of fluorospheres used to label the fibers, with high concentrations of fluorospheres leading to very minimal cleaving. Furthermore, fibers that are left uncleaved after the addition of plasmin often elongate, losing their inherent tension throughout the imaging process. Elongation was especially prominent among fibers that had bundled together due to other cleavage events and was dependent on the concentration of fluorophores used to label fibers. Of the fibers that do cleave, the site at which they cleave also shows a predictable trend dependent on fluorosphere concentration; low concentrations heavily favor cleavage locations at either end of fibrin fiber and high concentrations show no disparity between the fiber ends and other locations along the fiber. After the initial cleavage event bead concentration also affects further digestion, as higher bead concentrations exhibited a larger population of fibers that did not digest further. The results described in this paper indicate that fluorescent labeling strategies can impact fibrinolysis results.

Computational modeling of the human compound action potential.

The auditory nerve (AN) compound action potential (CAP) is an important tool for assessing auditory disorders and monitoring the health of the auditory periphery during surgical procedures. The CAP has been mathematically conceptualized as the convolution of a unit response (UR) waveform with the firing rate of a population of AN fibers. Here, an approach for predicting experimentally recorded CAPs in humans is proposed, which involves the use of human-based computational models to simulate AN activity. CAPs elicited by clicks, chirps, and amplitude-modulated carriers were simulated and compared with empirically recorded CAPs from human subjects. In addition, narrowband CAPs derived from noise-masked clicks and tone bursts were simulated. Many morphological, temporal, and spectral aspects of human CAPs were captured by the simulations for all stimuli tested. These findings support the use of model simulations of the human CAP to refine existing human-based models of the auditory periphery, aid in the design and analysis of auditory experiments, and predict the effects of hearing loss, synaptopathy, and other auditory disorders on the human CAP.

A computational modelling framework for assessing information transmission with cochlear implants

Computational models are useful tools to investigate scientific questions that would be complicated to address using an experimental approach. In the context of cochlear-implants (CIs), being able to simulate the neural activity evoked by these devices could help in understanding their limitations to provide natural hearing. Here, we present a computational modelling framework to quantify the transmission of information from sound to spikes in the auditory nerve of a CI user. The framework includes a model to simulate the electrical current waveform sensed by each auditory nerve fiber (electrode-neuron interface), followed by a model to simulate the timing at which a nerve fiber spikes in response to a current waveform (auditory nerve fiber model). Information theory is then applied to determine the amount of information transmitted from a suitable reference signal (e.g., the acoustic stimulus) to a simulated population of auditory nerve fibers. As a use case example, the framework is applied to simulate published data on modulation detection by CI users obtained using direct stimulation via a single electrode. Current spread as well as the number of fibers were varied independently to illustrate the framework capabilities. Simulations reasonably matched experimental data and suggested that the encoded modulation information is proportional to the total neural response. They also suggested that amplitude modulation is well encoded in the auditory nerve for modulation rates up to 1000 Hz and that the variability in modulation sensitivity across CI users is partly because different CI users use different references for detecting modulation.

Optic radiations representing different eccentricities age differently.

The neuralpathways that carry information from the foveal, macular, and peripheral visual fields have distinct biological properties. The optic radiations (OR) carry foveal and peripheral information from the thalamus to the primary visual cortex (V1) through adjacent but separate pathways in the white matter. Here, we perform white matter tractometry using pyAFQ on a large sample of diffusion MRI (dMRI) data from subjects with healthy vision in the U.K. Biobank dataset (UKBB; N= 5382; age 45-81). We use pyAFQ to characterize white matter tissue properties in parts of the OR that transmit information about the foveal, macular, and peripheral visual fields, and to characterize the changes in these tissue properties with age. We find that (1) independent of age there is higher fractional anisotropy, lower mean diffusivity, and higher mean kurtosis in the foveal and macular OR than in peripheral OR, consistent with denser, more organized nerve fiber populations in foveal/parafoveal pathways, and (2) age is associated with increased diffusivity and decreased anisotropy and kurtosis, consistent with decreased density and tissue organization with aging. However, anisotropy in foveal OR decreases faster with age than in peripheral OR, while diffusivity increases faster in peripheral OR, suggesting foveal/peri-foveal OR and peripheral OR differ in how they age.

Study of histochemical characterizations of skeletal muscle fiber types in the rabbits ( Oryctolagus Cuniculus )

This project has been conducted on New Zealand White Rabbits (newborns and adults) . Biceps brachii, soleus and abdominal wall of muscles were used in this study. Fresh pieces of muscle tissues were frozen to be cut at (10 μm) thick sections by the cryostat.Skeletal musclefibre types were investigated histochemically to demonstrate myosin adenosin triphosphatase (ATPase) activity using acid and alkaline preincubation and succinate dehydrogenase ( SDHase ) activity . In this way it may be possible to recognize the fast and slow twitch muscle fibers, as well as to explore the difference in reaching maturity between different muscles of the body. The results showed that, the biceps brachii and abdominal wall muscles consist predominantly of fast fibers, whilst the soleus muscle is made up of a near homogenous population of slow fibers. The immature abdominal wall muscle showed some reversal of the mature limb muscles staining pattern of the same animal.

Characterization and applications of evoked responses during epidural electrical stimulation

BackgroundEpidural electrical stimulation (EES) of the spinal cord has been FDA approved and used therapeutically for decades. However, there is still not a clear understanding of the local neural substrates and consequently the mechanism of action responsible for the therapeutic effects.MethodEpidural spinal recordings (ESR) are collected from the electrodes placed in the epidural space. ESR contains multi-modality signal components such as the evoked neural response (due to tonic or BurstDR™ waveforms), evoked muscle response, stimulation artifact, and cardiac response. The tonic stimulation evoked compound action potential (ECAP) is one of the components in ESR and has been proposed recently to measure the accumulative local potentials from large populations of neuronal fibers during EES.ResultHere, we first review and investigate the referencing strategies, as they apply to ECAP component in ESR in the domestic swine animal model. We then examine how ECAP component can be used to sense lead migration, an adverse outcome following lead placement that can reduce therapeutic efficacy. Lastly, we show and isolate concurrent activation of local back and leg muscles during EES, demonstrating that the ESR obtained from the recording contacts contain both ECAP and EMG components.ConclusionThese findings may further guide the implementation of recording and reference contacts in an implantable EES system and provide preliminary evidence for the utility of ECAP component in ESR to detect lead migration. We expect these results to facilitate future development of EES methodology and implementation of use of different components in ESR to improve EES therapy.

Investigating a Closed Loop Neural Control System to Optimize Sacral Neuromodulation

Background and Hypothesis:Approximately 16% of the American population suffers from overactive bladder, with 25-40% of patients reporting unsatisfactory results following first line treatments. Sacral neuromodulation is a well-established, minimally invasive treatment option for several forms of bladder and bowel dysfunction that are non-responsive to first line pharmacologic or behavioral therapies. While more broadly applicable stimulus parameters are being investigated, the precise set of nerve fibers whose activity regulates optimal bladder function(s) is not known, leading to high levels of treatment variability between patients and within patients over time. We hypothesize that treatment efficacy and durability could be rapidly improved by continuously tuning the electrical stimulus waveform and pattern of stimulation to recruit the nerve fiber populations that mediate micturition.&#x0D; Experimental Approach:We aim to access the sacral (S2-4) nerves and implant a set of recording and stimulating bipolar cuff electrodes (FNC-400-V-R-C-2C-30, Micro-Leads, Somerville, MA, USA) to measure the evoked CAP of the sacral nerves at various combinations of pulse amplitude and duration. Simultaneously, we will measure changes in bladder pressure using a pressure transducer attached to a bladder catheter and amplifier. By measuring how the bladder responds to all applied nerve stimulation parameters we will be able use an Autonomous Neural Control algorithm to identify the compound nerve action potential response that produces the most robust changes in pressure.&#x0D; Results:We developed a surgical protocol, currently pending PACUC approval, that allows us to decode and encode specific CAP signatures that represent the firing activity of distinct subsets of nerve fibers, each differing in diameter, degree of myelination, activation threshold, conduction speed, and presumably function.&#x0D; Conclusion and Potential Impact:This study aims to act as proof of concept for a system that selects stimulation parameters based on fibers required to produce a desired response rather than patient tolerance to stimulation parameters, ultimately improving efficacy of sacral neuromodulation therapy.

Distinct signatures of white matter damage in cerebral small vessel disease and Alzheimer’s disease: a fixel‐based analysis study

AbstractBackgroundAlzheimer’s disease (AD) and cerebral small vessel disease (SVD) are the two main causes of age‐related cognitive decline and frequently co‐exist in memory clinic patients. White matter diffusion alterations have been described as key features of both diseases with different spatial patterns in AD and SVD. Biomarkers that capture and disentangle the effects of each disease on white matter integrity are of great need but are still lacking. Advanced diffusion MRI‐based techniques on the fixel level (fiber population within a voxel) yield promise, since one can derive measures of both fiber density and fiber bundle cross‐section (Dhollander et al., Neuroimage, 2021). In this multimodal imaging study, we assessed the ability of these fixel metrics to detect disease‐specific signatures of white matter fiber tract damage yielding the path towards personalized medicine.MethodWe included genetically defined SVD (n=73) and the full continuum of biomarker‐characterized AD from ADNI (n=34 Aβ–T–; n=19 Aβ+T–, n=18 Aβ+T+). Using multi‐shell diffusion MRI, we assessed the fiber density and fiber bundle cross‐section of six well‐established white matter fiber tracts previously shown to be damaged or related to cognitive decline in AD and SVD (see Figure 1). Using simple linear regression analyses and while controlling for intracranial volume, we determined associations between tract‐specific fixel metrics and imaging markers of SVD (white matter hyperintensity volume, lacune and microbleed count) and AD (global amyloid‐ and tau‐PET SUVR) as well as age and brain volume.ResultFiber density of all fiber tracts was strongly associated with white matter hyperintensity volume in SVD (e.g. inferior fronto‐occipital fasciculus, R2adj=73%). In contrast, fiber bundle cross‐section was highly associated with cerebral atrophy in the AD sample (e.g. corpus callosum, R2adj=36%). Of note, both fiber density and fiber bundle cross‐section were only weakly associated with amyloid‐ and tau‐PET (e.g. fiber density of uncinate fasciculus ∼ amyloid‐PET, R2adj=11%; fiber bundle cross‐section of inferior longitudinal fasciculus ∼ tau‐PET SUVR, R2adj =5%).ConclusionFiber density captures the effects of SVD on white matter integrity whereas fiber bundle cross‐section indicates tract‐specific neurodegeneration in AD. Fixel‐based analysis allows to assess disease‐specific effects of SVD and AD on white matter fiber tracts.

Distinct signatures of white matter damage in cerebral small vessel disease and Alzheimer’s disease: a fixel‐based analysis study

AbstractBackgroundAlzheimer’s disease (AD) and cerebral small vessel disease (SVD) are the two main causes of age‐related cognitive decline and frequently co‐exist in memory clinic patients. White matter diffusion alterations have been described as key features of both diseases with different spatial patterns in AD and SVD. Biomarkers that capture and disentangle the effects of each disease on white matter integrity are of great need but are still lacking. Advanced diffusion MRI‐based techniques on the fixel level (fiber population within a voxel) yield promise, since one can derive measures of both fiber density and fiber bundle cross‐section (Dhollander et al., Neuroimage, 2021). In this multimodal imaging study, we assessed the ability of these fixel metrics to detect disease‐specific signatures of white matter fiber tract damage yielding the path towards personalized medicine.MethodWe included genetically defined SVD (n=73) and the full continuum of biomarker‐characterized AD from ADNI (n=34 Aβ–T–; n=19 Aβ+T–, n=18 Aβ+T+). Using multi‐shell diffusion MRI, we assessed the fiber density and fiber bundle cross‐section of six well‐established white matter fiber tracts previously shown to be damaged or related to cognitive decline in AD and SVD (see Figure 1). Using simple linear regression analyses and while controlling for intracranial volume, we determined associations between tract‐specific fixel metrics and imaging markers of SVD (white matter hyperintensity volume, lacune and microbleed count) and AD (global amyloid‐ and tau‐PET SUVR) as well as age and brain volume.ResultFiber density of all fiber tracts was strongly associated with white matter hyperintensity volume in SVD (e.g. inferior fronto‐occipital fasciculus, R2adj=73%). In contrast, fiber bundle cross‐section was highly associated with cerebral atrophy in the AD sample (e.g. corpus callosum, R2adj=36%). Of note, both fiber density and fiber bundle cross‐section were only weakly associated with amyloid‐ and tau‐PET (e.g. fiber density of uncinate fasciculus ∼ amyloid‐PET, R2adj=11%; fiber bundle cross‐section of inferior longitudinal fasciculus ∼ tau‐PET SUVR, R2adj =5%).ConclusionFiber density captures the effects of SVD on white matter integrity whereas fiber bundle cross‐section indicates tract‐specific neurodegeneration in AD. Fixel‐based analysis allows to assess disease‐specific effects of SVD and AD on white matter fiber tracts.

Гистоморфометрическая оценка большеберцового нерва и мелких мышц стопы после внутреннего невролиза и аутогенной пластики большеберцовой порции седалищного нерва крыс

Introduction Transformations of the nerves and muscles of the distal extremities after nerve injuries at the level of the proximal segments are critical for the restoration of functions, but have not been sufficiently studied in experimental biological models. Purpose Histomorphometric evaluation of the tibial nerves and plantar interosseous muscles after internal neurolysis and autogenous plasty of the tibial portion of the sciatic nerve (SN) in rats. Materials and methods The study was performed on 21 male Wistar rats, aged 8-10 months. Series 1 (internal SN neurolysis) – n = 6. Series 2 (autogenous SN neuroplasty) – n = 8. Control – 7 intact rats. The rats were euthanized 6 months after the operation. Light microscopy and histomorphometry of transverse semithin sections of the tibial nerve at the level of the middle third of the lower leg and paraffin sections of the plantar interosseous muscles of the foot were performed. Results In series 1, endoneural vessels had increased diameters and wall thickness in the tibial nerve, but a smaller lumen compared to the norm; the dimensional characteristics of the myelinated fiber population were increased due to myelin decompactization and axonal edema; about 10 % of myelinated fibers were destructively changed. In series 2, the numerical density of the endoneural vessels of the tibial nerve was doubled in comparison with the intact one; the numerical and dimensional composition of the regenerated myelinated fibers indicated active but incomplete regeneration. The vascularization index of the plantar interosseous muscles in series 1 was close to normal, in series 2 it decreased twice, the median of muscle fiber diameters was reduced by 12.41 % (p = 0.000) and 20.96 % (p = 0.000), respectively. Muscle fibers with a diameter of more than 30 μm increased in series 2 compared to series 1. Conclusion Internal neurolysis and interfascicular autoplasty of the sciatic nerve cause multidirectional changes in the endoneural vessels of the tibial nerve, which predetermine the multidirectional nature and severity of denervation and reinnervation changes in the nerves of the lower leg and small muscles of the foot.

A Computational Model of a Single Auditory Nerve Fiber for Electric-Acoustic Stimulation

Cochlear implant (CI) recipients with preserved acoustic low-frequency hearing in the implanted ear are a growing group among traditional CI users who benefit from hybrid electric-acoustic stimulation (EAS). However, combined ipsilateral electric and acoustic stimulation also introduces interactions between the two modalities that can affect the performance of EAS users. A computational model of a single auditory nerve fiber that is excited by EAS was developed to study the interaction between electric and acoustic stimulation. Two existing models of sole electric or acoustic stimulation were coupled to simulate responses to combined EAS. Different methods of combining both models were implemented. In the coupled model variant, the refractoriness of the simulated fiber leads to suppressive interaction between electrically evoked and acoustically evoked spikes as well as spontaneous activity. The second model variant is an uncoupled EAS model without electric-acoustic interaction. By comparing predictions between the coupled and the noninteracting EAS model, it was possible to infer electric-acoustic interaction at the level of the auditory nerve. The EAS model was used to simulate fiber populations with realistic inter-unit variability, where each unit was represented by the single-fiber model. Predicted thresholds and dynamic ranges, spike rates, latencies, jitter, and vector strengths were compared to empirical data. The presented EAS model provides a framework for future studies of peripheral electric-acoustic interaction.