bioRxiv Subject Collection: Neuroscience's Journal

A positive feedback loop between sensory and octopaminergic neurons underlies nociceptive plasticity in Drosophila larvae
Adaptive modulation of nociceptive behaviour based on prior experience is essential for responding effectively to environmental threats. In Drosophila larvae, nociceptive escape behaviours are robust and stereotyped, yet emerging evidence suggests this can be modulated by experience and internal state. Here, we demonstrate that repeated activation of nociceptive sensory neurons enhances both the likelihood and intensity of nocifensive rolling, reflecting a form of behavioural sensitization. This heightened responsiveness is accompanied by a sustained increase in activity within nociceptive sensory neurons, suggesting that plasticity arises, at least in part, within the sensory compartment. We identified the neuromodulator octopamine as a critical regulator of the sensitization: signalling through the octopamine receptor OAMB is required to sustain elevated nociceptive gain, and feedback from one of octopaminergic neurons class, the ventral unpaired median (VUM) neurons, amplifies sensory neuron output. Together, these findings reveal an experience-dependent positive feedback loop in the nociceptive system, where neuromodulatory circuits tune behavioural output.

Barcoded Rabies In Situ Connectomics for high-throughput reconstruction of neural circuits
Sequencing of oligonucleotide barcodes holds promise as a high-throughput approach for reconstructing synaptic connectivity at scale. Rabies viruses can act as a vehicle for barcode transmission, thanks to their ability to spread between synaptically connected cells. However, applying barcoded rabies viruses to map synaptic connections in vivo has proved challenging. Here, we develop Barcoded Rabies In Situ Connectomics (BRISC) for high-throughput connectivity mapping in the mouse brain. To ensure that the majority of post-synaptic "starter" neurons are uniquely labeled with distinct barcode sequences, we first generated libraries of rabies viruses with sufficient diversity to label >1000 neurons uniquely. To minimize the probability of barcode transmission between starter neurons, we developed a strategy to tightly control their density. We then applied BRISC to map inputs of single neurons in the primary visual cortex (V1). Using in situ sequencing, we read out the expression of viral barcodes in rabies-infected neurons, while preserving spatial information. We then matched barcode sequences between starter and presynaptic neurons, mapping the inputs of 385 neurons and identifying 7,814 putative synaptic connections. The resulting connectivity matrix revealed layer- and cell-type-specific local connectivity rules and topographic organization of long-range inputs to V1. These results show that BRISC can simultaneously resolve the synaptic connectivity of hundreds of neurons while preserving spatial information, enabling reconstruction of neural circuits at an unprecedented scale.

Deformed Probability Estimation in Goal-Directed reinforcement learning model explains anxious-depression dimensions of psychiatric disorders
Psychiatric disorders are complex, multi-dimensional pathologies rooted in diverse cognitive processes. Computational psychiatry aims to reveal distortions in these processes through behavior modeling, providing a deeper understanding of psychiatric disorders. Previous studies, using Daws two-stage task, had linked the imbalance between habitual/model-free and goal-directed/model-based behaviors to disorders with compulsive behaviors and intrusive thoughts. The model-based component relies on the estimation of environmental probabilities. Therefore, we added a well-known deformation in subjective probability estimation to the model and this improved the model fitting. More importantly, the fitted deformation explains some variance of the anxious-depression dimension of psychiatric symptoms. The deformation parameter is aligned with the description-experience gap in decision-making literature. Our results point to subjective possibly distortion as the probable underlying cognitive process of anxiety, apathy, and depression. This study also shows that the inclusion of cognitive biases in modeling can extract the hidden aspects of behavior possibility linked to disorders. Our approach enhances the precision of computational psychiatry and provides deeper insights into the cognitive processes underlying psychiatric symptoms, paving the way for more effective, personalized therapeutic strategies.

Maturation of Dorsal Association Tracts during Preadolescence Links to Concurrent and Future Cognitive Performance and Transdiagnostic Psychopathology
Many psychiatric disorders begin during adolescence, coinciding with the rapid development of brain white matter (WM). However, it remains unclear whether deviations from normal WM maturation during this age period contribute to the development of psychopathology. In this study, we developed and validated normative models of brain age based on specific WM tracts using three large-scale developmental datasets (a total of ~10,000 subjects). We found that tract-specific deviations in WM development of association and limbic/subcortical systems were linked to concurrent cognition and psychopathology. The spatial pattern of the association system aligned closely with distributions of high-order brain networks, and with mitochondrial content and respiratory capacity. The maturation of the association system contributed significantly to better cognitive performance assessed two or three years later. Importantly, delayed WM development especially in dorsal association tracts predicted psychiatric disorders across diagnoses and disorder onset over a 2-year follow-up. By identifying tract-specific WM development during preadolescence as a predictor of cognitive capacity and psychiatric disorder risks, this study provides a valuable framework for tracking individualized brain maturation and understanding the neurobiological underpinnings of cognitive performance and transdiagnostic psychopathology.

Investigating the sensitivity of the diffusion MRI signal to magnetization transfer and permeability via Monte-Carlo simulations
Purpose: Magnetization transfer (MT) and water exchange via permeability operate on a similar spatiotemporal scale to water diffusion. In this study, we use a simulation-based approach to characterise how MT and permeability impact (1) diffusion-weighted MRI (dMRI) measurements from cylindrical substrates and (2) parameter estimation using a two-compartment model of white matter. Methods: We used Monte-Carlo simulations to model the dMRI signal inside and outside axons by simulating signals from parallel cylinders with different diameters and volume densities. We subsequently introduced membrane permeability and MT at the cylinder walls to investigate their impact on the dMRI signal. We fitted a two-compartment model to the simulated signal to produce estimates of the cylinder diameter and density. We evaluated the impact of MT and permeability by comparing the fitted diameter and density to the simulated ground truth. Results: Permeability leads to underestimation (up to 100%) of cylinder diameter and density. Specifically, by enabling isochromats to escape from restrictions and diffuse more freely, permeability makes the overall displacement profile closer to the extra-axonal displacement profile. MT had limited effects on diameter estimation but caused substantial bias (20-50%) in volume density estimates depending on the ratio of the intra-axonal and extra-axonal volume fraction. This is due to the intra-axonal and extra-axonal space having different surface-to-volume ratios and therefore different surface relaxation rates. Conclusion: Permeability and MT can considerably influence the dMRI signal. They increase the relative contribution from larger cylinders to the dMRI signal and bias microstructural parameter estimates derived from dMRI data.

Neuron-derived extracellular vesicles in plasma present a potential non-invasive biomarker for Huntingtin protein and RNA assessment in Huntington disease
Huntington disease (HD) is a neurodegenerative disease caused by a trinucleotide repeat expansion in the HTT gene encoding an elongated polyglutamine tract in the huntingtin (HTT) protein. The use of biomarkers has become a major component in preclinical studies focusing on HTT lowering strategies. Quantification of soluble mutant HTT (mHTT) in cerebrospinal fluid (CSF) has served as a pharmacodynamic readout and as potential disease progression biomarker. However, development of future assays for HTT measurement from other biofluids, such as blood, will facilitate the access to human samples since CSF collection is an invasive outpatient procedure. Brain cells, in particular neurons, secrete extracellular vesicles (EVs) that cross the blood-brain barrier and circulate in blood. Importantly, EVs have been identified to be involved in HTT export from cells to the extracellular space. However, it is unknow which vesicle subtype correlates better with HD progression. Our work investigates the potential of EVs as non-invasive sources of clinical biomarkers in liquid biopsies. We developed an optimized ultracentrifugation protocol for the purification of ectosomes and exosomes from human samples and plasma of humanized HD mouse models. Ectosomes are larger vesicles that bud from the plasma membrane of cells, whereas exosomes originate from multivesicular bodies and are afterwards released to the extracellular space. Consistent with previous published data in other model systems, ectosomes isolated from plasma of the Hu97/18 mouse model contain both wild-type (WT) and mHTT in higher levels than in exosomes. Similar results were observed in media from HD iPSC-differentiated neurons and in Hu97/18 primary neuronal cultures. Interestingly, we also found higher levels of HTT transcripts in this EV subtype. We further demonstrate that initial storage of the samples using a slow freezing protocol preserves HTT and EV protein marker levels, highlighting the importance of sample preparation for EV isolation and analysis. Our results also show that plasma contains vesicles originated from neuronal cells that can be isolated using neuron-specific markers, such as ATPase Na+/K+ transporting subunit alpha 3 (ATP1A3), allowing the evaluation of HTT levels in the brain through vesicles circulating in the blood. Overall, our results demonstrate that HTT protein measurement from EVs isolated from blood can be a potential less-invasive disease biomarker. We also demonstrate that EVs subtypes contain different HTT protein and RNA levels, important for the development of consistent and reliable biomarkers. Further characterization of neuron-specific EVs content from patient-derived biofluids will lead to the development of novel clinical biomarkers and for evaluation of therapeutic strategies.

A morphological comparison of the caudal rami of the superior temporal sulcus in humans, chimpanzees, and other great apes
For centuries, anatomists have charted the folding patterns of the sulci of the cerebral cortex in primates. Improvements in neuroimaging technologies over the past decades have led to advancements in understanding of the sulcal organization of the human cerebral cortex, yet comparisons to chimpanzees, one of humans' closest extant phylogenetic relatives, remain to be performed in many regions, such as superior temporal cortex. For example, while several posterior branches, or rami, of the superior temporal sulcus (STS) have been identified in great apes since the late 1800s, no study has yet to comprehensively identify and quantitatively compare these rami across species. To fill this gap in knowledge, in the present study, we defined the three caudal branches of the STS (cSTS) in 72 human and 29 chimpanzee brains (202 total hemispheres) and then extracted and compared the morphological (depth and surface area) properties of these sulci. We report three main findings. First, modern methods replicate classic findings that three rami of the posterior STS are unique to the hominid lineage (i.e., humans and great apes). Second, normalizing for brain size, the cSTS rami were relatively deeper in chimpanzees compared to humans. Third, the cSTS branches were relatively larger in surface area in humans compared to chimpanzees. Finally, we share probabilistic predictions of the cSTS to guide the identification of these sulci in future studies. Altogether, these findings bridge the gap between historic qualitative observations and modern quantitative measurements in a part of the brain that has expanded substantially throughout evolution and that is involved in human-specific aspects of cognition.

Starvation transforms signal encoding in C. elegans thermoresponsive neurons and suppresses heat avoidance via bidirectional glutamatergic and peptidergic signaling
Animals must continuously adapt their behavioral outputs in response to changes in internal state, including nutritional state. Here, we show that starvation induces a profound and progressive suppression of thermonociceptive behavior in Caenorhabditis elegans. The thermoresponsive sensory neurons AWCs mediate robust heat-evoked reversals over a broad range of stimulus intensities via glutamate and FLP-6 neuropeptide signaling, each covering distinct heat intensity ranges. After six hours of food deprivation, heat-evoked reversal responses are nearly abolished, independently of any external food odor cues. Prolonged food deprivation triggers a switch in AWC heat-evoked activity patterns, transitioning from a predictable, stimulus-locked response mode to a heterogeneous and stochastic regime. This switch relies on ASI neurons, proposed to work as internal state-sensing neurons. INS-32 and NLP-18 neuropeptide signals from ASI switch from a reversal-promoting to a reversal-inhibiting effect. Glutamatergic transmission from non-AWC neurons is also engaged to suppress reversals. Our findings define a circuit logic by which nociceptive responsiveness gating by internal nutritional state is linked to dynamic modulation of sensory neuron activity patterns and orchestrated by bidirectional glutamatergic and neuropeptidergic signals. More broadly, this study illustrates how sensory systems integrate metabolic information to prioritize behavioral outputs under changing physiological conditions, providing mechanistic insight into the plastic coupling between sensation, internal state, and action selection.

Shared and modality-specific brain networks underlying predictive coding of temporal sequences
Predictive coding posits that the brain continuously generates and updates internal models to anticipate incoming sensory input. While auditory and visual modalities have been studied independently in this context, direct comparisons using matched paradigms are scarce. Here, we employed magnetoencephalography (MEG) to investigate how the brain of 83 participants encodes and consciously recognises temporally unfolding sequences that acquire Gestalt-like structure over time, a feature rarely addressed in cross-modal research. Participants memorised matched auditory and visual sequences with coherent temporal structure and later identified whether test sequences were familiar or novel. Multivariate decoding revealed robust discrimination between the brain mechanisms underlying encoding and recognition of memorised and novel sequences, with sustained temporal generalisation in the auditory domain and time-specific responses in the visual domain. Using the BROAD-NESS pipeline, we identified modality-specific and supramodal brain networks. Auditory memory engaged auditory cortex, cingulate gyrus, and hippocampus, whereas visual memory involved orbitofrontal cortex and visual areas. Notably, both modalities recruited a shared network including hippocampus and medial cingulate during recognition. These findings provide compelling evidence for distinct and shared predictive learning mechanisms across sensory systems, advancing our understanding of how the brain integrates and evaluates temporally structured, Gestalt-like information.

Increased Exertion Variability is Linked to Disruptions in Effort Assessment in Multiple Sclerosis
Accurate assessment of exertion is crucial for determining whether to continue or rest during physical activity. Individuals with multiple sclerosis (MS) often report fatigue and motor impairments, yet the mechanisms underlying their assessments of effortful exertion remain poorly understood. Recent work with healthy individuals suggests that motor variability can distort judgments of effort; however, this relationship has not been explored in individuals with MS. In this study, we investigated how variability in physical exertion affects effort assessment in individuals with MS compared to healthy participants. We had participants exert varying levels of physical effort and retrospectively assess the effort they exerted. Individuals with MS exhibited increased exertion variability and tended to overreport their levels of exertion compared to healthy participants. Increased exertion variability was associated with less accurate effort assessment, and this effect was more pronounced in individuals with more advanced MS. These results suggest a possible mechanism through which motor variability may be associated with inflated perceptions of effort in MS, highlighting a potential account of why efforts feel particularly costly to those individuals living with MS and identifying a promising target for treatment and rehabilitation.

NKG2D receptor ligands are cell surface biomarkers for injured murine and human nociceptive sensory neurons
Nociceptors are primary afferent neurons that sense noxious stimuli. They can be activated by tissue injury as well as the accompanying local immune response. We have shown that following nerve injury in mice cytotoxic Natural Killer (NK) cells infiltrate the peripheral nerve and interact with stress-induced ligands of the activating receptor NKG2D (Klrk1). However, the diversity and specificity of NKG2D receptor ligands among sensory neuron subtypes, and translation of this mechanism to humans, remains unknown. We used dorsal root ganglion (DRG) neurons cultured from C57BL/6J mice of both sexes with fluorescently-labelled sensory neuron lineages (Scn10a, Mrgprd, Calca, Trpv1, Th, Thy1), as well as human induced pluripotent stem cell derived (hiPSCd)-sensory neurons after laser ablation, as in vitro models of axonal injury. We assessed expression of NKG2D ligands by quantitative polymerase chain reaction (PCR) corroborated by publicly available RNA sequencing datasets and validated with single-cell PCR. Recombinant NKG2D receptor proteins in live cell-based assays were used to reveal the subcellular membrane localisation of NKG2D ligands with quantification by a semi-automated image analysis. Functional interactions between human NK cells and sensory neurons were confirmed with co-cultures in microfluidic devices. We show that NKG2D ligands are expressed exclusively in unmyelinated DRG neurons after injury. NKG2D-receptors bound to puncta along distal neurites of injured axons enriched predominantly in Mrgprd-expressing non-peptidergic nociceptors. We observed low-level binding of human NKG2D-receptors to neurites of hiPSCd sensory neurons that increased after axonal laser ablation. Degeneration of hiPSCd sensory neurons neurites by interleukin (IL-2) primed human NK cells was prevented by an NKG2D blocking antibody. The induction and enrichment of functional NKG2D receptor ligands selectively on pathological nerve fibres could aid the diagnosis of peripheral neuropathy in chronic pain conditions, and sheds new light on the potential role of nociceptive neurons in regulating the local tissue immune microenvironment.

A deep learning framework for understanding cochlear implants
Sensory prostheses replace dysfunctional sensory organs with electrical stimulation but currently fail to restore normal perception. Outcomes may be limited by stimulation strategies, neural degeneration, or suboptimal decoding by the brain. We propose a deep learning framework to evaluate these issues by estimating best-case outcomes with task-optimized decoders operating on simulated prosthetic input. We applied the framework to cochlear implants--the standard treatment for deafness--by training artificial neural networks to recognize and localize sounds using simulated auditory nerve input. The resulting models exhibited speech recognition and sound localization that was worse than that of normal hearing listeners, and on par with the best human cochlear implant users, with similar results across the three main stimulation strategies in current use. Speech recognition depended heavily on the extent of decoder optimization for implant input, with lesser influence from other factors. The results identify performance limits of current devices and demonstrate a model-guided approach for understanding the limitations and potential of sensory prostheses.

Comprehensive characterization of human color discrimination thresholds
Discrimination thresholds reveal the limits of human perception; scientists have studied them since the time of Fechner in the 1800s. Forced-choice psychophysical methods combined with the method of constant stimuli or parametric adaptive trial-placement procedures are well-suited for measuring one-dimensional psychometric functions. However, extending these methods to characterize psychometric fields in higher-dimensional stimulus spaces, such as three-dimensional color space, poses a significant challenge. Here, we introduce a novel Wishart Process Psychophysical Model (WPPM) that leverages the smooth variation of threshold across stimulus space. We demonstrate the use of the WPPM in conjunction with a non-parametric adaptive trial-placement procedure by characterizing the full psychophysical field for color discrimination in the isoluminant plane. Each participant (N = 8) completed between 6,000 and 6,466 three-alternative forced-choice (3AFC) oddity color discrimination trials. The WPPM was fit to these trials. Importantly, once fit, the WPPM allows readout of discrimination performance between any pair of stimuli, providing a comprehensive characterization of the psychometric field. In addition, the WPPM readouts were validated for each participant by comparison with 25 probe psychometric functions. These were measured with an additional 6,000 trials per participant that were held out from the WPPM fit. The dataset offers a foundational resource for developing perceptual color metrics and for benchmarking mechanistic models of color processing. This approach is broadly generalizable to other perceptual domains beyond color.

mGluR4-Npdc1 complex mediates α-synuclein fibril-induced neurodegeneration
Fibrils of misfolded -synuclein (-syn) accumulate in Parkinson's disease and other synucleinopathies, spreading between cells to template further misfolding and drive neurodegeneration. -syn fibril entry into healthy neurons is recognized as a key step in the disease process but remains ill-defined mechanistically. Here, we comprehensively assessed the membrane proteome for binding of -syn fibrils. Expression cloning identified mGluR4 and Npdc1 as plasma membrane proteins expressed by substantia nigra neurons capable of supporting high affinity -syn fibril binding. Moreover, mGluR4 and Npdc1 cellular signaling functions were titrated by the presence of extracellular fibrillary -syn. While striatal -syn fibril injection led to nigral dopamine neuron loss in wild type mice, deletion of either Grm4 or Npdc1 provided protection of dopamine neurons. We observed mGluR4 and Npdc1 to form a complex that regulates mGluR4 signaling. Cultured neurons lacking both Grm4 and Npdc1 fail to bind -syn fibrils, to accumulate phosphorylated -syn and to lose synapses. Transheterozygous Grm4, Npdc1 mice showed protection from nigral neuron loss after striatal -syn injection, demonstrating genetic interaction between the two binding proteins. On a transgenic -syn A53T background, double Grm4, Npdc1 heterozygosity robustly increased mouse survival, motor function and spinal motoneuron number. Thus, a cell surface mGluR4-Npdc1 complex participates in -syn neurodegeneration.

Dual-feature selectivity enables bidirectional coding in visual cortical neurons
Sensory neurons are traditionally viewed as feature detectors that respond with an increase in firing rate to preferred stimuli while remaining unresponsive to others. Here, we identify a dual-feature encoding strategy in macaque visual cortex, wherein many neurons in areas V1 and V4 are selectively tuned to two distinct visual features---one that enhances and one that suppresses activity---around an elevated baseline firing rate. By combining neuronal recordings with functional digital twin models---deep learning-based predictive models of biological neurons---we were able to systematically identify each neuron's preferred and non-preferred features. These feature pairs served as anchors for a continuous, low-dimensional axis in natural image similarity space, along which neuronal activity varied approximately linearly. Within a single visual area, visual features that strongly or weakly activated individual neurons also had a high probability of modulating the activity of other neurons, suggesting a shared feature selectivity across the population that structures stimulus encoding. We show that this encoding strategy is conserved across species, present in both primary and lateral visual areas of mouse cortex. Dual-feature selectivity is consistent with recent anatomical evidence for feature-specific inhibitory connectivity, suggesting a coding strategy in which selective excitation and inhibition increase the representational capacity of the neuronal population.

Pharmacological inhibition of all known major inward cationic currents does not block the induction of spreading depolarizations
Spreading depolarization (SD) is a wave of profound cellular depolarization that propagates across central nervous system tissue and causes a near-complete collapse of ionic gradients. Implicated in neuropathologies including seizures, migraine with aura, traumatic brain injury, and stroke, SD is experimentally induced in animals by electrical stimulation, mechanical injury, hypoxia, elevated extracellular potassium, and various other techniques. Despite extensive research, the mechanisms underlying SD initiation remain unclear. Prior research in rodents found that simultaneously blocking sodium, calcium, and glutamatergic (AMPA and NMDA) channels prevents SD induction whereas inhibiting any two of these three currents is insufficient. This suggests that SD induction could be a product of overstimulation of any single known inward cationic current. However, some researchers propose that SD induction occurs via an unknown SD channel. To further explore the role of known inward cationic currents in SD induction, we applied high potassium to two biological models, namely zebrafish and mice. First, we developed a novel ex vivo zebrafish model to assess SD induction in the optic tectum. Using KCl microinjection and DC local field potential recordings, we found that inhibition of sodium, calcium, and glutamatergic channels significantly decreased SD amplitude but never blocked SD induction in the zebrafish optic tectum. Similar pharmacological experiments in hippocampal mouse slices (CA1 subregion) also confirmed that SDs persist despite the same pharmacological cocktail. These findings suggest that additional mechanisms beyond sodium, calcium, and glutamatergic signaling contribute to SD induction, supporting the hypothesis that a currently unknown channel is critical in SD physiology.

Generation and characterization of a tamoxifen-inducible, Cre driver rat for transgene expression in microglia
Microglia are the resident immune cells of the central nervous system (CNS) and display diverse functions under both physiological and pathological conditions. The past decade has seen burgeoning interest in microglia function, with a variety of transgenic tools developed for specific genetic manipulation of microglia in various injury, disease, and developmental models. Although the majority of models have been developed in mice, the ability to manipulate microglia in rats provides additional advantages to studying microglial function in the brain especially related to complex behavior. Using BAC transgenesis, our lab has created a transgenic rat (Cx3cr1-CreERT2) that expresses a tamoxifen inducible Cre recombinase (CreERT2) under control of the microglial/macrophage specific fractalkine C-X3-C Motif Chemokine Receptor 1 (Cx3cr1) promoter. In mice, CreERT2 and other transgenes have been expressed in microglia using the Cx3cr1 promoter, however, this is the first demonstration in rats. Importantly, these rats exhibit similar cognitive behaviors compared to their wildtype (WT) controls. Microglial specificity of inducible Cre expression was confirmed by breeding the novel Cx3cr1-CreERT2+/- rat with a previously reported double floxed inverse open reading frame (DIO)-mCherry+/- reporter rat to show tamoxifen inducible mCherry expression that colocalizes with the microglial marker Iba1. In addition, we utilize flow cytometry to demonstrate time and Cre dependent differences in recombination of Cx3cr1+ cells in the spleen, peripheral blood, and brain at two- and eight-weeks post-tamoxifen treatment. Overall, we have created a novel transgenic rat model for researchers to employ in understanding microglial and peripheral immune cell function in rats.

Fusiform Cells in the Dorsal Cochlear Nucleus Change Intrinsic Electrophysiological Properties and Morphologically Remodel Their Basal Dendrites with Age
Age-related hearing loss (ARHL) is the most common cause of sensorineural hearing loss. The cochlear nucleus, the first central auditory structure to receive input from the cochlea, has been shown to be disrupted by ARHL. Fusiform cells (FC), the principal output cell of the dorsal part of the cochlear nucleus (DCN), mature physiologically during hearing onset. Specifically, FCs increase in rate of action potential (AP) rise and decay, stabilizing by postnatal day 14 (P14) in mice. However, whether FC intrinsic electrophysiological properties and morphological characteristics continue to change throughout the life of mice, and how they change due to ARHL, is unknown. We characterized electrophysiological and morphological properties of FCs from CBA/CaJ mice at five stages of age: preweaning (P15-20), pubescent (P21-49), young adult (P50-179), mature adult (P180-364), and old adult (P550-578). Our old adult mice had smaller auditory brainstem evoked response amplitudes and loss of some hair cells, indicative of ARHL onset. We observed no change in FC membrane properties with age. FCs from the old adult group had elevated firing rates, faster repolarization rates, and shorter AP half-widths. Morphologically, there was no change in FC soma shape or size. However, a significant decrease in basal dendritic arborization occurred between preweaning and pubescent ages, followed by an increase in our old adult group, suggesting age-dependent remodeling of the basal dendritic tree at the onset of ARHL. Together, these results suggest that FC physiology and morphology are relatively stable post weaning and become altered during the onset of ARHL.

Forced exercise modulates retinal inflammatory response and regulates miRNA expression to promote retinal neuroprotection during degeneration
Background: Our labs have demonstrated exercise is protective in animal models of retinal degeneration (RD). Inflammation drives RD progression, and is regulated by the recruitment and reactivity of glia cells as well as through small non-coding RNAs, microRNAs (miRNAs). Here, we explore the effects of treadmill exercise on the recruitment and reactivity of retinal inflammatory cells within the neural retina and miRNA expression in a light-induced retinal degeneration model (LIRD) that exhibits phenotypes found in patients with RD. Methods: Male 6-week-old BALB/c mice were randomly assigned to either active or inactive groups. Active groups were exercised by treadmill 1 hour a day for two weeks at a speed of 10m/min, meanwhile inactive groups were placed on static treadmills for the same duration. Light induced retinal degeneration (LIRD) was induced during the second week of exercise using light exposure of 5000 lux, control animals were kept at 50 lux. Retinal function was assessed using electroretinography (ERG) 5 days after LIRD. Retinas were collected 1-day and 5-days post-LIRD, sagittal sections were stained for inflammatory markers (GFAP and Iba1), TUNEL (cell death), and photoreceptor nuclei (outer nuclear layer; ONL) were quantified. RNA was extracted and miRNA expression quantified with GeneChip miRNA 4.0 array. Results: Active+LIRD mice demonstrated significant preservation of retinal function, evidenced by higher a-wave and b-wave amplitudes in ERG 5-days post-LIRD, compared to inactive+LIRD mice. Retinal sections from active+LIRD mice had fewer Iba1+ cells and decreased GFAP labeling 5-days post-LIRD compared to inactive+LIRD mice. Active+LIRD mice had fewer ONL TUNEL+ cells compared to inactive+LIRD mice. Inactive+LIRD mice showed a decline in ONL counts 1-day post-LIRD with significant loss 5-days post-LIRD compared to active+LIRD mice. In active groups, exercise promoted significant differences in miRNA expression, such as miR-302b, miR-192-5p, miR-187 compared to inactive groups. Conclusions: Our results indicate that treadmill exercise preserved photoreceptor density, slowed and or prevented apoptosis in the ONL, and decreased the presence/recruitment of inflammatory cells in the neural retina. Altered miRNA expression profiles in active groups are associated with cell survival (miR-302b), oxidative stress regulation (miR-192-5p) and photoreceptor homeostasis (miR-187). These results reveal how exercise alters the retinal inflammatory response over the course of 1-day to 5-days, providing insight into exercise-based therapies and treatments for RD and neuroinflammatory diseases.

Neural and Behavioural Correlates of Variance of Sensory Evidence
Neurobiology of perceptual decisions has largely focused on the neural correlates of the mean strength of sensory evidence. Much less is known about the neural coding of sensory variability. Here, we analyzed the EEG signals obtained from participants who judged the mean orientation of a sequence of gratings with varying variance but constant mean to identify the neural signatures of sensory variance and their relation to individual differences in choice confidence. The neural responses in the stimulus-entrained (4 Hz) and alpha (9 to11 Hz) bands tracked variability independently of mean. The frontal and centro-parietal regions demonstrated a quadratic relationship (i.e., strongest responses to intermediate levels of uncertainty) to the standard deviation of the sequence. The occipital response coded the visual stimulus variability linearly. These neural markers of variability were correlated with inter-individual differences in computational components of metacognition. Centro-parietal activity was most predictive of metacognitive sensitivity, aligning with its known role in evidence accumulation. These findings advance our understanding of how the brain dynamically encodes uncertainty and help better characterise the electrophysiological basis of individual differences in metacognitive evaluation.

No neurobehavioral evidence for reduced motivational potential of social rewards in alcohol use disorder
The mesolimbic dopamine system plays a central role in motivating behavior. In alcohol use disorder (AUD), this system is thought to be dysfunctional, leading to hyperreactivity to alcohol-related cues. In contrast, evidence on how individuals with AUD respond to alcohol-unrelated reward cues is inconclusive, and the motivation for social rewards has not yet been investigated. To address this gap, 36 individuals with AUD and 34 healthy controls performed an incentive delay task to assess social reward anticipation with a monetary and a non-reward control condition while undergoing functional magnetic resonance imaging. The ventral striatum was defined as region of interest because of its central role in neuronal circuits for motivation. Neither behavioral nor neuroimaging data provided any evidence of altered motivation for social or monetary rewards in AUD. Exploratory whole-brain analyses only revealed stronger activation in the occipital/cuneal cortex in individuals with AUD than in healthy controls across all trials. Together, these results suggest that sensitivity to social reward cues is not fundamentally impaired in AUD. Furthermore, they imply that motivational changes related to the substance do not generally alter the reward potential of alcohol-unrelated domains in AUD, opening perspectives for social-behavioral treatments for this disorder.

Perspective matters: using past experiences to understand others' insensitivity to physical pain.
Prior research has shown that autobiographical memory (AM) supports empathy, allowing individuals to use the self as a model for understanding others. However, when the subjective experience of an event diverges between observer and target, relying on AM may hinder empathic processes, rather than support them. In this study, we recorded electroencephalographic (EEG) data from 36 healthy young adults during a pain decision task to investigate empathy for individuals described as either sensitive to physical pain (like the participants) or clinically insensitive to physical pain. Participants reported lower empathy for insensitive than for sensitive targets, regardless of whether they had personally experienced the specific event that caused physical pain. Event-related potential (ERP) analyses revealed differences in neural responses to sensitive and insensitive targets at a late stage of processing, in the discending phase of the P300 component; these differences were positively correlated with individual differences in empathy. To determine the underlying mechanisms, we applied multivariate pattern analysis (MVPA) to assess whether empathy for physical pain relies on AM reactivation or instead engages active perspective taking. We observed that AM reactivation can serve as a flexible mechanism that supports empathy by enabling observers to shift perspective when direct experiential overlap is lacking.

Network Signatures of Disease Progression and Core Symptoms in Dementia with Lewy Bodies Distinct from Alzheimer's Disease
Background. Resting-state fMRI studies in dementia with Lewy bodies (DLB) and Alzheimer's disease (AD) have described connectivity alterations in large-scale brain networks. However, little is known about functional changes across disease stages, particularly in DLB. Objective. To investigate functional connectivity of key brain networks in DLB patients at different stages, compare them to AD and healthy controls (HC) and examine associations with core clinical symptoms. Methods: Ninety DLB patients, comprising 63 with mild cognitive impairment (MCI-DLB) and 27 with dementia (d-DLB), along with 25 AD patients (11 MCI-AD and 14 d-AD) and 34 HC underwent clinical, neuropsychological and resting-state fMRI assessment. ROI-to-ROI analyses were performed using the CONN toolbox, (pFDR<0.05). Results: The DLB group showed reduced functional connectivity within the salience network (SN) compared with HC, but did not differ from AD. While MCI-DLB patients showed no significant differences, d-DLB patients showed reduced SN and frontoparietal network (FPN) connectivity compared to HC and AD. SN connectivity was associated with severity of fluctuations and FPN connectivity with REM sleep behavior disorder and cognitive decline in DLB. In contrast, in the AD group, decreased default mode network (DMN) connectivity was associated with lower MMSE scores. Conclusion: SN and FPN connectivity impairments relate to disease progression and core clinical features in DLB, whereas DMN connectivity is linked to cognitive decline in AD. These distinct patterns highlight divergent paths of network dysfunction in the two diseases, offering insight into their underlying mechanisms and clinical expression.

Purkinje cell collaterals preferentially target a subtype of molecular layer interneuron
In addition to providing outputs from the cerebellar cortex, Purkinje cell (PC) axon collaterals target other PCs, molecular layer interneurons (MLIs), and Purkinje layer interneurons (PLIs). It was recently shown that MLIs consist of two subtypes, but the properties of PC synapses onto these subtypes was not known and it was assumed that all PC collateral to MLI synapses would provide positive feedback to PCs. Clarifying the PC connectivity onto MLI subtypes is vital to understating the influence of feedback from PC collaterals because MLI1s primarily inhibit PCs whereas MLI2s mainly inhibit MLI1s and disinhibit PCs. Here we use a combination of serial EM and optogenetic studies to characterize PC synapses onto MLI subtypes in mice. EM reconstructions show that PCs make 53% of their synapses onto other PCs, 32% onto PLIs, 6% onto MLI1s and 7% onto MLI2s. Since there are far more MLI1s than MLI2s, each MLI2 is expected to receive many more synapses than each MLI1. In slice experiments, optogenetic activation of PCs evokes inhibitory currents in most MLI2s, but primarily disinhibits MLI1s. We also find that candelabrum cells, a type of PLI, form many more synapses onto MLI1s than MLI2s. It is therefore expected that both PC-MLI2-MLI1-PC and PC-PLI-MLI1-PC pathways allow increased PC firing to disinhibit MLI1s, which are known to reduce dendritic PC calcium signals and suppress plasticity at granule cell to PC synapses. These pathways provide negative feedback that act in concert with PC-PC synapses to counter elevations in PC firing.