bioRxiv Subject Collection: Neuroscience's Journal

Social Exclusion Amplifies Behavioral Responses to Physical Pain via Insular Neuromodulation
The Pain Overlap Theory proposes that the experience of social pain overlaps with and amplifies the experience of physical pain by sharing parts of the same underlying process- ing systems. In humans, the insular cortex has been implicated in this overlap of physical and social pain, but a mechanistic link has not been made. To determine whether social pain can subsequently impact responses to nociceptive stimuli via convergent electrical signals (spikes) or convergent chemical signals (neuromodulators), we designed a novel Social Exclusion paradigm termed the Fear of Missing Out (FOMO) Task which facilitates a mechanistic investigation in mice. We found that socially-excluded mice display more severe responses to physical pain, disrupted valence encoding, and impaired neural representations of nociceptive stimuli. We performed a systematic biosensor panel and found that endocannabinoid and oxytocin signaling in the insular cortex have opposing responses during trials where mice were attending or not attending to the Social Exclusion events respectively, demonstrating distinct neuromodulatory substrates that underpin different states of Social Exclusion. We also found that intra-insular blockade of oxytocin signaling increased the response to physical pain following Social Exclusion. Together these findings suggest Social Exclusion effectively alters physical pain perception using neuromodulatory signaling in the insular cortex.

Acetaminophen attenuates pathological pain through a mechanism that requires CB1 cannabinoid receptors and the enzyme diacylglycerol lipase in mice
Acetaminophen (APAP) is commonly used as a pain and fever reliever, but its mechanisms remain unclear. Conflicting evidence implicates the endocannabinoid system in the effects of APAP. We tested the hypothesis that the analgesic effects of APAP were dependent upon both CB1 cannabinoid receptors and diacylglycerol lipase (DAGL), an enzyme which catalyzes formation of the endocannabinoid 2-arachidonoylglycerol. We examined the impact of APAP, administered in the presence and absence of DAGL inhibitors, on mechanical hypersensitivity in mice using models of inflammatory (induced by intraplantar injection of complete Freunds adjuvant (CFA)) and post-surgical (induced by incisional injury) pain. Pharmacological specificity was assessed using global (Rimonabant, AM251) and peripherally restricted (AM6545) CB1 antagonists. APAP produced a dose-dependent attenuation of inflammation-induced mechanical hypersensitivity, but did not alter peripheral edema in the CFA-injected paw. APAP also attenuated mechanical hypersensitivity in mice with incisional injury. The DAGL inhibitors, RHC-80267 or DO34, attenuated the anti-allodynic effects of APAP in both models of pain. CB1 receptor antagonists (Rimonabant and/or AM251) suppressed the antinociceptive effect of APAP in both pain models. The peripherally-restricted CB1 antagonist AM6545 did not alter the anti-allodynic effects of APAP. We also assessed the impact of APAP on tail-flick antinociception, locomotor behavior, and body temperature. APAP produced hypothermia and hypolocomotion at the highest dose, but these effects were not blocked by RHC-80267 or AM251. APAP did not produce tail flick antinociception. Our studies demonstrate that the analgesic effects of APAP observed in mouse models of pathological pain require both DAGL and CB1 activation. Our findings support a potential mechanism of APAP-induced analgesic action involving the enzyme DAGL and CB1 receptors.

Neuropeptidergic transmission shapes emergent properties of prefrontal cortical circuits underlying learning
The prefrontal cortex (PFC) is essential for top-down control of affect and its dysfunction is implicated in many psychiatric disorders. Inhibitory interneurons expressing somatostatin have been implicated in cognition, affect, and disease. However, somatostatin's function as a neuropeptide transmitter remains unclear. Here, we investigated the contribution of somatostatin neurotransmission in differentiating between salient (rewarding or aversive) and neutral outcomes. Monitoring somatostatin release and somatostatin receptor antagonism revealed time-dependent regulation of outcome-specific associative learning during acquisition. We found that somatostatin transmission enables configural representations incorporating a salient, aversive outcome in prefrontal cortical neurons, and a threat-driven shift in population-level network activity in-vivo. These findings show a novel role for somatostatin, an interneuron 'cellular marker', signaling in shaping learning and emergent network dynamics. Further this framework revealed that reduced somatostatin neuropeptidergic transmission may impair top-down control of affective behaviors observed in mental health disorders, suggesting potential new avenues for therapeutic intervention.

Structured experience shapes strategy learning and neural dynamics in the medial entorhinal cortex
Animals can solve new, complex tasks by reusing and adapting what they've learned before. This kind of flexibility depends not just on having prior experience, but on how that experience was structured in the first place. The design of early training curriculum is especially important: poorly structured experiences can hinder abstraction and limit generalization, while carefully structured training promotes more flexible and adaptive behavior. Yet, the neural mechanisms supporting this process remain unclear. To investigate how early training shapes learning we first trained recurrent neural networks (RNNs) on variants of an odor-timing task previously used to study complex timing behavior in mice. We then tested the RNN predictions on how previous experience affects generalization using behavioral and electrophysiological recordings in mice trained on the same task using staged training sequences. RNNs and mice trained without well-structured early experience developed rigid strategies and made repeated errors. In contrast, those given more balanced early training were better able to generalize and showed similar neural activity patterns that reflected the task's underlying temporal structure. Using dynamical systems approaches, we reveal a mechanism for this effect: networks trained with appropriately structured curricula developed distinct dynamical motifs that support the correct abstractions when complexity was increased. Networks that lacked early training or received remedial curricula developed single fixed-point solutions that failed to generalize beyond the training stimuli. Together, these findings demonstrate that it is not just the presence of prior experience, but its structure, that governs how flexible and generalizable knowledge emerges in both biological systems and computational models.

Alpha power indexes working memory load for durations
Timing, that is estimating, comparing, or remembering how long events last, requires the temporary storage of durations. How durations are stored in working memory is unknown, despite the widely held view of memory systems' central role in timing. Here, we investigated the neural signatures of a sequence of durations (n-item sequence) held in working memory. We recorded human participants using magnetoencephalography (MEG) while they performed an n-item delayed reproduction task, which required to encode a sequence of durations, maintain it, and then reproduce it. The number of items in a sequence (one or three) and the duration of the sequence were orthogonalized. Our results show that during working memory maintenance, the number of durations, not the duration of the sequence, affected recall precision and could be decoded from alpha and beta oscillatory activity. Parieto-occipital alpha power showed a direct link with the precision of temporal reproduction. Our results extend earlier behavioral findings suggesting that durations are itemized in working memory and that their number, not their duration, modulates recall precision (Herbst et al., 2025). Crucially, we establish that alpha power reflects a universal signature of working memory load and mediates recall precision, even for abstract information such as duration.

Diverse activity in prefrontal projections promotes temporal control of action
Prefrontal neurons can have diverse activity during cognitive functions like working memory, attention, and timing; however, the importance of this heterogeneity is unclear. Our goal was to better understand the diversity of prefrontal activity through connectivity. We harnessed circuit-specific tools to capture activity within prefrontal projections during interval timing, an elementary cognitive process that requires working memory for temporal rules and attention to the passage of time to estimate a temporal interval of several seconds. We used human electroencephalography and single neuronal recordings in mice to capture prefrontal activity during interval timing, with major patterns characterized by time-dependent ramping (monotonic changes) over a temporal interval. We then leveraged retrograde viruses to interrogate prefrontal cortex (PFC) projections to the mediodorsal thalamus (PFC-MD) and to the dorsomedial striatum (PFC-DMS). We report three novel results. First, circuit-specific calcium fiber photometry revealed that PFC-MD and PFC-DMS activity encoded distinct temporal signals, with PFC-MD projections ramping down and PFC-DMS ramping up to interval timing response times. Second, circuit-specific inactivation revealed that PFC-DMS inactivation disrupted animals internal estimates of time. Third, circuit-specific single-nucleus RNA sequencing of prefrontal projections revealed distinct transcriptomic profiles between PFC-MD and PFC-DMS projections, with enriched genes for cortical layers and neuromodulators, and specific genes such as Cux2, Camk2n1, Htr4, and Foxp2. These data suggest differences in gene expression and connectivity give rise to the diversity of prefrontal activity during interval timing. These findings advance our fundamental understanding of prefrontal function and dysfunction in human disease.

Spontaneous spiking statistics form unique area-specific fingerprints and reflect the hierarchy of cerebral cortex
The cerebral cortex, from sensory to higher cognitive areas, is hierarchically organised Several dynamical and anatomical measures, such as timescales and neurotransmitter receptor expression, have independently been linked to the cortical hierarchy. However, a systematic quantitative link between anatomical markers of the cortical hierarchy and single-neuron dynamics has not yet been established. Here, we hypothesise that the single-neuron spontaneous spiking statistics uniquely characterise each cortical area, and that they quantitatively correlate with the cortical hierarchy. We consider the spontaneous activity of neurons in seven cortical areas (V1, V4, DP, 7A, M1, PMd, PFC) in macaques in the eyes-open and eyes-closed conditions. First, we show that the firing rate, inter-spike interval variation, and cross-correlation form a unique fingerprint of the cortical areas, but only when considering them in combination. Second, we find that the differences between the spiking statistics strongly correlate with multiple anatomical markers of the cortical hierarchy, especially in the eyes-closed condition. We also observe a correlation between autocorrelation timescales and the anatomical hierarchy, consistent with previous findings. In conclusion, we demonstrate that spontaneous single-neuron spiking activity reflects the hierarchical organisation of the cerebral cortex: distinct spiking statistics for hierarchically distant areas; similar statistics for nearby areas. Our results thus add a new dynamical dimension to the concept of the cortical hierarchy.

Opposing Modulation of EEG Aperiodic Component by Ketamine and Thiopental: Implications for the Noninvasive Assessment of Cortical E/I Balance in Humans
The balance between excitatory and inhibitory (E/I) activity is critical for brain function, and its disruption is implicated in neuropsychiatric disorders. Electrophysiological signals can be decomposed into periodic (oscillatory) and aperiodic components. In the power spectrum, the periodic component appears as narrowband peaks, while the aperiodic component underlies its characteristic 1/f power-law decay. Computational models predict that shifts in E/I balance alter the exponent in specific directions. In a randomized, double-blind, placebo-controlled, within-subject study, healthy volunteers received subanesthetic doses of ketamine and thiopental during an EEG oddball task. These drugs have opposite effects on E/I balance but comparable sedative profiles. Ketamine reduced the PSD exponent, while thiopental increased it, consistent with computational predictions. Changes in the exponent were associated with subjective and cognitive effects. These findings suggest that the PSD exponent has potential as a noninvasive EEG biomarker sensitive to transient shifts in cortical E/I balance.

Cerebral plasticity after hypoglosso-facial anastomosis in facial palsy: a magnetoencephalography study
Background: Hypoglosso-facial anastomosis (HFA) consists in suturing the proximal part of the hypoglossal nerve with the distal part of the facial nerve in patients with facial palsy. Axonal regrowth through the anastomosis makes it possible to restore facial motor skills, which become spontaneous after physiotherapy. This suggests cerebral plasticity. Objective: We used magnetoencephalography (MEG) in a pilot study to test this hypothesis. Methods: Twenty-one healthy volunteers (CTRL) and 12 patients after HFA performed 5 motor tasks with MEG and electromyographic recordings: eyelid closure, smile, tongue protraction, mastication and thumb flexion. For each task, we picked the location of the maximum source activity within the precentral gyrus. We calculated the distances between this location and the vertex for each task and a somatotopy index. Results: There was an interaction between the participant group and the task (F(4,124)=4.07, p=0.0039). In CTRL, the maximum source location was statistically different between smile and tongue tasks and between eyelid and tongue tasks (p<0.001). No such difference was observed in HFA (p=1.000). 90.5% of CTRL and 41.7% of HFA showed a normal somatotopy (p=0.0046). Conclusions: In CTRL, the organization of the cortical motor areas was similar to that of Penfield motor Homunculus. In contrast, in HFA, eyelid closure, tongue protraction and smile areas were not significantly distinct. This supports the hypothesis of cerebral plasticity after HFA. The Ethical Committee of Paris Idf VI approved the study (CPP Ouest 6-CPP975-HPS2

Neuro-Metabolic and Vascular Dysfunction as an Early Diagnostic for Alzheimer's Disease and Related Dementias.
Background Alzheimer's disease (AD), the most common neurodegenerative condition, is characterized by significant cognitive decline. To detect these changes, diagnostic imaging approaches rely primarily on single modalities to identify structural and functional changes, thus hindering patient stratification and treatment effectiveness. Recent studies suggest the brain undergoes anatomical and functional restructuring, resulting in neuro-metabolic and vascular dysregulation (MVD) prior amyloid-{beta}; accumulation. Several lines of evidence suggest that MVD begins at an early age and leads to the onset of AD. Therefore, we hypothesized that detecting MVD may serve as a sensitive and early noninvasive diagnostic tool, and was assessed in a retrospective clinical population from CN to AD. Methods A total of 403 subjects with 18F-FDG PET (FDG), and ASL MRI scanned within 180 days from ADNI 2 and 3 were included, where: CN/EMCI/MCI/LMCI/AD(95/71/112/42/83), M/F(55/45%). CBF images were generated from ASL images using ExploreASL. CBF and FDG images were used to evaluate cerebral perfusion and metabolism, respectively, and were registered to the MNI152+ atlas. Mean intensities across 59 brain regions were ratioed with whole brain mean values. z-scores were computed for disease subjects relative to a reference and projected onto a Cartesian space. Results were aligned with transcriptomic signatures and clinical cognitive assessments. Findings Our findings suggest that disease progression follows a stage-dependent MVD pattern that can identify at-risk brain regions. Although each region progresses at a different pace, regions related to memory, cognitive tasks, and motor function showed significant early dysregulation. Importantly, these changes aligned with transcriptomic and cognitive signatures. Interpretation We identified an MVD pattern that at-risk brain regions follow across the AD spectrum. In addition, our study shows that MVD in brain regions varies by sex and disease stage, making it a sensitive tool for early AD diagnosis. Moreover, this could improve patient monitoring, stratification, and therapeutic testing.

FLP-15 modulates the amplitude of body bends during locomotion in Caenorhabditis elegans
Locomotion is essential for executing most behaviours. In Caenorhabditis elegans. Efficient locomotion is exhibited as a result of the coordination of excitatory and inhibitory signals from the nervous system onto the body-wall muscles. Although neurotransmitters play a vital role in maintaining and executing coordinated movements, neuropeptides have emerged as important players in the regulation and sustenance of locomotory states. In our previous study we explored the role of the neuropeptide FLP-15 in regulating reversal frequency during foraging behaviour in C. elegans. We were also interested in exploring other possible locomotory defects in flp-15 mutant animals. In this work we show that flp-15 mutants show an increased length of reversals during foraging resulting in defects in maintaining the direction of reversals. Mutants in flp-15 exhibited a floral pattern of reversals as opposed to near linear patterns of reversal in wild-type control animals. We further show that the defect in maintaining the direction of reversals could be due to increased amplitude of the body-bends with flp-15 mutants showing a large increase in the mean amplitude of body-bends. Our data suggests that FLP-15 partially functions through the G-protein coupled receptor (GPCR), NPR-3, to regulates the amplitude of body-bends. Finally, we show that loss of flp-15 leads to an increase in the expression of another neuropeptide, NLP-12, whose over expression has been implicated in causing increased amplitude of body-bends allowing us to speculate that the regulation of NLP-12 by FLP-15 may allow for the observed locomotory defects in flp-15 mutant animals.

Elusive scent of fear: no evidence of olfactory reversal conditioning in humans
Reversal learning offers a window into how associations are acquired, updated, and overwritten. Because olfactory inputs bypass much of the thalamus and are tightly linked to emotion, we examined whether humans can flexibly form and subsequently reverse aversive associations to smells. Thirty healthy adults underwent an olfactory reversal conditioning protocol in which one neutral odor (CS+) was followed by a 90 dB aversive sound (US) and a second odor (CS-) was not. After five blocks the contingencies were reversed. Throughout 300 trials we collected ratings of pleasantness and intensity together with autonomic physiological indices (skin conductance, ECG, photoplethysmography, respiration), facial EMG, and 64-channel EEG. Contrary to expectations, pleasantness, intensity, and all autonomic or facial muscle measures failed to differentiate CS+ and CS- either before or after reversal (all p > .01). Event-related potentials, alpha suppression, heart rate and pulse wave responses likewise showed no CS specificity. Only multivariate classifiers: trained (i) on the time-domain EEG signal and (ii) on alpha-band activity, separately, distinguished CS+ from CS- at above-chance levels in late post-stimulus intervals. These neural signatures did not translate into overt physiological or behavioural differences. The pattern suggests that, at least with neutral odors and an auditory US, olfactory fear learning is subtle, spatially variable across the cortex, and easily masked in group-level averages. Our findings highlight both the promise of multivariate EEG for detecting fragile olfactory associations and the challenge of eliciting robust conditioned responses with cross-modal (odor-sound) pairings.

Eccentric cycling improves motor learning more than concentric cycling
An acute bout of aerobic exercise (AAE) performed before practicing a motor task can enhance skill acquisition and motor learning. To date, research on the effects of AAE on motor learning has focused exclusively on concentric cycling, leaving the impact of eccentric cycling unexplored. Unlike concentric cycling, eccentric cycling involves muscle lengthening while resisting the reverse movement of the pedals and is characterized by greater force production with lower cardiovascular and metabolic cost. Regarding neuroplasticity changes, eccentric contractions induced a prolonged decrease in intracortical inhibition compared to concentric contractions. Eccentric cycling AAE also increases activation in cognitive-related regions. Given the involvement of these regions and motor cortex excitability in motor learning, we hypothesized that eccentric cycling AAE would enhance motor learning to a greater extent than concentric AAE. A total of 60 young healthy individuals were allocated to one of three groups that performed 20 min of: i) eccentric cycling; ii) concentric cycling; or iii) seated rest. Both cycling AAE conditions were performed at a power equivalent to 70% peak heart rate (i.e., moderate intensity). A continuous tracking task was used to assess motor skill acquisition (immediately after the intervention) and motor learning (48 h retention test). For both acquisition and retention, the eccentric group outperformed both the concentric and rest groups, while the concentric group also showed a better performance compared to the rest group at retention. Thus, we demonstrated that eccentric cycling AAE enhances motor learning to a greater extent than concentric cycling AAE, while also confirming previous work that showed enhanced motor learning following concentric cycling AAE compared to rest. Our findings suggest that eccentric cycling AAE may have important implications for exercise protocols prescribed in sports-related and clinical contexts.

Reduced triacylglycerols and lipid droplets are associated with resilience to Alzheimers disease
Introduction While it has become clear that alterations in lipid metabolism are associated with AD, it is unclear how they contribute to both cognitive decline and the pathophysiology of AD. Methods We performed lipidomics and activity-based protein profiling in the frontal cortex of control, AD and resilient donors, i.e. individuals with AD pathology without cognitive decline. Subsequently we integrated these data using multi-omics factor analysis and correlated the multi-omics profiles to disease and clinical parameters. Results The most pronounced alterations in lipids were in the {omega}6-derived oxylipins, which were particularly increased in the AD patients. Both triacylglycerols (TAGs) and lipid droplets were more abundant in the AD donors compared to the resilient donors. Enzyme activities showed a similar direction in the AD and resilient donors, including decreased activity of ABHD6. Multi-omics factor analysis showed that increased oxylipins, loss of inhibitory cells, synaptic genes and genes related to the inflammatory response were associated with A{beta} plaque load in both AD and resilient donors. Conclusion Our multi-omics data show a response associated with A{beta} load shared among AD and resilient donors and, for the first time, reduced lipid droplets in resilient donors.

Normative Brain Entropy Across the Lifespan
Brain entropy (BEN), a measure of the complexity and irregularity of neural has emerged as a promising marker for cognitive and clinical traits. However, normative lifespan trajectories of BEN remain underexplored. In this study, we investigated age-related changes in BEN across the human lifespan using Sample Entropy (SampEn). BEN was estimated from resting-state fMRI data collected from multiple Human Connectome Project cohorts (N = 2,415, ages 8-89 years), and normative growth curves were modeled using the GAMLSS framework. Results revealed a nonlinear increase in average BEN from childhood to older adulthood, with females exhibiting significantly higher BEN than males. Regional and network-level analyses confirmed similar age-related patterns.

Unbiased genetics identifies a glutamatergic signaling network as a mediator of daily sleep patterns.
Sleep is a fundamental, conserved behavior important for survival. In many species, sleep behavior is controlled by poorly understood interactions between a system of circadian rhythms (CR), which promote sleep at ecologically appropriate times, and a homeostatic sleep drive that accumulates with time awake. The CR is a cellular phenomenon, driven by molecular oscillations of clock genes in nearly all cells. Emerging evidence indicates neuronal synapses are a key locus for the accumulation and resolution of sleep need, supporting a cellular basis of sleep need. Indeed, efforts to understand the genetic basis of sleep need identified Homer1a, a regulator of synapse homeostasis. To develop further insight into the genetic basis of sleep regulation, we measured daily sleep patterns in genetically diverse strains of mice from the Collaborative Cross. Strains with 1) highly consolidated light-phase sleep, or 2) fragmented, arrhythmic sleep, were identified for genetic analysis using quantitative trait loci (QTL) mapping. Excitingly, in F2 hybrids, 19 of 32 metrics of sleep and circadian behavior mapped to a narrow QTL containing GRM5, a postsynaptic glutamate receptor and binding partner of Homer1a, and GCPII, an astrocytic enzyme that regulates NAAG, a peptide agonist for the presynaptic/astrocytic glutamate receptor GRM3. Collectively, these genes form a coordinated glutamatergic signaling network across the tri-partite synapse. Pharmacology targeting GRM5, GCPII, and GRM3 strongly modulated sleep, functionally validating them as sleep-regulating genes. Our findings support a model in which synapses act as a cellular site for integration of circadian and sleep-need signals to regulate daily sleep patterns.

Sex-dependent effects of peptidylarginine deiminases on neutrophil function and long-term outcomes after spinal cord injury
Traumatic spinal cord injury (SCI) initiates an influx of peripheral immune cells to the spinal cord parenchyma that compound tissue damage and restrict functional recovery. Neutrophils infiltrate the spinal cord within the first day after injury, releasing extracellular traps (NETs) comprised of decondensed DNA, modified histones, and granule enzymes, that can worsen tissue damage. Peptidylarginine demininases (PADs), particularly PAD4, have been indicated as mediators of NET formation by facilitating the decondensation of nuclear chromatin via histone citrullination. Though PADs have been shown to be regulated by sex hormones, sex-differences in PAD regulation of neutrophil function in the context of CNS injury have yet to be explored. In this work, we investigated the role of PADs in recovery after SCI using Cl-amidine, a pan-PAD inhibitor. Strikingly, Cl-amidine treated mice exhibited sex-dependent changes to motor function, body weight, and white matter sparing after SCI. Acutely, Cl-amidine treated mice had reduced NET accumulation in the blood and decreased spinal cord neutrophil granularity. Analysis of publicly available scRNA-seq data revealed that female bone marrow neutrophils exhibited elevated Padi4 expression relative to their male counterparts. We then utilized Padi4 knockout (Padi4-/-) mice to assess the role of PAD4 in long-term recovery of male and female mice after SCI. While we observed no changes in motor recovery, a sex-dependent effect on tissue sparing was observed with Padi4 deficiency. These data are the first description of sex differences in PAD-mediated neutrophil function after SCI and highlight the importance of inclusion of both sexes in pre-clinical research.

Molecular pathology of acute spinal cord injury in middle-aged mice
The median age of sustaining a spinal cord injury has steadily increased from 29 to 43 over the last several decades. Although more pre-clinical studies in aged rodents are being done to address this shift in demographics, there have not been comprehensive transcriptomic studies investigating SCI pathobiology in middle-aged mice. To address this gap in knowledge, we compared behavioral, histopathological, and transcriptional outcomes in young (2-4 months-old) and middle-aged (10-12 months-old) mice. In contrast to previous studies, open field tests showed no differences in locomotor recovery between the young and middle-aged mice over a one-month period. The injury site also demonstrated similar histopathology in terms of lesion size, and numbers of macrophages and fibroblasts. Acutely after injury, proliferation of macrophages, fibroblasts, and astrocytes were also similar between the two age groups. In addition, spatial transcriptomics showed similar transcriptionally defined regions around the injury site at 3 days post injury. However, single cell RNA-sequencing of the cells at the injury site and surrounding spared tissue showed differences in select cell subpopulations. Taken together, our results indicate that although young and middle-aged mice display similar locomotor recovery and histopathology after SCI, changes in cell subpopulations may underly a decline in repair mechanisms that are manifested after this age.

Low-Intensity Ultrasound Stimulates TAZ in Schwann cells
Mechanosensation, the ability of cells to detect and respond to mechanical forces by transducing them into biochemical signals, is essential for various cellular processes, including morphogenesis, development, tissue homeostasis, and response to injury. In the peripheral nervous system (PNS), Schwann cells play a critical role in nerve development, myelination, and regeneration. These cells are highly responsive to mechanical cues such as tension, compression, and shear forces, which influence their fate, proliferation, differentiation, and regenerative capacity. In this study, we demonstrate that in vitro application of Low Intensity Ultrasound (LIU) transiently increases Schwann cell proliferation. Notably, our results show that LIU selectively activates TAZ, but not YAP, both nuclear transducers of the Hippo pathway. Additionally, we show that the LIU treatment upregulates nerve growth factor (NGF) expression in both Schwann cells and sensory neurons, suggesting a role for LIU in promoting neurotrophic support. This study highlights LIU as a mechanotherapeutic tool that enhances intrinsic regenerative functions in Schwann cells, such as neurotrophic support to neurons via NGF.

From cognition to compensation: Neurocomputational mechanisms of guilt-driven and shame-driven altruistic behavior
Guilt and shame are key moral emotions that influence mental health and regulate social behavior. Although prior research has examined the psychological and neural correlates of these emotions, the cognitive antecedents trigger them, as well as their transformation into social behavior, remain insufficiently understood. In this study, we developed a novel task to investigate how two crucial cognitive antecedents, harm and responsibility, elicit guilt and shame, and how these emotions subsequently drive compensatory behavior, by combining functional magnetic resonance imaging (fMRI) with computational modeling. Behaviorally, we found that harm had a stronger impact on guilt than on shame, whereas responsibility had a stronger impact on shame than guilt, which support the functionalist theory of emotion. Moreover, compared to shame, guilt exerted a greater effect on compensation. Computational modeling results indicated that individuals integrate harm and responsibility in the form of a quotient, aligning with the phenomenon of responsibility diffusion. The fMRI results revealed that brain regions associated with inequity represenation (posterior insula) and value computation (striatum) encode this integrated measure. Furthermore, individual differences in responsibility-driven shame sensitivity were associated with activity in theory-of-mind regions (temporoparietal junction and superior temporal sulcus). Guilt- and shame-driven compensatory behavior recruited distinct neural substrates, with shame-driven compensatory sensitivity being more strongly linked to activity in the lateral prefrontal cortex, a region implicated in cognitive control. Our findings provide computational, algorithmic, and neural accounts of guilt and shame.

Evaluation of hippocampal DLGAP2 overexpression on cognition, synaptic function, and dendritic spine structure in a translationally relevant AD mouse model
INTRODUCTION Developing effective therapeutics for Alzheimer's Disease (AD) requires a better understanding of the molecular drivers of the disease. Our previous work nominated DLGAP2 as a modifier of age-related cognitive decline and risk for AD. We tested the hypothesis that overexpression of DLGAP2 in the hippocampus would protect against cognitive and synaptic deficits in a susceptible F1 5XFAD model. METHODS DLGAP2 was overexpressed in the hippocampus of F1 hybrid 5XFAD and nontransgenic littermates using a viral approach. Cognitive function, electrophysiological properties, and dendritic spine morphology were assessed at 6 and 14 months of age. RESULTS DLGAP2 overexpression impaired synaptic plasticity and exacerbated AD-related memory deficits but had minimal effect on spine structure or intrinsic neuronal properties. DISCUSSION We highlight the complex role of DLGAP2 in AD pathology. Targeted interventions involving postsynaptic proteins must consider potential adverse effects on synaptic integrity and cognitive performance, particularly in the context of AD.

Perisynaptic astroglial response to in vivo long-term potentiation and concurrent long-term depression in the hippocampal dentate gyrus.
Perisynaptic astroglia provide critical molecular and structural support to regulate synaptic transmission and plasticity in the nanodomain of the axon-spine interface. Three-dimensional reconstruction from serial section electron microscopy (3DEM) was used to investigate relationships between perisynaptic astroglia and dendritic spine synapses undergoing plasticity in the hippocampus of awake adult male rats. Delta-burst stimulation (DBS) of the medial perforant pathway induced long-term potentiation (LTP) in the middle molecular layer and concurrent long-term depression (cLTD) in the outer molecular layer of the dentate gyrus. The contralateral hippocampus received baseline stimulation as a within-animal control. Brains were obtained 30 minutes or 2 hours after DBS onset. An automated 3DEM pipeline was developed to enable unbiased quantification of astroglial coverage at the perimeter of the axon-spine interface. Under all conditions, >85% of synapses had perisynaptic astroglia processes within 120 nm of some portion of the perimeter. LTP broadened the distribution of spine sizes while reducing the presence and proximity of perisynaptic astroglia near the axon-spine interface of large spines. In contrast, cLTD transiently reduced the length of the axon-spine interface perimeter without substantially altering astroglial apposition. The postsynaptic density was discovered to be displaced from the center of the axon-spine interface, with this offset increasing during LTP and decreasing during cLTD. Astroglial access to the postsynaptic density was diminished during LTP and enhanced during cLTD, in parallel with changes in spine size. Thus, access of perisynaptic astroglia to synapses is dynamically modulated during LTP and cLTD alongside synaptic remodeling.

Lifespan Trajectories of Alpha Rhythm: Dynamic Shifts in Neural Excitation-Inhibition Balance
Alpha rhythm (8-13 Hz), a key neural oscillation in the brain, plays a significant role in cognitive functions and reflects the brain's excitatory-inhibitory (E-I) balance. This study investigates the dynamics of alpha rhythm across the lifespan, focusing on how E-I balance modulates alpha power and peak frequency, and exploring the distinct age-related and sex-specific patterns of alpha activity. Using a computational E-I model, we simulated the impact of different neuronal connections and E-I ratios on alpha rhythm characteristics. The results suggest that self-regulation primarily affects alpha power, while interaction between excitatory and inhibitory neurons influences both alpha frequency and power. We applied this model to real EEG data from 3265 participants across a wide age range, revealing that alpha power and peak frequency exhibit an inverted U-shape across the lifespan, peaking in early adulthood and declining in old age. Significant sex differences in alpha activity were observed primarily during puberty and later in life. Decomposition of the alpha band into periodic and aperiodic components showed that periodic activity follows the inverted U-shape, while aperiodic activity declines exponentially with age. Our findings indicate that alpha rhythm is governed by complex E-I dynamics, with distinct contributions from periodic and non-periodic components, and highlight the role of alpha rhythm in age-related cognitive changes and sex differences in brain function.

Genetic disruption of leucine rich repeat transmembrane protein 4 like 1 induces a pro-social behavioural phenotype in zebrafish
Background: Social behaviour encompasses the wide range of interactions that occur between members of the same species. In humans, disruptions in social behaviour are characteristic of many neuropsychiatric disorders, where both genetic risk factors and synaptic dysfunctions can contribute to the phenotype. Among the genes implicated in synaptic regulation, the synaptic adhesion protein leucine-rich repeat transmembrane protein 4 (LRRTM4) has been identified as a key player in maintaining synaptic function and neuronal circuit integrity. Despite its established role in the nervous system, the potential involvement of LRRTM4 in modulating social behaviour and its contribution to social deficits has yet to be explored. Methods: In the current study, we used zebrafish to study how genetic deletion of lrrtm4l1, a zebrafish orthologue of LRRTM4, affects sociality. For this, the social behaviour of homozygous lrrtm4l1 knockout (KO) zebrafish was analysed in multiple behavioural assays and the brain transcriptome of mutant animals was investigated by RNAseq. Results: KO zebrafish displayed a pro-social phenotype in multiple behavioural assays. Groups of lrrtm4l1 KO zebrafish formed more cohesive shoals and KO individuals spent more time in the vicinity of conspecifics during a social interaction test. They were also less aggressive and in contrast to wild-type zebrafish did not differentiate in their interactions with known and unknown groups of fish. Neurotranscriptomic analysis revealed 560 differentially expressed genes including changes in glutamatergic neurotransmitter signalling, tryptophan-kynurenine metabolism and synaptic plasticity. Conclusion: These findings suggest that lrrtm4l1 is an important regulator of social behaviour in zebrafish. In a translational perspective, LRRTM4 is a promising potential therapeutic target that warrants further investigation in the framework of neuropsychiatric conditions characterized by major social impairments.

Cell-type-specific encoding of prediction and reward in cortical microcircuits during novelty detection
Cortical circuits comprise diverse neuron types whose distinct activity patterns suggest specialized computational roles. Understanding how interneuron subtypes contribute to prediction and novelty detection is key to grounding theories like predictive coding in biological circuitry. We present a cortical microcircuit model that integrates energy-efficient predictive coding and reinforcement learning to explain novelty responses during a visual change detection task. By assigning algorithmic roles to specific interneuron populations, the model reproduces experimentally observed effects in excitatory neurons and in VIP and SST inhibitory subtypes, while offering a theory of how cell-type-specific computations implement predictive coding. Ablation analyses reveal a role for the canonical VIP-SST disinhibitory motif in balancing energy efficiency and representational capacity. We further show that adaptation and Hebbian learning explain contextual--but not absolute or omission--novelty effects, highlighting the importance of integrating these mechanistic models with our normative approach. Together, these findings provide a biologically plausible framework for understanding novelty encoding in cortical circuits.

Independent Generation of Amyloid-β via Novel APP Transcripts
The amyloid precursor protein (APP) is processed by multiple enzymes to generate biologically active peptides, including amyloid-{beta} (A{beta}), which aggregates to form the hallmark pathology of Alzheimers disease (AD). A{beta} is produced through an initial {beta}-secretase cleavage of APP, generating a 99-amino acid C-terminal fragment (APP-C99). Subsequent cleavage of APP-C99 by {gamma}-secretase produces A{beta} peptides of varying lengths. To better understand the transcriptional regulation of A{beta} production, we employed long-read RNA sequencing and identified previously unannotated transcripts encoding APP-C99 with an additional methionine residue (APP-C100), generated independently of {beta}-secretase cleavage. These transcripts are expressed separately from full-length APP, and we observed that cells lacking full-length APP can still produce A{beta} through these shorter isoforms. Importantly, mass spectrometry analysis of cerebrospinal fluid (CSF) revealed peptides consistent with the methionine-extended A{beta} species, supporting the in vivo translation of these transcripts. Our findings reveal an alternative pathway for A{beta} generation and aggregation, highlighting a potential new target for modulating A{beta} accumulation in AD.

Information theoretic measures of neural and behavioural coupling predict representational drift
In many parts of the brain, population tuning to stimuli and behaviour gradually changes over the course of days to weeks in a phenomenon known as representational drift. The tuning stability of individual cells varies over the population, and it remains unclear what drives this heterogeneity. We investigate how a neurons tuning stability relates to its shared variability with other neurons in the population using two published datasets from posterior parietal cortex and visual cortex. We quantified the contribution of pairwise interactions to behaviour or stimulus encoding by partial information decomposition, which breaks down the mutual information between the pairwise neural activity and the external variable into components uniquely provided by each neuron and by their interactions. Information shared by the two neurons is termed redundant and information requiring knowledge of the state of both neurons is termed synergistic. We found that a neurons tuning stability is positively correlated with the strength of its average pairwise redundancy with the population, and that these high-redundancy neurons also tend to show high average pairwise synergy. We hypothesize that subpopulations of neurons show greater stability because they are tuned to salient features common across multiple tasks. Regardless of the mechanistic implications of our work, the stability-redundancy relationship may support improved longitudinal neural decoding in technology that has to track population dynamics over time, such as brain-machine interfaces.

Predicting Neural Activity from Connectome Embedding Spaces
Describing the relationship between activity and connectivity in neural circuits is fundamental to understanding brain function. The connectome of cortical networks is high-dimensional, whereas neuronal activity is often low-dimensional relative to the number of neurons. Consequently, only a small fraction of the information contained in the connectome is relevant to activity. Can this relevant information be identified? In this study, we propose that the activity of each excitatory neuron in the sensory cortex can be approximated as a point in an embedding space defined by its connectome. Using the MICrONS dataset, which provides millimeter-scale, nanometer-resolution data on proofread and coregistered neurons, we perform a correlation analysis and identify a statistically significant alignment between morphological and functional similarities. Topological analysis reveals that the structured representation spaces of both neuronal activity and connectome share a low-dimensional, hyperbolic geometry with exponential scalability. Based on these findings, we develop a simple linear model to reconstruct in vivo neuronal activity by embedding anatomical affinities using multidimensional scaling (MDS). This approach achieves an explanation ratio of $68%$ compared to directly using activity similarity, outperforming the $56%$ obtained using the full connectome. Our results highlight a clear and robust structure-function coupling: although geometry-compatible dimensionality reduction methods discard much of the connectome's detailed information, they prove more effective in predicting neuronal activity, suggesting that synaptic connections may encode an abstract low-dimensional organization.

Delayed forebrain excitatory and inhibitory neurogenesis inSTRADA-related megalencephaly via mTOR hyperactivity
Biallelic pathogenic variants in STRADA, an upstream regulator of the mechanistic target of rapamycin (mTOR) pathway, result in megalencephaly, drug-resistant epilepsy, and severe intellectual disability. This study explores how mTOR pathway hyperactivity alters cell fate specification in dorsal and ventral forebrain development using STRADA knock-out human stem cell derived brain organoids. In both dorsal and ventral forebrain STRADA knock-out organoids, neurogenesis is delayed, with a predilection for progenitor renewal and proliferation and an increase in outer radial glia. Ventrally, interneuron subtypes shift to an increase in neuropeptide-Y expressing cells. Inhibition of the mTOR pathway with rapamycin results in rescue for most phenotypes. When mTOR pathway variants are present in all cells of the developing brain, overproduction of interneurons and altered interneuron cell fate may underlie mechanisms of megalencephaly, epilepsy, and cognitive impairment. Our findings suggest mTOR inhibition during fetal brain development as a potential therapeutic strategy in STRADA deficiency.

Introducing PIGMO, a novel PIGmented MOuse model of Parkinson's disease (V1)
There is a pressing need for the development, characterization, and standardization of anmal models of Parkinson's disease (PD) that properly mimic the cardinal features of this disorder, comprising both the motor phenotype and neuropathological signatures. In the past few years, animal modeling has moved from neurotoxin-based approaches toward viral vectors carrying a given genetic payload of interest. Here, to induce pigmentation of the mouse brain upon systemic delivery, we took advantage of a modified adeno-associated viral vector capsid engineered to bypass the blood-brain barrier and coding for the human tyrosinase gene (AAV9-P31-hTyr). Obtained results revealed an ongoing pigmentation of catecholaminergic centers related to the pathophysiology of PD, such as the substantia nigra pars compacta, ventral tegmental area and locus coeruleus. Moreover, pigmented dopaminergic neurons exhibited Lewy body-like intracytoplasmic inclusions, a progressive nigrostriatal degeneration, and a time-dependent motor phenotype. The bilateral pigmented mouse model of PD generated this way is highly reproducible, does not require stereotaxic surgery for viral vector deliveries, and opens unprecedented possibilities for preclinical testing of therapeutic candidates designed to reduce disease progression rates.

Evaluating ultrastructural preservation quality in banked brain tissue
The ultrastructural analysis of postmortem brain tissue can provide important insights into cellular architecture and disease-related changes. For example, connectomics studies offer a powerful emerging approach for understanding neural circuit organization. However, electron microscopy (EM) data is difficult to interpret when the preservation quality is imperfect, which is common in brain banking and may render it unsuitable for certain research applications. One common issue is that EM images of postmortem brain tissue can have an expansion of regions that appear to be made up of extracellular space and/or degraded cellular material, which we call ambiguous interstitial zones. In this study, we report a method to assess whether EM images have ambiguous interstitial zone artifacts in a cohort of 10 postmortem brains with samples from each of the cortex and thalamus. Next, in matched samples from the contralateral hemisphere of the same brains, we evaluate the structural preservation quality of light microscopy images, including immunostaining for cytoskeletal proteins. Through this analysis, we show that on light microscopy, cell membrane morphology can be largely maintained, and neurite trajectory visualized over micrometer distances, even in specimens for which there are ambiguous interstitial zone artifacts on EM. Taken together, our analysis may assist in maximizing the usefulness of donated brain tissue by informing tissue selection and preparation protocols for various research goals.