bioRxiv Subject Collection: Neuroscience's Journal

Promoting social connectedness through multi-person neurofeedback
Humans are inherently driven to build meaningful relationships, but attempts to socially connect with others are not always successful. This study investigates whether social connectedness can be improved by intentionally regulating inter-brain coupling, a neural correlate of successful social interactions. Using a multi-person neurofeedback system (i.e., a multi-brain computer interface), we showed dyads real-time visualizations of the extent to which their brainwaves (EEG signals) were "in sync". Our results showed that, compared to a sham control group, dyads who received multi-brain neurofeedback exhibited an increase in inter-brain coupling, and, critically, that this increase was associated with a higher sense of social connectedness. A chain mediation analysis suggested that this experience of enhanced social connectedness may have been driven by a sense of joint control and shared intentionality. Together, our findings showcase the potential for regulating inter-brain coupling to optimize human social relationships and behaviors.

Stress-Induced Alteration of Small Extracellular Vesicles Drives Amyloid-Beta Sequestration and Exacerbates Alzheimer's Disease Pathogenesis
While small extracellular vesicles (sEVs) are implicated in amyloid-beta (A {beta}) trafficking, the mechanisms governing their interaction with A {beta} ; aggregates and plaque formation remain unresolved. Here, we report a paradigm-shifting discovery: sEVs undergo dynamic structural remodelling in response to stress, enabling selective binding to A {beta} ; aggregates- a phenomenon absent under normal physiological conditions. Using multimodal stressors, including mechanical (ultrasonication/agitation), physical (hyperthermia), and biological (oxidative damage), we demonstrate that stress-modified sEVs exhibit high-affinity binding to small A {beta} ; aggregates (SA) through scaffold reorganization, as validated by super-resolution microscopy and quantitative colocalization assays. Crucially, these remodelled sEVs act as potent carriers, enhancing SA internalization by neuronal cells in vitro. Strikingly, in post-mortem Alzheimer' s disease (AD) brains and APP-PS1 transgenic mice, sEVs were spatially enriched at amyloid plaque margins, suggesting a direct role in A {beta} ; sequestration and plaque expansion. Consistent with clinical relevance, sEVs isolated from AD patients exhibited an intrinsic SA-binding capacity, recapitulating stress-induced interactions observed experimentally. Our findings reveal that stress-primed sEVs function as pathological chaperones, binding to and internalizing A {beta} ; aggregates, thereby accelerating plaque nucleation and disease progression. This study provides the first evidence of stress-mediated sEV plasticity as a critical driver of A {beta} ; pathology, redefining therapeutic strategies targeting extracellular vesicle biology in neurodegenerative disorders.

Correlations of neural predictability and information transfer in cortex and their relation to predictive coding
Predictive-coding like theories agree in describing top-down communication through the cortical hierarchy as a transmission of predictions generated by internal models of the inputs. With respect to the bottom-up connections, however, these theories differ in the neural processing strategies suggested for updating the internal model. Some theories suggest a coding strategy where unpredictable inputs, i.e., those not captured by the internal model, are passed on through the cortical hierarchy, whereas others claim that the predictable part of the inputs is passed on. Here, we addressed which neural coding strategy is employed in cortico-cortical connections using an information-theoretic approach. Our framework allows for quantifying two core aspects of both strategies, namely, predictability of inputs and information transfer, through local active information storage and local transfer entropy, respectively. A previous study on the neural processing of retinal ganglion cells connected to the lateral geniculate nucleus showed a coding for predictable information, captured by an increase in the information transfer with the predictability of inputs. Here, we further investigate predictive coding strategies at the cortical level. In particular, we analyzed LFP activity obtained from intracranial EEG recordings in humans and spike recordings from mouse cortex. We detected cortico-cortical connections with increasing information transfer with the predictability of inputs in recorded channels from frontal, parietal and temporal areas in human cortex. In the mouse visual system, we detected connections exhibiting both an increase and decrease in the information transfer with input predictability, although the former was predominant. Our evidence supports the presence of both predictive coding strategies at the cortical level, with a potential predominance of encoding for predictable information.

NeuroConText: Contrastive Learning for Neuroscience Meta-Analysis with Rich Text Representation
Coordinate-based meta-analysis (CBMA) is a common approach to synthesize information about human brain function across existing literature, enabling researchers to formulate hypotheses and contextualize new findings. However, automated CBMA tools face challenges such as inconsistent terminology, limited ability to analyze long texts, and difficulty capturing semantic meaning, as they still rely on bag-of-words approaches. In addition, sparse coordinate reporting distorts the activation distribution due to incomplete data. This paper introduces NeuroConText, an automated CBMA tool that bridges neuroscience text, brain location coordinates, and brain images by creating a shared latent space for encoding text and brain maps. Our method relies on a multi-objective loss combining contrastive and reconstruction terms. It leverages large language models (LLMs) to extract neuroscientific information from full-text articles and employs an LLM-based text augmentation strategy to improve generalization to short-text inputs. Quantitative and qualitative analyses demonstrate NeuroConText's ability to enhance text-to-brain retrieval performance and reconstruct brain maps from neuroscience texts. We also show that CBMA tools can infer brain activations in regions discussed in articles but absent from reported coordinates, potentially addressing the challenge of sparse coordinate reporting.

Focused ultrasound to the bilateral thalamus causally modulates human cognitive attention in a frequency- and intensity-dependent manner
The centromedian nucleus of the thalamus (CMT) is a core arousal center with potential for enhancing cognitive attention. While emergent focused ultrasound can reach this area, the stimulation paradigms which may enhance function in humans remain unknown. Here we performed bilateral stimulation of the CMT using a novel ultrasound neuromodulation wearable device using 3 distinct pulse frequencies. We found that a brief 25Hz stimulation enhanced reaction time in a in a directed attention Oddball task for at least 40 minutes. Pre-post task electrocortical EEG revealed a correlation between reaction time and the prevalence of arousal related alpha and theta cortical activity. Examination of dose dependence revealed bidirectional modulation of arousal state, with lower intensities preferentially enhancing cognitive function. Pre- and post-MRI scans showed no neuroradiological changes due to stimulation. Collectively, these findings demonstrate that targeted LIFU stimulation of the CMT can safely enhance cognitive function in healthy individuals with carefully designed parameters.

System-wide dissociation of reward and aversive dopaminergic signals
Dopamine is central to reinforcement learning, classically linked to reward prediction error signaling. However, recent findings suggest a more complex picture, with dopamine neurons responding to aversive or non-reward-related events and displaying diverse projection patterns. To investigate how dopamine release varies across the brain, we used multi-site fiber photometry to recors dopamine dynamics in mice performing tasks involving both rewarding and aversive outcomes. We found that while reward-related dopamine signals were broadly distributed, responses to aversive events were region-specific, enabling classification of projection targets from these dopamine dynamics. By examining the main axis of covariance of dopamine release across the brain, we found that reward prediction error signals are encoded by parallel manifolds, whereas aversive stimulus signals are encoded by orthogonal manifolds. Thus, our findings support a distributed, vector-valued model of dopaminergic signaling, in which anatomically and functionally distinct pathways contribute to encoding of reinforcement-related variables across the brain.

Efficient Generation of Expandable Dorsal Forebrain Neural Rosette Stem Cell Lines
Neural stem cells (NSCs) represent an interesting option for developing in vitro disease models and drug screening assays due to their differentiation capacity into neurons and glial cells. Additionally, NSCs are under investigation in on-going clinical trials for treatment of various human neurological disorders. NSCs can be isolated from the central nervous system or derived in vitro from human pluripotent stem cells (hPSCs). However, the current methods for generating NSCs typically include a phase of neural rosette formation and subsequent manual isolation of these tiny structures. As this is a laborious process characterized by operator-dependent variability and scalability challenges, there is a pressing need to develop optimized and scalable protocols to obtain pure NSC populations. In this study, we present a new method for generating highly pure and expandable dorsal forebrain FOXG1+OTX2+TLE4+SOX5+ neural rosette stem cell (NRSC) lines without the necessity for manual isolation of rosette structures. Our findings demonstrate the reproducibility of this protocol through the characterization of different NRSC lines over multiple passages, highlighting the robustness of the process. These NRSCs can be expanded for up to 12 passages without compromising their rosette-formation capacity or their initial dorsal forebrain identity. Furthermore, we show the differentiation capacity of these NRSCs to generate pure populations of TUBB3+ neurons, and under specific conditions, their ability to differentiate into early glial progenitor cells including GFAP+ astrocytes and O4+ oligodendrocytes. Collectively, these results show the capabilities of our protocol to generate an expandable NRSC population suitable for in vitro disease modeling and drug screening, while also suggesting a viable strategy for scalable NRSC production for clinical application.

Changes in social reward across adolescence in male mice
Background: In humans, adolescence is a time of dynamic behavioral and emotional changes, including a transient decrease in affect associated with being among family members. It is not clear if a similar change occurs in rodent species used to model human psychiatric disorders. Here, we investigated in the developmental profile of the reward value of interactions with siblings across adolescence in mice. Methods: Social conditioned place preference test was performed in male mice representing early (around postnatal day 33 [P33]), middle (P38) and late (P43) adolescence stages. Additionally, social interaction in the partition test and cocaine conditioned place preference were measured to assess the specificity of changes observed in social reward. Results: The reward value of interactions with siblings in adolescent male mice followed a similar course to that in humans: high in preadolescence, it decreased in mid-adolescence and returned to the initial level in late adolescence. No age-dependent changes in social interaction or in the preference for cocaine-conditioned context were detected. Limitations: The main limitation of our study is that it does not examine potential developmental changes in the proximate psychological mechanisms underlying social place preference. Conclusions: Taken together, these data show similarities between mice and humans in developmental changes in sensitivity to the rewarding effects of interactions with familiar kin.

Parallel and dynamic attention allocation during natural reading
During natural reading, attention constantly shifts across words, yet how linguistic properties (e.g., lexical frequency) impact the allocation of attention remains unclear. In this study, we co-registered MEG data and eye movements while participants read one-line sentences containing target words of either low or high lexical frequency. Using rapid invisible frequency tagging (RIFT), we simultaneously tracked attention to target and post-target words by flickering them at different frequencies. First, we provide neural evidence that attention was allocated simultaneously to both foveal target and parafoveal post-target words. Second, we found an early parafoveal lexical effect, whereby lower frequency targets demanded more attention prior to fixation, and, additionally, a foveal load effect whereby lower frequency targets reduced the amount of attention allocated to post-targets. Furthermore, flexibility in attention shifts between foveal and parafoveal processing correlated with individual reading speed. These results suggest attention is distributed across multiple words and is flexibly adjusted during reading.

Cholinergic synaptic plasticity shapes resilience and vulnerability to tau
Synaptic dysfunction is a hallmark of Alzheimer's disease (AD). Yet due to their plasticity, synapses may also adapt to early AD pathology. Using within-subject positron emission tomography scans targeting the vesicular acetylcholine transporter (VAChT) protein, tau, and amyloid in healthy older adults at risk for AD, we show that cholinergic neurons increase presynaptic VAChT levels when colocalized to tau, but not amyloid, with higher responses predicting resilience to cognitive decline over 10 years. In mice lacking forebrain VAChT, we demonstrate that cholinergic synaptic plasticity plays a causal role in sustaining cognitive flexibility and hippocampal structural integrity. Whole-brain single-nucleus RNA sequencing atlases reveal that cholinergic neurons upregulate a gene-network enriched for synaptic plasticity, with high centrality for the microtubule-associated protein tau (MAPT) gene. Our findings identify cholinergic synaptic plasticity as a critical mediator of resilience and vulnerability to tau in presymptomatic AD.

Distinguishing Lifelong Individual Differences from Divergent Aging Trajectories of Adult Brain Volumes
Differences in the volumes of brain structures between individuals are often linked to various conditions, including Alzheimer's disease, schizophrenia, and overall brain health. However, it remains unclear to what extent these differences reflect individual levels present at young adulthood or diverging aging trajectories at later ages. In this study, we analyze the aging dynamics of the volume of six brain structures based on MRI scans from a large cross-cohort longitudinal sample of cognitively healthy adults (n = 8,311 with 18,520 MRIs, ages from 18 to 97 years). From general assumptions about structural brain dynamics and measurement noise, a stochastic dynamical model was fit to the data to estimate both the variability and persistence of structural changes across adulthood. Using this model, we calculated how much of the variance in individual volumetric differences can be attributed to stable levels from young adulthood versus systematic changes at older ages, as well as the theoretical sensitivity of longitudinal studies to detect individual differences in changes. The findings were as follows: 1) Before age 60 years, inter-individual differences in neuroanatomical volumes almost exclusively reflect stable differences between individuals, while the influence from systematic differences in rate-of-change increases thereafter; up to 40 % of the variation being due to differences in change at 80 years. In contrast, ventricular volume reflects differences in change from early adulthood. 2) Current brain age-models are unlikely to be sensitive to detect differences in aging trajectories. 3) Imaging studies have a low reliability to detect inter-individual brain change before age 60. After 60 years, the study reliability increases sharply with longer intervals between scans and more modestly with additional intermediate observations. In conclusion, it is critical to distinguish stable levels from early adulthood from systematic differences in change when studying adult brain aging.

EEG Signature of Idiopathic Hypersomnia: Insights from Sleep Microarchitecture and Hypnodensity Metrics
Background and Objectives: Patients with idiopathic hypersomnia with long sleep time (IH) report daytime hypersomnolence despite prolonged sleep time and normal sleep macrostructure. As they often have non-restorative sleep, we investigated whether the structure of their sleep is abnormal. Methods: In polysomnography recordings from 80 IH participants and 48 controls, we quantified hypnodensity metrics across the night (macro level), periodic and aperiodic spectral properties, infraslow fluctuations of sigma power within the night (meso level), slow waves, sleep spindles and their clustering (microstructure). Multivariate machine-learning models were used to classify IH vs. control sleep. Results: Hypnodensity metrics were comparable between IH and controls, apart from more mixed wake/N1 sleep epochs in IH, and greater divergence between consecutive epochs of the same stage during NREM sleep in IH. Sigma power was increased in N2 sleep in IH and sleep spindles were more frequent and clustered. Slow wave density was higher in IH. Higher mean spindle cluster size correlated with higher Epworth Sleepiness Scale scores. Multivariate machine learning models incorporating these features achieved a balanced accuracy of 74% in distinguishing IH from controls. Discussion: While spindles and slow waves are typically associated with good sleep quality, they are increased in IH patients. This could reflect greater need for sleep and increased difficulty waking up in IH, which is also characterized by more mixed wake/N1 stages.

Brain network dynamics reflect psychiatric illness status and transdiagnostic symptom profiles across health and disease
The network organization of the human brain dynamically reconfigures in response to changing environmental demands, an adaptive process that may be disrupted in a symptom-relevant manner across psychiatric illnesses. Here, in a transdiagnostic sample of participants with (n=134) and without (n=85) psychiatric diagnoses, functional connectomes from intrinsic (resting-state) and task-evoked fMRI were decomposed to identify constraints on brain network dynamics across six cognitive states. Hierarchical clustering of 110 clinical, behavioral, and cognitive measures identified participant-specific symptom profiles, revealing four core dimensions of functioning: internalizing, externalizing, cognitive, and social/reward. Brain network dynamics were flattened across cognitive states in individuals with psychiatric illness and could be used to accurately separate dimensional symptom profiles more robustly than both case-control status and primary diagnostic grouping. A key role of inhibitory cognitive control and frontoparietal network interactions was uncovered through systematic model comparison. We provide novel evidence that brain network dynamics can accurately differentiate the extent that psychiatrically-relevant dimensions of functioning are exhibited across health and disease.

Neural responses prior to licking onset in the striatal matrix compartment in mice
Licking is a continuous tongue thrust observed during drinking in rodents and humans and is often studied as an essential tongue movement for feeding and swallowing. The striatum, a component of the basal ganglia, plays a critical role in licking onset; however, it is unclear how the two compartments of the striatum, the matrix and striosomes, contribute to the control of licking onset. In this study, we used male and female transgenic mice that selectively expressed Cre recombinase in matrix or striosome neurons and subjected them to operant conditioning based on licking of a spout, during which neuronal activity in both compartments was measured using fiber photometry. Only matrix neurons showed responses prior to licking onset. In addition, the matrix neural response before licking onset was larger when mice licked a spout ipsilateral to the recording hemisphere of the brain than that observed when licking the contralateral spout. This response was observed similarly in mice conditioned to receive a reward regularly and those conditioned to receive a reward randomly, suggesting that the response was unrelated to whether the reward was predictable or unpredictable. Matrix neural activity was negatively correlated with the number of licks during the water intake behavior following the first lick. These findings suggest that matrix neurons are involved in the preparatory process for licking onset as well as in the regulation of licking frequency during water intake.

The Effect of Previously Encountered Sensory Information on Neural Representations of Predictability: Evidence from Human EEG
Accumulating evidence suggests that the brain continuously monitors the predictability of rapidly evolving sound sequences, even when they are not behaviorally relevant. An increasing body of empirical evidence links sustained tonic M/EEG activity to evidence accumulation and tracking the predictability, or inferred precision, of the auditory stimulus. However, it remains unclear whether, and how, this process depends on auditory contextual memory. In the present EEG study, we examined neural responses to sound sequences across two experiments, and compared them to predictions from ideal observer models with varying memory spans. Stimuli were sequences of 50 ms long tone-pips. In Experiment 1 (N=26; both sexes), a regularly repeating sequence of 10 tones (REG) transitioned directly to a different regular sequence (REGxREGy). In Experiment 2 (N=28; both sexes), the same regular sequence was repeated after an intervening random segment (REGxINTREGx). Results from Experiment 2 revealed that the inferred predictability of the resumed REGx pattern was influenced by the preceding INT tones, even several seconds after they ended, indicating that the brain retains contextual memory over time. In contrast, neural responses in Experiment 1 were best explained by models with minimal memory. This dissociation implies that the brain can dynamically adjust its strategy based on inferred environmental structure: resetting context when interruptions signal change, and preserving context when patterns are likely to resume.

Comparing Brain-Behavior Relationships Across Dimensional, Tail-Sampled, and Propensity-Matched Models
Large population cohorts are needed to perform brain-wide association studies (BWAS), with evidence that sampling from the tails of a distribution increases effect sizes and improves reproducibility. However, studies rarely compare how variability in sample sociodemographic characteristics relates to imaging or behavioral phenotypes within BWAS. To address this gap, we derived estimates for brain-behavior associations using multivariate regression models, comparing effect sizes for dimensional, tail-sampled, and propensity matched groups. Data were obtained from the Adolescent Brain Cognitive Development (ABCD) Study. The independent variables were brain structural imaging phenotypes, with a range of biological and psychological outcomes as dependent variables. We found expected increases in the magnitude of effect sizes moving from full-sample dimensional models to tail-sampled group-based models. However, findings for the propensity-matched group models suggested a non-uniform impact on BWAS (i.e., both increased and decreased effect sizes). Results suggest that sampling from the tails of the distribution of measures of brain structure generally increases effect sizes across biological, clinical, and cognitive outcomes.

Sequential transcriptional gates in the thalamo-cortical circuit coordinate memory stabilization
The molecular mechanisms that enable memories to persist over long time-scales from days to weeks and months are still poorly understood. To develop insights we created a behavioral task where, by varying the frequency of learned associations, mice formed multiple memories but only consolidated some, while forgetting others, over the span of weeks. We then monitored circuit-specific molecular programs that diverge between consolidated and forgotten memories. We identified multiple distinct waves of transcription, i.e., cellular macrostates, specifically in the thalamo-cortical circuit, that defined memory persistence. Notably, a small set of transcriptional regulators orchestrated broad molecular programs that enabled entry into these macrostates. Targeted CRISPR-knockout studies revealed that while these transcriptional regulators had no effects on memory formation, they had prominent, causal, and strikingly time- dependent roles in memory stabilization. In particular, the calmodulin-dependent transcription factor Camta1 was required for initial memory maintenance over days, while Tcf4 and the histone methyl-transferase Ash1l were required later to maintain memory over weeks. These results identify a critical Camta1-Tcf4-Ash1l thalamo-cortical transcriptional cascade required for memory stabilization, and puts forth a model where the sequential, multi-step, recruitment of circuit-specific transcriptional programs enable memory maintenance over progressively longer time-scales.

Prenatal alcohol exposure dysregulates the expression of clock genes and alters rhythmic behaviour in mice
Foetal Alcohol Spectrum Disorders (FASD) refer to a range of adverse physical, behavioural, and cognitive effects caused by perinatal alcohol exposure. While cognitive impairments are well-documented, FASD has also been associated with sleep disturbances and circadian rhythm disruptions. This study aimed to examine the effects of perinatal alcohol exposure on circadian rhythms at behavioural and gene expression levels across two developmental stages (adolescence and adulthood) in both, male and female mice. Using a validated prenatal and lactation alcohol exposure (PLAE) protocol, we assessed circadian patterns of locomotor activity under free-running conditions and spatial memory performance during adolescence and adulthood. Additionally, we evaluated the impact of PLAE on circadian expression of clock and non-circadian genes involved in neurotransmission across key brain regions, including the medial prefrontal cortex and hippocampus. PLAE altered circadian rhythmicity and impaired spatial memory. Gene expression analyses revealed disrupted oscillatory patterns in clock genes and in genes related to plasticity and cognition, including those from the expanded endocannabinoid system (e.g. Cnr1, Dagla, Faah) and other neurotransmitter systems (e.g. Oprm1, Slc17a8, Drd1, Gabra1). These findings underscore the impact of early alcohol exposure on biological rhythms and neurobehavioral function, highlighting circadian dysregulation as a contributing factor to FASD.

Mental calculation: the fastest high-level cognitive ability of human beings?
High-level cognitive processing in human beings is thought to be slow. To test just how fast humans can process abstract knowledge, we analyze information rates associated with performances of top competitors in mental calculation. Even without taking the algorithms to perform the calculations into account, reading the numbers alone reaches information rates of around 90 bit/s in short tasks, eclipsing, to our knowledge, any previously reported value for high-level cognitive abilities. The execution speed of the underlying algorithms is as high as 70 bit/s, which in combination suggests that humans can process around 160 bit/s for a short time. Even for tasks of longer duration information rates remain remarkably high.

MegaTrack: a framework for the anatomically accurate and time-efficient virtual dissection and analysis of large-scale tractography datasets
The increasing prevalence of large-scale neuroimaging initiatives has created a need for efficient and anatomically accurate methods for analysing tractography data. Here, we present MegaTrack, a framework designed to combine the anatomical precision of manual dissections with the efficiency required for big data analysis. At its core, MegaTrack operates by normalising individual tractography datasets to a standard space, concatenating them into a single "mega" tractography dataset the user manually dissects before automatically extracting subject-specific tracts and metrics in native space. This approach permits identifying and extracting tracts not yet available in existing templates or automatic dissection tools. We validated this approach using multiple datasets and applications. Comparison with individual manual dissections showed high spatial agreement (weighted dice coefficient > 0.95) and strong correlations in tract-specific metrics (R2 > 0.9). In a longitudinal dataset, MegaTrack demonstrated improved reproducibility across time points and higher inter-rater reliability compared to manual dissections. In a motor neuron disease cohort, MegaTrack replicated known group differences in corticospinal tract microstructure with comparable sensitivity to manual dissections (p = 0.001) but with significantly reduced processing time. Finally, we showcase MegaTrack's scalability by creating a comprehensive white matter atlas from 140 healthy adults and demonstrate its application for lesion analysis in stroke patients. This framework is accompanied by an interactive online tool that allows users to explore these atlases and perform customised lesion analyses. The MegaTrack framework is a time-efficient solution for the anatomically precise analysis of large tractography datasets, enabling the rapid simultaneous dissection of multiple subjects while preserving individual anatomical features. The framework's ability to efficiently process large datasets makes it an excellent tool for generating training data for machine learning and deep learning algorithms in tractography analysis. This approach has broad applications in both research and clinical settings, from group comparisons to personalised lesion mapping, and can significantly contribute to the development of advanced automated tractography methods.

Human Myelin Spheres for In Vitro Oligodendrocyte Maturation, Myelination and Neurological Disease Modeling
Demyelinating diseases, such as multiple sclerosis, damage the protective myelin sheaths of the 36 central nervous system. The development of effective therapies has been hampered by the lack of models that accurately replicate human myelin biology. Here we present a novel method to generate human myelin spheres (MyS) by coculturing of hPSC-derived neuronal and oligodendrocyte precursor cells, to create myelinated neurons. Using multimodal analyses including confocal and (electron)microscopy, single-nuclei transcriptomics, lipidomics, and electrophysiology, we demonstrate myelination in MyS as early as six weeks into coculture. These myelinated structures mature over time into multilamellar and compacted myelin sheaths with lipid compositions and transcriptomic profiles mirror the temporal dynamics of in vivo human oligodendrocyte development and neuronal myelination, resembling those of late fetal/postnatal oligodendrocytes. By employing lysolecithin-induced demyelination and Rabies virus infection experiments, we demonstrate the potential of MyS as an innovative, physiologically relevant platform for studying myelin-related neurodegeneration and neuroinfection.

A new mouse mutant with a discrete mutation in Pcdhgc5 reveals that the Protocadherin γC5 isoform is not essential for dendrite arborization in the cerebral cortex
There are ~60 clustered protocadherin (cPcdh) isoforms expressed from three gene clusters (Pcdha, Pcdhb, Pcdhg) arrayed in tandem across nearly 1 Mb in mammals. cPcdhs are homophilic cell adhesion molecules (CAMs) critical for a host of neural developmental functions consistent with a role in cell-cell recognition. Indeed, isoforms make recognition modules in combination to generate recognition diversity far exceeding the ~60 individual CAMs. However, there is also growing evidence for specialized functions for specific isoforms, particularly the C-type isoforms found at the 3 prime ends of the Pcdha cluster (C1 and C2) and at the 3 prime end of the Pcdhg cluster ({gamma}C3, {gamma}C4, and {gamma}C5). We have previously described unique roles for {gamma}C3 in dendrite arborization in the cerebral cortex and neural circuit formation in the spinal cord, as well as for {gamma}C4 in neuronal survival. Here we report a new mouse mutant specifically targeting the Pcdhgc5 exon encoding {gamma}C5. Unlike the rest of the Pcdhg cluster, expression of this isoform does not begin until postnatal stages of mouse development, increasing in the second week of life, suggesting specialized roles. We found significant expression changes in gene pathways involved in synaptic activity, learning and memory, and cognition. Despite this, we saw no major disruption in the cerebral cortex in neuronal organization, survival, dendritic arborization, or synaptic protein expression in these mutants. This new model will be an important tool for future studies delineating specific functions for {gamma}C5.

NEUROGLIAL CB1 RECEPTORS CONTROL NAVIGATION STRATEGIES
Navigation and memory functions are essential for survival and are regulated by the hippocampus. These processes are tightly controlled, and one of the key modulators involved is the endocannabinoid system, particularly through the cannabinoid receptor type-1 (CB1). CB1 is widely expressed in various hippocampal cell types. While it is known that CB1 participates in memory processes, its specific roles in different cell types and how these roles may differ between sexes remain unclear. This study investigates how CB1 signaling in the hippocampus, in both, cell-type-specific and sex-dependent manner, contributes to navigation and memory. To this end, we selectively deleted CB1 receptors from neurons, CAMKII-expressing neurons, and astrocytes from the hippocampus of adult male and female mice. We then assessed its effect on a broad range of behaviors, including innate emotional responses, memory, navigation, and other hippocampus-related functions such as nesting. Deletion of CB1 in CAMKII-expressing neurons produced a pronounced effect in males, leading to increased anxiety and impairments in both reference and spatial memory. These mice also showed altered performance in the Barnes maze, relying less on spatial strategies. By contrast, females were less affected by this specific deletion. Interestingly, only deletion of CB1 from astrocytes led to spatial memory impairments in females, which also showed reduced LTP and a decreased reliance on spatial strategies in the Barnes maze. In conclusion, our findings show that neuronal CB1 receptors are critical for the spatial navigation strategy in males, while astrocytic CB1 receptors play a key role in memory processes both in males and females.

Success of GDNF-based treatment of Hirschsprung disease depends on NCAM1 signaling and various subtypes of enteric neural progenitors
Hirschsprung disease (HSCR) is a deadly congenital disorder where the enteric nervous system (ENS) is absent from the distal bowel. Current surgical treatment is generally life-saving but is often accompanied by long-term bowel problems and comorbidities. As alternative, we are developing a regenerative therapy based on rectal administration of the neurotrophic factor GDNF. We previously showed that administering GDNF enemas to HSCR mice soon after birth suffice to permanently induce a new ENS from tissue-resident neural progenitors. Here, we clarify the underlying mechanism using single-cell transcriptomics, signal transduction inhibitors and cell lineage tracing tools. Notably, we found that the neurogenic effect of GDNF is mediated by NCAM1, rather than by its canonical signaling receptor RET. We also unveiled the existence of multiple differentiation pathways that involve a larger than expected repertoire of tissue-resident neural progenitors, including a surprising one not derived from the usual neural crest.

Both the low-density lipoprotein receptor and apolipoprotein E define blood-borne high-density lipoprotein entry into the brain.
Data from epidemiological and genetic studies as well as animal experiments indicate that high-density lipoproteins (HDL) play a role in the pathogenesis of central nervous system (CNS) diseases. Apolipoprotein A-I, the major protein of HDL, has been immunolocalized in the brain although it is produced exclusively by the liver and intestine. We therefore investigated how HDL cross the blood-brain barrier (BBB), using both in vitro and in vivo approaches. In vitro, we found that HDL bind to, are internalized by, and are transported through human brain endothelial cells via mechanisms involving the scavenger receptor BI (SR-BI) and the low-density lipoprotein receptor (LDLR). Notably, we discovered that LDLR facilitates only the transport of HDL particles containing apolipoprotein E (apoE). In vivo, HDL injected into the bloodstream enter into the brain through brain endothelial cells, and accumulated in medulla, cerebellum, olfactory bulb, hippocampus and cortex. Further investigation in Ldlr knockout mice revealed region-specific changes in HDL accumulation with reduced levels in the medulla and mixture of midbrain/cortex/hippocampus, no change in the olfactory bulb, and increased levels in the cerebellum. Together, these findings provide new insight on the interaction of the lipoprotein metabolism between the periphery and CNS. For the first time, we show that brain endothelial receptors and HDL composition jointly dictate HDL crossing through the BBB and their localization within the brain.

Amygdalar Calcitonin Gene-Related Peptide Driven Effects of Cold Sensitivity Induced by Peripheral Neuropathy in Mice
The central nucleus of the amygdala (CeA) is a critical regulator of nociception, and its role in pain modulation depends on factors such as hemispheric location, neuropeptide release, and experimental model. Calcitonin gene-related peptide (CGRP) is a potent neuropeptide modulator within the CeA. Previous research has demonstrated its CeA nociceptive role in migraine, visceral, arthritic, and inflammatory pain murine models. The contribution of CeA CGRP to neuropathic pain is unclear. This study examined the effects of CGRP and its receptor antagonist, CGRP 8-37, in the CeA on mechanical and cold sensitivity in two mouse models of neuropathic pain: chemotherapy-induced peripheral neuropathy (CIPN) mediated by paclitaxel (PTX) and injury-induced neuropathy through the spared nerve injury (SNI) model. Mechanical and cold sensitivity were measured using the hindpaw von Frey and topical acetone drop assays, respectively. Neither CGRP nor CGRP 8-37 in the CeA had any significant effect on mechanical sensitivity in either neuropathic pain model. In the SNI-treated mice, CGRP infusion into either the left or right CeA reduced cold sensitivity in the left and right SNI-treated hindpaw, while CGRP 8-37 infusion into the left or right CeA increased cold sensitivity in the right SNI-treated hindpaw only. In PTX-treated mice, CGRP infusion into the left or right CeA decreased cold sensitivity of the contralateral paw only. These results suggest that CGRP in the CeA influences pain modulation in a complex manner that depends not only on the hemisphere and injury site, but also on the underlying cause of the neuropathic condition.

Optimizing short-channel regression in fNIRS: an empirical evaluation in a naturalistic multimodal paradigm
Functional Near-Infrared Spectroscopy (fNIRS) is increasingly favored for its portability and suitability for ecological paradigms, yet methodological standardization remains a challenge, especially regarding the optimal use of short-separation channels (SC) to remove systemic physiological noise. While SC signals are widely recognized for isolating extracerebral hemodynamics such as cardiac and respiratory artifacts, no consensus exists on how best to incorporate them into analysis pipelines, limiting comparability across studies. Here, we systematically investigate six SC regression strategies within a Generalized Linear Model (GLM) framework, using fNIRS data acquired from temporal and occipital cortices of 16 healthy adults during naturalistic auditory, visual, and audiovisual passive stimulation. These strategies varied in the number of SCs used, anatomical specificity, and the application of dimensionality reduction. Our results show that for oxygenated hemoglobin signals, processing data without SC regression yields uninterpretable outcomes, with widespread negative beta estimates and no detectable task-related activation, underscoring the crucial role of SC correction. Among correction methods, approaches pooling all SC signals without anatomical constraints consistently outperformed spatially constrained techniques mimicking limited SC availability. Furthermore, applying orthogonalization to the full set of SCs provided additional improvements by efficiently capturing shared systemic variance and reducing redundancy, enhancing detection of modality-specific cortical activations and condition contrasts. Finally, although the deoxygenated hemoglobin signal is inherently less sensitive to systemic noise, it benefited from the same SC regression strategies, supporting their applicability across chromophores. Overall, our findings highlight the essential role of SC regression in recovering physiologically meaningful signals in fNIRS and recommend including all available SC channels within the GLM, coupled with orthogonalization techniques, as a robust and generalizable best practice for denoising across diverse experimental designs and hardware configurations.

Longitudinal investigation of spatial memory and retinal parameters in a 5xFAD model of Alzheimers disease reveals differences dependent on genotype and sex
Significance: The retinal phenotype of Alzheimers disease (AD) is poorly understood. The connection between spatial memory and retinal phenotype is poorly investigated. Additionally, the influence of sex on the disease in mouse models is not sufficiently clear and requires further investigation. Aim: To investigate the retina and spatial memory of 5xFAD mouse models of AD by measuring retinal and behavioral parameters. Approach: A custom-built optical coherence tomography (OCT) system is used to image the retina of both eyes of 32 transgenic 5xFAD mice and 32 non-transgenic littermates over the course of 6 months (3-9 months of age) to investigate retinal parameters. The Morris Water Maze (MWM) test was performed to examine correlations between the retinal and spatial memory phenotype of the mouse model. Results: Data were acquired in the form of OCT reflectivity images and OCT angiograms as well as video recordings of the MWM test. Layer thickness and vascular density were calculated from the resulting data. Behavioral data was extracted from the videos acquired from the MWM. Total retinal and inner retinal layer thickness increased slightly over the measurement period, while outer retinal layer and retinal nerve fiber layer thickness showed no significant change. The correlation analysis between MWM and layer thickness data revelated a positive correlation between inner nuclear layer thickness and MWM test day parameters. Conclusions: OCT and MWM data revealed sex-based differences in the retinal phenotype of the 5xFAD mouse model, with changes in retinal thickness in different stages of the study and dissimilar correlations between retinal and spatial memory phenotype.

Pathogenic variants in autophagy-tethering factor EPG5 drive neurodegeneration through mitochondrial dysfunction and innate immune activation
The autophagy-tethering factor, ectopic P-granule 5 autophagy protein (EPG5), plays a key role in autophagosome-lysosome fusion. Impaired autophagy associated with pathogenic variants in EPG5 cause a rare devastating multisystem disorder known as Vici syndrome, which includes neurodevelopmental defects, severe progressive neurodegeneration and immunodeficiency. The pathophysiological mechanisms driving disease presentation and progression are not understood. In patient-derived fibroblasts and iPS cells differentiated to cortical neurons, we found that impaired mitophagy leads to mitochondrial bioenergetic dysfunction. Physiological Ca2+ signals resulted in paradoxical mitochondrial Ca2+ overload attributed to downregulation of MICU1/3. Ca2+ signals caused mitochondrial depolarisation, mtDNA release and activation of the cGAS-STING pathway, reversed by pharmacological inhibition of the mitochondrial permeability transition pore (mPTP) or of the STING pathway. Thus, we have identified multiple potential therapeutic targets driving disease progression associated with pathogenic EPG5 mutations, including impaired mitochondrial bioenergetics, mitochondrial Ca2+ overload, vulnerability to mPTP opening and activation of innate immune signalling.

Impact of Dysbiosis and Antiseizure Medication on Seizure Pathophysiology in a Viral Infection-Induced Epilepsy Model
Viral infections are associated with the development of seizures and epilepsy. Inflammation in the brain, particularly in the hippocampus, is thought to play a key role in orchestrating this process. We have previously demonstrated in mice that the gut microbiome influences seizure susceptibility following brain infection with Theiler's virus (TMEV). Further, gut dysbiosis significantly alters the antiseizure activity of carbamazepine (CBZ) in TMEV-infected mice with acute seizures. Thus, we herein sought to define how experimentally evoked intestinal dysbiosis influences hippocampal pathophysiology and neuroinflammation following acute symptomatic seizures in TMEV-infected mice, and whether acute CBZ treatment could further influence this neuropathology. Mice were pretreated with antibiotics or saline, followed by TMEV infection, and CBZ or vehicle administration (days 3-7 post-infection). Histological analyses were then performed on hippocampal tissue to quantify neuronal death, microgliosis, astrogliosis, and cellular proliferation after acute infection. While overall microglial reactivity did not markedly differ between groups, microglial proliferation was significantly increased in CA1 of CBZ-treated versus VEH-treated intact mice. Dysbiosis appeared to blunt this CBZ-induced microglial proliferation. Further, dysbiosis contributed to neuroprotection while also increasing neural proliferation within CA3, which may worsen disease outcomes due to aberrant migration and integration. The gut microbiome may thus prime CNS-specific immune responses in viral infection-induced seizures, opening the opportunity for potential GI-specific therapeutic interventions for seizures.

A novel frameshift mutation in Phosphoinositide 3-kinase regulatory subunit 1 (PIK3R1) causes immunodeficiency and Amyotrophic Lateral Sclerosis (ALS)
Mutations in PIK3R1, a regulatory subunit of Class I PI3K, are implicated in immune disorders and neurological conditions. We identified a novel heterozygous pathogenic frameshift mutation (c.1710dup) in PIK3R1 in a patient with common variable immunodeficiency who developed slowly progressive Amyotrophic Lateral Sclerosis. Induced pluripotent stem cells (iPSCs) and iPSC-derived motor neurons (iMNs) demonstrated that this mutation resulted in PIK3R1 haploinsufficiency, with downstream activation of AKT, disruption of neuronal electrical function and increased apoptosis in iPSC-derived motor neurons. Single-cell RNA sequencing (scRNA-seq) and pathway analysis of differentially expressed genes showed apoptosis pathways were upregulated in neuronal clusters from iMNs harboring the PIK3R1c.1710 dup mutation. Mutated iPSC-derived brain organoids were smaller than matched controls. scRNA-seq of brain organoids showed more active apoptosis in neuronal clusters of patient-derived brain organoids. These findings identify a critical and novel role for PIK3R1 haploinsufficiency in neuronal function and survival.

Unravelling neuromechanical constraints to finger independence
Intentional use of a single finger results in involuntary forces and movements among other fingers. Constraints to finger independence are attributed to both neural and mechanical factors, but the contribution of these factors is debated. We hypothesized that neural factors primarily constrain finger independence during isometric exertions whereas mechanical factors impose larger constraints during movements. We investigated changes in finger independence following a ring finger fatigue protocol. We assumed that with fatigue, the ability to actively transmit forces across fingers through neural pathways will be reduced but force transmission passively through mechanical pathways will remain unaffected. Participants performed isometric finger contractions and flexion-extension movements at baseline and following a ring finger fatigue protocol. At baseline, involuntary ring finger forces ranged from 7.3-16.5% MVC. Consistent with our predictions, involuntary ring finger forces decreased by 2.5-8.9% MVC following fatigue. In contrast, involuntary ring finger movement did not change or surprisingly in several cases, increased by greater than 10-20{degrees} following fatigue relative to baseline across movement tasks. Our findings demonstrate that the neuromechanical control of finger force versus motion are distinct from each other and can alter the constraints to finger independence in a task-dependent way.

Longitudinal Habituation and Novelty Detection neural responses from infancy to early childhood in The Gambia and UK
As infants and young children learn from and respond to their environment, their development is driven by their ability to filter out irrelevant stimuli and respond to salient stimuli. While sources and types of stimuli vary across cultural contexts, research to understand the neural mechanisms of these behaviors have largely focused on relatively homogeneous populations in high income settings. To address this lack of diverse representation the Brain Imaging for Global health project (BRIGHT) collected longitudinal data in The Gambia (N=204) and the UK (N=61). Here we present results of the Habituation and Novelty Detection (HaND) fNIRS neuroimaging task. Gambian infants showed persistent response suppression (Habituation) at all visits (from 5mo to 60mo) while Novelty Detection was only observed once infants reached 18 and 24mo. In the UK, infants only showed persistent habituation from 5-12mo, while the response was not evident at 18 and 24mo. Furthermore, in contrast to The Gambia, alongside the habituation patterns observed Uk infants showed novelty detection from 5-12mo. This is the first longitudinal description of the HaND response in individuals from different contextual backgrounds across such a broad age range and number of time points, revealing different patterns of specialization in The Gambia and UK.

Stressed Avoider rats show blunted sensitivity to alcohol's aversive effects: Potential contributions of the lateral habenula and lateral hypothalamus
Avoidance coping following stress exposure predicts heightened alcohol drinking. Similarly, blunted sensitivity to the aversive effects of alcohol facilitates increased drinking. However, the relationship between stress exposure, coping mechanism, and sensitivity to alcohol's aversive effects is unknown. In rats, predator odor stress increases alcohol intake in animals that show persistent avoidance of stress-paired stimuli, termed Avoiders. Here, we tested the hypothesis that Avoider rats have blunted sensitivity to alcohol's aversive effects using an alcohol-induced conditioned taste aversion (CTA) paradigm. After a single conditioning session, Non-Avoider rats acquired alcohol-induced CTA while Avoiders did not. Male rats across all groups eventually acquired alcohol CTA after four conditioning sessions. However, in females, only Non-Avoiders acquired alcohol-induced CTA. In male Non-Avoider rats, a single CTA-inducing dose of alcohol increased cFos expression in the lateral habenula (LHb), an important nucleus in aversion signaling. In male Avoiders, the same dose of alcohol decreased LHb cFos expression. cFos expression in the lateral hypothalamus (LH), which provides glutamatergic inputs to the LHb, was also diminished by alcohol in male Avoider rats. In females, alcohol had no effect on cFos cell counts in the LHb. However, in the LH, alcohol diminished cFos expression in female Non-Avoiders. Collectively, these findings suggest that stressed Avoider rats are hyposensitive to alcohol's aversive effects, which may facilitate their heightened alcohol drinking after stress. Sex- and stress group-specific differences in LH and LHb recruitment highlight these regions as candidates for mediating stress-induced changes in alcohol behaviors.