bioRxiv Subject Collection: Neuroscience's Journal

Lowering glucose enhances BACE1 activity and Aβ generation in mouse brain slice cultures
Numerous environmental risk factors are now recognised as contributors to the onset and progression of Alzheimer's disease (AD). It is probable that, in most instances, AD arises from a combination of genetic predisposition and environmental influences. In particular, there is a strong correlation between vascular impairment and dementia, yet the specific mechanisms by which vascular impairment and AD are linked, remain unknown. Hypoglycaemia can occur both due to vascular impairment, and due to fluctuating glucose levels in the context of diabetes, another risk factor for AD, and could potentially be involved in disease pathogenesis. To assess whether low glucose could contribute to the build-up of brain amyloid-{beta} (A{beta}) seen in AD, we exposed wildtype mouse organotypic hippocampal slice cultures (OHSCs) to varying glucose concentrations. Lowering glucose levels leads to an elevation in both A{beta}1-42 and A{beta}1-40 secreted into the culture medium, accompanied by an increased accumulation of A{beta} within the slice tissue. This effect is replicated in OHSCs derived from the TgCRND8 mouse model of overexpressed, mutant APP and in human SH-SY5Y cells. The heightened A{beta} levels are likely attributed to an upregulation of BACE1 activity, which is also observed with lowered glucose levels. In contrast, OHSCs subject to hypoxia exhibited no alterations in A{beta} levels whether singularly, or in combination of hypoglycaemia. Finally, we found that alternative energy sources such as pyruvate, fructose 1,6-bisphosphate, and lactate can alleviate heightened A{beta} levels, when given in combination with lowered glucose. This study underscores the capacity to induce an increase in A{beta} in a wildtype ex vivo system by selectively decreasing glucose levels.

Small animal brain surgery with neither a brain atlas nor a stereotaxic frame
Stereotaxic surgery is a cornerstone in brain research for the precise positioning of electrodes and probes, but its application is limited to species with available brain atlases and tailored stereotaxic frames. Addressing this limitation, we introduce an alternative technique for small animal brain surgery that requires neither an aligned brain atlas nor a standard stereotaxic frame. This method requires a high-contrast MRI scan of a specimen and access to a microCT scanner. The process involves attaching miniature markers to the skull, followed by CT scanning of the head. Subsequently, MRI and CT images are co-registered using standard image processing software and the targets for recordings in the brain are marked in the MRI image. During surgery, the animal's head is stabilized in any convenient orientation, and the probe's 3D position and angle are tracked using a multi-camera system. We have developed a software that utilizes the on-skull markers as fiducial points to align the CT/MRI 3D model with the surgical positioning system, and in turn instructs the surgeon how to move the probe to reach the targets within the brain. Our technique allows the execution of insertion tracks connecting two points in the brain. We successfully applied this method for neuropixels probe positioning in owls, quails, and mice, demonstrating its versatility and its potential to open new avenues for research in non-standard and novel animal models.

Frontal engagement in perceptual integration under low subjective visibility
We investigated how spatiotemporal neural dynamics underlying perceptual integration changed with the degree of conscious access to a set of backward-masked pacman-shaped inducers that generated the percept of an illusory triangle. We kept the stimulus parameters at a fixed near-threshold level throughout the experiment and recorded electroencephalography from participants who reported the orientation and subjective visibility of the illusory triangle on each trial. Our multivariate pattern analysis revealed that posterior and central regions initially used dynamic neural code and later switched to stable neural code. The transition from dynamic to stable neural code in posterior region occurred increasingly later and eventually disappeared with decreasing conscious access. Anterior region primarily used stable neural code which waned with decreasing conscious access, but increased at below-median visibility and remained even when stimulus awareness was minimal. These results demonstrate differential spatiotemporal neural dynamics underlying perceptual integration depending on conscious access and emphasize a unique role of anterior region in processing integrated shape information especially under low subjective visibility.

Alteration of nociceptive Schwann cells in a mouse model of peripheral neuropathy in prediabetic condition
Diabetic peripheral neuropathy (DPN) characterized by progressive and symmetrical sensory abnormalities is one of the earliest and main complications of diabetes. DPN is characterized by heterogeneous sensory symptoms such as chronic pain, tingling, burning or loss of sensation. Nociceptive Schwann cells (nSCs), a recently identified subtypes of dermal Schwann cells support terminal nerve fibers in mouse skin and contribute to mechanical sensation and neuropathic pain. While terminal nerve fibers density is basically evaluated in DPN models, there is currently few data about nSCs number and integrity during early stage of DPN. In the present study, we used a mouse model of prediabetes by using high-fat diet (HFD) fed mice to determine if there are quantitative differences in terminal nerve fiber density, nSCs number and cellular extensions between control and prediabetic neuropathic mice. In this study, we identified L1CAM as a reliable marker of nSCs currently characterized by the expression of S100beta and Sox10. Interestingly, we observed a decrease in intraepidermal nerve fiber density (IENFD) associated to a significant reduction of nSCs in the glabrous foot skin of neuropathic mice. Overall, this study identifies L1CAM as a new marker of nSCs and indicates that these cells are impaired during prediabetic peripheral neuropathy.

Subject-Agnostic Transformer-Based Neural Speech Decoding from Surface and Depth Electrode Signals
Objective: This study investigates speech decoding from neural signals captured by intracranial electrodes. Most prior works can only work with electrodes on a 2D grid (i.e., Electrocorticographic or ECoG array) and data from a single patient. We aim to design a deep-learning model architecture that can accommodate both surface (ECoG) and depth (stereotactic EEG or sEEG) electrodes. The architecture should allow training on data from multiple participants with large variability in electrode placements and the trained model should perform well on participants unseen during training. Approach: We propose a novel transformer-based model architecture named SwinTW that can work with arbitrarily positioned electrodes, by leveraging their 3D locations on the cortex rather than their positions on a 2D grid. We train both subject-specific models using data from a single participant as well as multi-patient models exploiting data from multiple participants. Main Results: The subject-specific models using only low-density 8x8 ECoG data achieved high decoding Pearson Correlation Coefficient with ground truth spectrogram (PCC=0.817), over N=43 participants, outperforming our prior convolutional ResNet model and the 3D Swin transformer model. Incorporating additional strip, depth, and grid electrodes available in each participant (N=39) led to further improvement (PCC=0.838). For participants with only sEEG electrodes (N=9), subject-specific models still enjoy comparable performance with an average PCC=0.798. The multi- subject models achieved high performance on unseen participants, with an average PCC=0.765 in leave-one-out cross-validation. Significance: The proposed SwinTW decoder enables future speech neuropros- theses to utilize any electrode placement that is clinically optimal or feasible for a particular participant, including using only depth electrodes, which are more routinely implanted in chronic neurosurgical procedures. Importantly, the generalizability of the multi-patient models suggests the exciting possibility of developing speech neuropros- theses for people with speech disability without relying on their own neural data for training, which is not always feasible.

Environmental complexity modulates information processing and the balance between decision-making systems
Decision-making relies on dynamic interplay between multiple neural circuits and decision-making systems integrating past experiences, current goals, and environmental demands. Past studies of rodent decision-making have largely occurred in simple environments and on isolated brain areas. This leaves unclear the impact of environmental complexity on the interaction between multiple brain areas to set adaptive strategies. To fill this gap, we either recorded neural activity across the key regions of hippocampus (HC), dorsolateral striatum (DLS), and medial prefrontal cortex (mPFC) or chemogenetically inactivated mPFC in a separate cohort while rats foraged for food under changing rules in differently complex environment. Environmental complexity increased behavioral variability, lengthened HC nonlocal sequences, and introduced intermediary subgoals. We found contrasting representations between DLS and HC, supporting a competition between decision systems. mPFC activity was indicative of setting this balance, in particular predicting nonlocal HC coding. Inactivating mPFC impaired short-term behavioral adaptation and produced long-term deficits balancing decision systems. Our findings reveal the dynamic nature of decision-making systems and how environmental complexity modulates their engagement with implications for behavior within naturalistic environments.

Pretrauma cognitive traits predict trauma-induced fear generalization and associated prefrontal functioning in a longitudinal model of posttraumatic stress disorder
Posttraumatic stress disorder (PTSD) is a chronic psychiatric condition that develops in susceptible individuals exposed to traumatic stress, challenging clinicians to identify risk factors and mechanisms for mitigating vulnerability. Here we investigated behavioral predictors of high fear generalization, a core PTSD symptom, and its neural correlates longitudinally in rats. In a comprehensive behavioral test battery of emotional and cognitive function, pretrauma lower operant learning performance emerged as high predictor of fear generalization following trauma. Posttrauma operant training facilitated fear extinction, suggesting an overlap in neural circuits governing operant learning and fear expression. Neuronal activity mapping revealed significant changes in the medial prefrontal cortex (mPFC) in high fear generalizers, with alterations in CRH/VIP+ interneuron functioning. Silencing prefrontal Crh expression after fear memory consolidation enhanced mPFC activation and reduced fear expression, favoring resilience. These findings highlight operant learning and mPFC alterations as vulnerability markers and mediators of excessive fear generalization, with implications for prevention and targeted therapy in PTSD.

Sensory and perceptual decisional processes underlying the perception of reverberant auditory environments
Reverberation, a ubiquitous feature of real-world acoustic environments, exhibits statistical regularities that human listeners leverage to self-orient, facilitate auditory perception, and understand their environment. Despite the extensive research on sound source representation in the auditory system, it remains unclear how the brain represents real-world reverberant environments. Here, we characterized the neural response to reverberation of varying realism by applying multivariate pattern analysis to electroencephalographic (EEG) brain signals. Human listeners (12 male and 8 female) heard speech samples convolved with real-world and synthetic reverberant impulse responses and judged whether the speech samples were in a 'real' or 'fake' environment, focusing on the reverberant background rather than the properties of speech itself. Participants distinguished real from synthetic reverberation with ~75% accuracy; EEG decoding reveals a multistage decoding time course, with dissociable components early in the stimulus presentation and later in the peri-offset stage. The early component predominantly occurred in temporal electrode clusters, while the later component was prominent in centro-parietal clusters. These findings suggest distinct neural stages in perceiving natural acoustic environments, likely reflecting sensory encoding and higher-level perceptual decision-making processes. Overall, our findings provide evidence that reverberation, rather than being largely suppressed as a noise-like signal, carries relevant environmental information and gains representation along the auditory system. This understanding also offers various applications; it provides insights for including reverberation as a cue to aid navigation for blind and visually impaired people. It also helps to enhance realism perception in immersive virtual reality settings, gaming, music, and film production.

Adaptation to visual sparsity enhances responses to infrequent stimuli
Sensory systems adapt their response properties to the statistics of their inputs. For instance, visual systems adapt to low-order statistics like mean and variance to encode the stimulus efficiently or to facilitate specific downstream computations. However, it remains unclear how other statistical features affect sensory adaptation. Here, we explore how Drosophila's visual motion circuits adapt to stimulus sparsity, a measure of the signal's intermittency not captured by low-order statistics alone. Early visual neurons in both ON and OFF pathways alter their responses dramatically with stimulus sparsity, responding positively to both light and dark sparse stimuli but linearly to dense stimuli. These changes extend to downstream ON and OFF direction-selective neurons, which are activated by sparse stimuli of both polarities, but respond with opposite signs to light and dark regions of dense stimuli. Thus, sparse stimuli activate both ON and OFF pathways, recruiting a larger fraction of the circuit and potentially enhancing the salience of infrequent stimuli. Overall, our results reveal visual response properties that increase the fraction of the circuit responding to sparse, infrequent stimuli.

Local, calcium- and reward-based synaptic learning rule that enhances dendritic nonlinearities can solve the nonlinear feature binding problem
This study explores the computational potential of single striatal projection neurons (SPN), emphasizing dendritic nonlinearities and their crucial role in solving complex integration problems. Utilizing a biophysically detailed multicompartmental model of an SPN, we introduce a calcium-based, local synaptic learning rule that leverages dendritic plateau potentials. According to what is known about excitatory corticostriatal synapses, the learning rule is governed by local calcium dynamics from NMDA and L-type calcium channels and dopaminergic reward signals. In addition, we incorporated metaplasticity in order to devise a self-adjusting learning rule which ensures stability for individual synaptic weights. We demonstrate that this rule allows single neurons to solve the nonlinear feature binding problem (NFBP), a task traditionally attributed to neuronal networks. We also detail an inhibitory plasticity mechanism, critical for dendritic compartmentalization, further enhancing computational efficiency in dendrites. This in silico study underscores the computational capacity of individual neurons, extending our understanding of neuronal processing and the brain's ability to perform complex computations.

Reliability of brain metrics derived from a Time-Domain Functional Near-Infrared Spectroscopy System
With the growing interest in establishing brain-based biomarkers for precision medicine, there is a need for noninvasive, scalable neuroimaging devices that yield valid and reliable metrics. Kernel's second-generation Flow2 Time-Domain Functional Near-Infrared Spectroscopy (TD-fNIRS) system meets the requirements of noninvasive and scalable neuroimaging, and uses a validated modality to measure brain function. In this work, we investigate the test-retest reliability (TRR) of a set of metrics derived from the Flow2 recordings. We adopted a repeated-measures design with 49 healthy participants, and quantified TRR over multiple time points, different headsets, and different experimental conditions including a resting state, a sensory, and a cognitive task. Results demonstrated high reliability in resting state features including hemoglobin concentrations, head tissue light attenuation, amplitude of low frequency fluctuations, and functional connectivity. Additionally, passive auditory and Go/No-Go inhibitory control tasks each exhibited similar activation patterns across days. Notably, areas with the highest reliability were in auditory regions during the auditory task, and right prefrontal regions during the Go/No-Go task, consistent with prior literature. This study underscores the reliability of Flow2-derived metrics, supporting its potential to actualize the vision of using brain-based biomarkers for diagnosis, treatment selection and treatment monitoring of neuropsychiatric and neurocognitive disorders.

Distinct changes to hippocampal and medial entorhinal circuits emerge across the progression of cognitive deficits in epilepsy
Temporal lobe epilepsy (TLE) causes pervasive and progressive memory impairments, yet the specific circuit changes that drive these deficits remain unclear. To investigate how hippocampal-entorhinal dysfunction contributes to progressive memory deficits in epilepsy, we performed simultaneous in vivo electrophysiology in hippocampus (HPC) and medial entorhinal cortex (MEC) of control and epileptic mice 3 or 8 weeks after pilocarpine-induced status epilepticus (Pilo-SE). We found that HPC synchronization deficits (including reduced theta power, coherence, and altered interneuron spike timing) emerged within 3 weeks of Pilo-SE, aligning with early-onset, relatively subtle memory deficits. In contrast, abnormal synchronization within MEC and between HPC-MEC emerged later, by 8 weeks after Pilo-SE, when spatial memory impairment was more severe. Furthermore, a distinct subpopulation of MEC layer 3 excitatory neurons (active at theta troughs) was specifically impaired in epileptic mice. Together, these findings suggest that hippocampal-entorhinal circuit dysfunction accumulates and shifts as cognitive impairment progresses in TLE.

PICK1 links KIBRA and AMPA receptors in coiled-coil-driven supramolecular complexes
The human memory-associated protein KIBRA regulates synaptic plasticity and trafficking of AMPA-type glutamate receptors, and is implicated in multiple neuropsychiatric and cognitive disorders. How KIBRA forms complexes with and regulates AMPA receptors remains unclear. Here, we show that KIBRA does not interact directly with the AMPA receptor subunit GluA2, but that PICK1, a key regulator of AMPA receptor trafficking, can serve as a bridge between KIBRA and GluA2. We identified structural determinants of KIBRA-PICK1-AMPAR complexes by investigating interactions and cellular expression patterns of different combinations of KIBRA and PICK1 domain mutants. We find that the PICK1 BAR domain, a coiled-coil structure, is sufficient for interaction with KIBRA, whereas mutation of the BAR domain disrupts KIBRA-PICK1-GluA2 complex formation. In addition, KIBRA recruits PICK1 into large supramolecular complexes, a process which requires KIBRA coiled-coil domains. These findings reveal molecular mechanisms by which KIBRA can organize key synaptic signaling complexes.

Decoding the Cognitive map: Learning place cells and remapping
Hippocampal place cells are known for their spatially selective firing and are believed to encode an animal's location while forming part of a cognitive map of space. These cells exhibit marked tuning curve and rate changes when an animal's environment is sufficiently manipulated, in a process known as remapping. Place cells are accompanied by many other spatially tuned cells such as border cells and grid cells, but how these cells interact during navigation and remapping is unknown. In this work, we build a normative place cell model wherein a neural network is tasked with accurate position reconstruction and path integration. Motivated by the notion of a cognitive map, the network's position is estimated directly from its learned representations. To obtain a position estimate, we propose a non-trainable decoding scheme applied to network output units, inspired by the localized firing patterns of place cells. We find that output units learn place-like spatial representations, while upstream recurrent units become boundary-tuned. When the network is trained to perform the same task in multiple simulated environments, its place-like units learn to remap like biological place cells, displaying global, geometric and rate remapping. These remapping abilities appear to be supported by rate changes in upstream units. While the model does not learn grid-like units, its place cell centers form clusters organized in a hexagonal lattice in open fields. This suggests a potential mechanism for the interaction between place cells, border cells, and grid cells. Our model provides a normative framework for learning spatial representations previously reserved for biological place cells, providing new insight into place cell field formation and remapping.

Assessing Individual Sensitivity to the Thermal Grill Illusion: A Two-Dimensional Adaptive Psychophysical Approach
In the thermal grill illusion (TGI), the spatial alternation of non-noxious warm and cold temperatures elicits burning sensations that resemble the presence of noxious stimuli. Previous research has largely relied on the use of specific temperature values (i.e., 20C and 40C) to study this phenomenon in both healthy individuals and patient populations. However, this methodology fails to account for inter-individual differences in thermal sensitivity, limiting the precision with which TGI responses can be evaluated across diverse populations. To address this gap, we created a Two-Dimensional Thermal Grill Calibration (2D-TGC) protocol, enabling an efficient and precise estimation of the combinations of warm and cold temperatures needed to elicit burning sensations tailored to each individual. By applying the 2D-TGC protocol in 43 healthy participants, we demonstrated key findings: (1) The TGI can be thresholded using an adaptive psychophysical method. (2) Multiple combinations of warm and cold temperatures can elicit this phenomenon. (3) The protocol facilitated the identification of temperature combinations that elicit TGI with varying levels of probability, intensity, and perceived quality ranging from freezing cold to burning hot. (4) TGI responsivity can be quantified as a continuous variable, moving beyond the conventional classification of individuals as responders vs. non-responders based on arbitrary temperature values. The 2D-TGC offers a comprehensive approach to investigate the TGI across populations with altered thermal sensitivity, and can be integrated with other methods (e.g., neuroimaging) to elucidate the mechanisms responsible for perceptual illusions in the thermo-nociceptive system.

Early-life stress alters chromatin modifications in VTA to prime stress sensitivity
Early-life stress increases sensitivity to subsequent stress, which has been observed among humans, other animals, at the level of cellular activity, and at the level of gene expression. However, the molecular mechanisms underlying such long-lasting sensitivity are poorly understood. We tested the hypothesis that persistent changes in transcription and transcriptional potential were maintained at the level of the epigenome, through changes in chromatin. We used a combination of bottom-up mass spectrometry, viral-mediated epigenome-editing, behavioral quantification, and RNA-sequencing in a mouse model of early-life stress, focusing on the ventral tegmental area (VTA), a brain region critically implicated in motivation, reward learning, stress response, and mood and drug disorders. We find that early-life stress in mice alters histone dynamics in VTA and that a majority of these modifications are associated with an open chromatin state that would predict active, primed, or poised gene expression, including enriched histone-3 lysine-4 methylation and the H3K4 monomethylase Setd7. Mimicking ELS through over-expression of Setd7 and enrichment of H3K4me1 in VTA recapitulates ELS-induced behavioral and transcriptional hypersensitivity to future stress. These findings enrich our understanding of the epigenetic mechanisms linking early-life environmental experiences to long-term alterations in stress reactivity within the brain's reward circuitry, with implications for understanding and potentially treating mood and anxiety disorders in humans.

Joint contribution of adaptation and neuronal population recruitment to response level in visual area MT: a computational model
Adaptation is a form of short-term plasticity triggered by prolonged exposure to a stimulus, often resulting in altered perceptual sensitivity to stimulus features through a reduction in neuronal firing rates. Experimental studies have explored adaptation to bistable stimuli, specifically a stimulus comprising inward-moving plaids that can be perceived as either a grating moving coherently downward or two plaids moving incoherently through each other. Functional magnetic resonance imaging (fMRI) recordings have shown higher activity during incoherent perception and lower activity during coherent stimulus perception. There are two potential explanations for the underlying neural mechanisms: a weaker coherent stimulus response may result from stronger adaptation to coherent versus incoherent motion, or a stronger incoherent stimulus response could stem from the involvement of more neural populations to represent motion in more directions. Here, we employ a computational model of visual neurons with and without firing rate adaptation to test these hypotheses. By simulating the mean activity of a network of thirty-two columnar populations of visual area MT, each tuned to one direction of motion, we investigate the impact of firing rate adaptation on the blood-oxygen-level-dependent (BOLD) signal generated by the network in response to coherent and incoherent stimuli. Our results replicate the experimental curves both during and after stimulus presentation only when the model includes adaptation, highlighting the importance of this mechanism. However, our findings reveal that the response to incoherent motion is larger than the response to coherent motion for a wide variety of stimulus parameters and adaptation regimes, suggesting that the observed reduced response to coherent stimuli is most likely due to the activation of smaller neuronal populations, in alignment with the second hypothesis. Hence, adaptation and differential neuronal recruitment work together to give rise to the observed hemodynamic responses. This computational work sheds light on experimental results and enriches our understanding of the mechanisms involved in neural adaptation, particularly in the context of heterogeneous neuronal populations.

Characterizing an electronic-robotic targeting platform for precise and fast brain stimulation with multi-locus transcranial magnetic stimulation
Background: Multi-locus TMS (mTMS) enables precise electronic control of brain stimulation targeting, eliminating the need for physical coil movement. However, with a small number of coils, the stimulation area is constrained, and manually handling the coil array is cumbersome. Combining electronic mTMS targeting with robotics will enable automated, user-independent, and precise brain stimulation protocols. Objective: Characterizing an open-source electronic-robotic mTMS platform for rapid and accurate brain stimulation targeting. Methods: We developed an automated robotic mTMS positioning platform. The accuracy of the system was quantified with a TMS characterizer that measures the TMS-induced electric field on a spherical cortex model. We used a 5-coil mTMS device equipped with a set of five coils coupled to a collaborative robot. The induced electric-field distortion generated by robot coupling was evaluated for each coil. We compared the accuracy of robotic-electronic targeting by repositioning the mTMS coil set with the robotic and the conventional manual positioning. Results: Our collaborative robot-based system offers submillimeter precision and autonomy in positioning mTMS coil sets. The electronic-robotic mTMS platform was approximately 1.8 mm and 1.0 degrees more accurate than the conventional manual positioning. Integrating robotics and mTMS automates brain stimulation procedures, resulting in minimal reliance on user expertise and subjective analysis. Conclusion: Our open-source platform combining rapid mTMS targeting with robotic precision enhances the safety and reproducibility of brain stimulation techniques, enabling more efficient and reliable outcomes than previous techniques.

Optimal motion-in-depth estimation with natural stimuli
Estimating the motion of objects in depth is important for behavior, and is strongly supported by binocular visual cues. To understand both how the brain should estimate motion in depth and how natural constraints shape and limit performance, we develop image-computable ideal observer models from naturalistic binocular video clips of two 3D motion tasks. The observers spatio-temporally filter the videos, and non-linearly decode 3D motion from the filter responses. The optimal filters and decoder are dictated by the task-relevant natural image statistics, and are specific to each task. Multiple findings emerge. First, two distinct filter types are spontaneously learned for each task. For 3D speed estimation, filters emerge for processing either changing disparities over time (CDOT) or interocular velocity differences (IOVD), cues used by humans. For 3D direction estimation, filters emerge for discriminating either left-right or towards-away motion. Second, the filter responses, conditioned on the latent variable, are well-described as jointly Gaussian, and the covariance of the filter responses carries the information about the task-relevant latent variable. Quadratic combination is thus necessary for optimal decoding, which can be implemented by biologically plausible neural computations. Finally, the ideal observer yields non-obvious, and in some cases counter-intuitive, patterns of performance like those exhibited by humans. Important characteristics of human 3D motion processing and estimation may therefore result from optimal information processing in the early visual system.

Open-Source Tools to Analyze Temporal and Spatial Properties of Local Field Potentials
Analysis of local field potentials (LFPs) is important for understanding how ensemble neurons function as a network in a specific region of the brain. Despite the availability of tools for analyzing LFP data, there are some missing features such as analysis of high frequency oscillations (HFOs) and spatial properties. In addition, accessibility of most tools is restricted due to closed source code and/or high costs. To overcome these issues, we have developed two freely available tools that make temporal and spatial analysis of LFP data easily accessible. The first tool, hfoGUI (High Frequency Oscillation Graphic User Interface), allows temporal analysis of LFP data and scoring of HFOs such as ripples and fast ripples which are important in understanding memory function and neurological disorders. To complement the temporal analysis tool, a second tool, SSM (Spatial Spectral Mapper), focuses on the spatial analysis of LFP data. The SSM tool maps the spectral power of LFPs as a function of subject's position in a given environment allowing investigation of spatial properties of LFP signal. Both hfoGUI and SSM are open-source tools that have unique features not offered by any currently available tools, and allow visualization and spatio-temporal analysis of LFP data.

When visual attention is divided in the flash-lag effect
The flash-lag effect (FLE) is the perceived lagging behind of a flash physically aligned to a continuously moving object. The illusion is attributed to a compensatory mechanism of motion extrapolation, which ensures that the perceived position of a moving object aligns with its real-time position despite neural processing delays. While several studies have demonstrated that attention can modulate the FLE, the precise role of attention in the extrapolation process remains elusive. Thus, in the current study, we sought to disentangle the influence of visual attention by manipulating the amount of attention allocated to moving stimuli in different locations. By directing attention to one, two, three, or four stimuli presented in different quadrants across trials, we measured the trial-wise FLE to investigate potential FLE magnitude or variability modulations under different attention conditions. Our results showed that FLE magnitudes were significantly larger when attention was divided among two, three, or four stimuli than when attention was focused on one stimulus. Surprisingly, FLE variability showed no difference across attention conditions. These findings show that the compensatory mechanisms for neural processing delays in dynamic environments are modulated by attention to enable efficient processing of multiple objects simultaneously.

Defects in exosome biogenesis are associated with sensorimotor defects in zebrafish vps4a mutants
Mutations in human VPS4A are associated with neurodevelopmental defects, including motor delays and defective muscle tone. VPS4A encodes a AAA-ATPase that is required for membrane scission, but how mutations in VPS4A lead to impaired control of motor function is not known. Here we identified a mutation in zebrafish vps4a, T248I, that affects sensorimotor transformation. In biochemical experiments we show that the T248I mutation reduces the ATPase activity of Vps4a and disassembly of its substrate, ESCRT filaments, which mediate membrane scission. Consistent with the established role for Vps4a in the endocytic pathway and exosome biogenesis, vps4aT248I mutants have enlarged endosomal compartments in the CNS and decreased numbers of circulating exosomes. Resembling the central form of hypotonia in human VPS4A patients, motor neurons and muscle cells are unaffected in mutant zebrafish as they react robustly to touch. Unlike somatosensory function, optomotor responses, vestibulospinal (VS), and acoustic startle reflexes are severely impaired in vps4aT248I mutants, indicating a greater sensitivity of these circuits to the T248I mutation. ERG recordings indicate that visual ability is largely reduced in the mutants, however, in vivo imaging of tone-evoked responses in the inner ear and ascending auditory pathway show comparable activity. Further investigation of central pathways in vps4aT248I mutants revealed that sensory cues failed to fully activate neurons in the VS and medial longitudinal fasciculus (MLF) nuclei that directly innervate motor neurons. Our results suggest that a defect in sensorimotor transformation underlies the profound yet selective effects on motor reflexes resulting from the loss of membrane scission mediated by Vps4a.

Enhancer-targeted CRISPR-Activation Rescues Haploinsufficient Autism Susceptibility Genes
Autism Spectrum Disorder (ASD) is a highly heritable condition with diverse clinical presentations. Approximately 20% of ASD's genetic susceptibility is imparted by de novo mutations of major effect, most of which cause haploinsufficiency. We mapped enhancers of two high confidence autism genes - CHD8 and SCN2A and used CRISPR-based gene activation (CRISPR-A) in hPSC-derived excitatory neurons and cerebral forebrain organoids to correct the effects of haploinsufficiency, taking advantage of the presence of a wildtype allele of each gene and endogenous gene regulation. We found that CRISPR-A induced a sustained increase in CHD8 and SCN2A expression in treated neurons and organoids, with rescue of gene expression levels and mutation-associated phenotypes, including gene expression and physiology. These data support gene activation via targeting enhancers of haploinsufficient genes, as a therapeutic intervention in ASD and other neurodevelopmental disorders.

Neurexin drives C. elegans avoidance behavior independently of its post-synaptic binding partner Neuroligin
Neurexins and their canonical binding partners, neuroligins, are localized to neuronal pre-, and post-synapses, respectively, but less is known about their role in driving behaviors. Here, we use the nematode C. elegans to show that neurexin, but not neuroligin, is required for avoiding specific chemorepellents. We find that adults with knockouts of the entire neurexin locus exhibit a strong avoidance deficit in response to glycerol and a weaker defect in response to copper. Notably, the C. elegans neurexin (nrx-1) locus, like its mammalian homologs, encodes multiple isoforms, a and g. Using isoform-specific mutations, we find that the g isoform is selectively required for glycerol avoidance. Next, we used transgenic rescue experiments to show that this isoform functions at least partially in the nervous system. We also confirm that the transgenes are expressed in the neurons and observe protein accumulation in neurites. Furthermore, we tested whether these mutants affect the behavioral responses of juveniles. We find that juveniles (4th larval stages) of mutants knocking out the entire locus or the a-isoforms, but not g-isoform, are defective in avoiding glycerol. These results suggest that the different neurexin isoforms affect chemosensory avoidance behavior in juveniles and adults, providing a general principle of how isoforms of this conserved gene affect behavior across species.

Functional analysis of the epilepsy gene Pcdh19 using a novel GFP-reporter mouse model
Mutations in the X-linked gene PCDH19 are the cause of PCDH19-Clustering epilepsy, an infantile-onset disorder characterized by seizures and intellectual disabilities. Although several intra and extracellular functions of PCDH19 have been identified, the spatiotemporal impact of Pcdh19 deletion in vivo is poorly understood. To investigate the consequences of eliminating Pcdh19 in specific cell and brain regions, we generated a novel Pcdh19 floxed mouse with a GFP reporter (Pcdh19-cKO-GFP). Using Pcdh19-cKO-GFP and Syn1-Cre mouse lines we demonstrated that Pcdh19 elimination in neurons leads to abnormal hippocampal neurogenesis and impaired mouse behaviour. To assess the impact of region-specific elimination of Pcdh19 on brain physiology we used a Gfap-Cre mice line. Specific Pcdh19 deletion in the hippocampus resulted in increased neurogenesis and decreased memory formation. Finally, we assessed the feasibility of using our conditional mouse model for stage-specific Pcdh19 elimination during embryogenesis using a Dox-inducible Cre-deletor line. Taken together, these results demonstrate the utility of our unique Pcdh19-cKO-GFP mouse model to investigate PCDH19 function in brain physiology and pathology.

Reduced GABA transmission onto ventral tegmental area dopamine neurons underlies vulnerability for hyperactivity in a mouse model of Anorexia Nervosa
Anorexia nervosa (AN) has the highest mortality among psychiatric diseases. Hyperactivity is a persistent symptom, which is difficult to control for patients and a major barrier to recovery as it interferes with weight gain. Alteration of mesolimbic dopamine transmission has been hypothesized as a critical factor for the development and maintenance of the disease and for hyperactivity. At what level the changes in dopamine occur in anorexic states and whether local mesolimbic neurocircuit plasticity is causally involved remains unclear. Especially the role of local GABA control over dopamine neurons, a powerful regulator of the dopamine system, in an AN context is unknown. We hypothesize that combining caloric restriction with exercise, such as in the activity-based anorexia (ABA) model, alters dopamine transmission via GABA disinhibition that, in turn, facilitates the expression of maladaptive behaviors such as hyperactivity. Therefore, we characterized the impact of the ABA model on plasticity of the dopamine reward system. In ex-vivo brain slices of mice exposed to this model, ventral tegmental area dopamine (VTADA) neurons displayed a higher firing frequency compared to control mice supporting that the midbrain dopamine system undergoes plasticity. This coincided with reduced GABAergic transmission on VTADA neurons. This reduction was at least in part attributable to local VTA GABA (VTAGABA) neurons. Indeed, VTAGABA neurons were less excitable, displayed a lower firing frequency and a lower probability of release onto VTADA neurons. Restoring the excitability of VTAGABA neurons via chemogenetic activation rescued mice from starvation, by decreasing running wheel activity. In summary, we found that the anorexic state leads to dysregulation of VTAGABA transmission on VTADA neurons that reinforces maladaptive behaviors such as excessive exercise. We uncovered a new mechanism linked to the disturbed dopamine system in ABA-exposed animals, identifying a hitherto unknown role of decreased local GABAergic control over VTA dopamine neuron output.

Decreasing hearing ability does not lead to improved visual speech extraction as revealed in a neural speech tracking paradigm
The use of visual speech is thought to be especially important in situations where acoustics are unclear and in individuals with hearing impairment. To investigate this in a neural speech tracking paradigm, we measured MEG in sixty-seven mid- to old-age individuals during audiovisual (AV), audio-only (A), and visual-only (V) speech in the context of face masks. First, we could extend previous findings by showing that not only in young normal-hearing individuals but also in aging individuals with decreasing hearing ability the brain is superior in neurally tracking the acoustic spectrogram in AV compared to A presentations, especially in multi-speaker situations. The addition of visual lip movements further increases this benefit. Second, we could show that neural speech tracking in individuals with lower levels of hearing ability is affected more by face masks. However, in this population, the effect seems to be a composite of blocked visual speech and distorted acoustics. Third, we could confirm previous findings, that the neural benefit of visual speech varies strongly across individuals. We show that this general individual ability predicts how much people engage in visual speech tracking in difficult AV listening situations. Interestingly, this was not correlated with hearing thresholds and therefore does seem to be a widely used compensatory strategy in the hearing impaired.

Chronically low NMNAT2 expression causes sub-lethal SARM1 activation and altered response to nicotinamide riboside in axons
Nicotinamide mononucleotide adenylyltransferase 2 (NMNAT2) is an endogenous axon survival factor that maintains axon health by blocking activation of the downstream pro-degenerative protein SARM1 (sterile alpha and TIR motif containing protein 1). While complete absence of NMNAT2 in mice results in extensive axon truncation and perinatal lethality, the removal of SARM1 completely rescues these phenotypes. Reduced levels of NMNAT2 can be compatible with life, however they compromise axon development and survival. Mice born expressing sub-heterozygous levels of NMNAT2 remain overtly normal into old age but develop axonal defects in vivo and in vitro as well as behavioural phenotypes. Therefore, it is important to examine the effects of constitutively low NMNAT2 expression on SARM1 activation and disease susceptibility. Here we demonstrate that chronically low NMNAT2 levels reduce prenatal viability in mice in a SARM1-dependent manner and lead to sub-lethal SARM1 activation in morphologically intact axons of superior cervical ganglion (SCG) primary cultures. This is characterised by a depletion in NAD(P) and compromised neurite outgrowth. We also show that chronically low NMNAT2 expression reverses the NAD-enhancing effect of nicotinamide riboside (NR) in axons in a SARM1-dependent manner. These data indicate that low NMNAT2 levels can trigger sub-lethal SARM1 activation which is detectable at the molecular level and could predispose to human axonal disorders.

Forelimb movements contribute to hindlimb cutaneous reflexes during locomotion in cats
During quadrupedal locomotion, central circuits interacting with somatosensory feedback coordinate forelimb and hindlimb movements. How this is achieved is not clear. To determine if forelimb movements modulate hindlimb cutaneous reflexes involved in responding to an external perturbation, we stimulated the superficial peroneal nerve in six intact cats during quadrupedal locomotion and during hindlimb-only locomotion (with forelimbs standing on stationary platform) and in two spinal-transected cats during hindlimb-only locomotion. We compared cutaneous reflexes evoked in six ipsilateral and four contralateral hindlimb muscles. Results showed similar occurrence and phase-dependent modulation of short-latency inhibitory and excitatory responses during quadrupedal and hindlimb-only locomotion in intact cats. However, the depth of modulation was reduced in the ipsilateral semitendinosus during hindlimb-only locomotion. Additionally, longer-latency responses occurred less frequently in extensor muscles bilaterally during hindlimb-only locomotion while short-latency inhibitory and longer-latency excitatory responses occurred more frequently in the ipsilateral and contralateral sartorius anterior, respectively. After spinal transection, short-latency inhibitory and excitatory responses were similar to both intact conditions, while mid- or longer-excitatory responses were reduced or abolished. Our results suggest that the absence of forelimb movements suppresses inputs from supraspinal structures and/or cervical cord that normally contribute to longer-latency reflex responses in hindlimb extensor muscles.

Towards an Eye-Brain-Computer Interface: Combining Gaze with the Stimulus-Preceding Negativity for Target Selections in XR
Gaze-assisted interaction techniques enable intuitive selections without requiring manual pointing but can result in unintended selections, known as Midas touch. A confirmation trigger eliminates this issue but requires additional physical and conscious user effort. Brain-computer interfaces (BCIs), particularly passive BCIs harnessing anticipatory potentials such as the Stimulus-Preceding Negativity (SPN) - evoked when users anticipate a forthcoming stimulus - present an effortless implicit solution for selection confirmation. Within a VR context, our research uniquely demonstrates that SPN has the potential to decode intent towards the visually focused target. We reinforce the scientific understanding of its mechanism by addressing a confounding factor - we demonstrate that the SPN is driven by the user's intent to select the target, not by the stimulus feedback itself. Furthermore, we examine the effect of familiarly placed targets, finding that SPN may be evoked quicker as users acclimatize to target locations; a key insight for everyday BCIs.

Increased perceptual reliability reduces membrane potential variability in cortical neurons
Uncertainty is omnipresent. While humans and other animals take uncertainty into account during decision making, it remains unclear how it is represented in cortex. To investigate the effect of stimulus reliability on uncertainty representation in cortical neurons, we analyzed single unit activity data recorded in mouse PPC, while animals performed a multisensory change detection task. We further used simulation-based inference (SBI) to infer membrane potential statistics underlying the spiking ac- tivity. Our analysis shows that stimulus changes increase spiking rate while decreasing its variability. The inferred membrane potential statistics suggest that PPC neurons decrease their membrane potential variability in response to task relevant stimuli. Furthermore, more perceptually reliable stimuli lead to a larger decrease in membrane potential variability than less reliable ones. These findings suggest that individual cortical neurons track uncertainty, providing Bayesian benefits for downstream computations.

Pre-stimulus alpha oscillations encode stimulus-specific visual predictions
Predictions of future events have a major impact on how we process sensory signals. However, it remains unclear how the brain keeps predictions online in anticipation of future inputs. Here, we combined magnetoencephalography (MEG) and multivariate decoding techniques to investigate the content of perceptual predictions and their frequency characteristics. Participants were engaged in a shape discrimination task, while auditory cues predicted which specific shape would likely appear. Frequency analysis revealed significant oscillatory fluctuations of predicted shape representations in the pre-stimulus window in the alpha band (10 - 11Hz). Furthermore, we found that this stimulus-specific alpha power was linked to expectation effects on shape discrimination. Our findings demonstrate that sensory predictions are embedded in pre-stimulus alpha oscillations and modulate subsequent perceptual performance, providing a neural mechanism through which the brain deploys perceptual predictions.

A genome-wide RNA interference screening reveals protectiveness of SNX5 knockdown in a Parkinson`s disease cell model
Background: Alpha-synuclein is a major player in the pathophysiology of a group of diseases called synucleinopathies, which include Parkinson`s disease, dementia with Lewy bodies, and multiple system atrophy. To date, there is no disease-modifying therapy available for these synucleinopathies. Furthermore, the intracellular mechanisms by which alpha-synuclein confers toxicity are not yet fully understood. Therefore, it is of utmost importance to investigate the pathophysiology of alpha-synuclein-induced toxicity in order to identify novel molecular targets for the development of disease-modifying therapies. Methods: In the present study, we performed the first genome-wide siRNA modifier screening in a human postmitotic neuronal cell model using alpha-synuclein-induced toxicity as read-out. In a multi-step approach, we identified several genes, whose knockdown protected from alpha-synuclein-induced toxicity. The main hit was further validated by different methods, including immunofluorescence microscopy, qPCR, and Western blot. Results: The highest protection was achieved by knockdown of SNX5, which encodes the SNX5 protein, a component of the retromer complex. We confirmed the protective efficacy of SNX5 knockdown with an independent siRNA system. SNX5 protein is part of SNX-BAR heterodimers, which are part of the retromer complex. We found that extracellular and overexpressed intracellular alpha-synuclein led to fragmentation of the trans-Golgi network, which was prevented by SNX5 knockdown by confining alpha-synuclein in early endosomes. Conclusion: In summary, our data suggest that SNX5 plays an important role in trafficking and toxicity of alpha-synuclein. Therefore, SNX5 appears to be a possible target for therapeutic interventions in synucleinopathies.

Distractor-response binding influences visual search
Intertrial priming effects in visual search and action control suggest the involvement of binding and retrieval processes. However, the role of distractor-response binding (DRB) in visual search has been largely overlooked, and the specific processing stage within the functional architecture of attentional guidance where the DRB occurs remains unclear. To address these gaps, we implemented two search tasks, where participants responded based on a separate feature from the one defining the target. We kept the target dimension consistent across trials while varying the color and shape of the distractor. Moreover, we either repeated or randomized the target position in different sessions. Our results revealed a pronounced response priming, a difference between trials where the response changed vs. repeated: they were stronger when distractor features or the target position were repeated than they varied. Furthermore, the distractor feature priming, a difference between the distractor features repetition and switch, was contingent on the target position, suggesting that DRB likely operates at late stages of target identification and response selection. These insights affirm the presence of DRB during visual search and support the framework of binding and retrieval in action control as a basis for observed intertrial priming effects related to distractor features.

Pavlovian cue-evoked alcohol seeking is disrupted by ventral pallidal inhibition
Cues paired with alcohol can be potent drivers of craving, alcohol-seeking, consumption, and relapse. While the ventral pallidum is implicated in appetitive and consummatory responses across several reward classes and types of behaviors, its role in behavioral responses to Pavlovian alcohol cues has not previously been established. Here, we tested the impact of optogenetic inhibition of ventral pallidum on Pavlovian-conditioned alcohol-seeking in male Long Evans rats. Rats underwent Pavlovian conditioning with an auditory cue predicting alcohol delivery to a reward port and a control cue predicting no alcohol delivery, until they consistently entered the reward port more during the alcohol cue than the control cue. We then tested the within-session effects of optogenetic inhibition during 50% of cue presentations. We found that optogenetic inhibition of ventral pallidum during the alcohol cue reduced port entry likelihood and time spent in the port, and increased port entry latency. Overall, these results suggest that normal ventral pallidum activity is necessary for Pavlovian alcohol-seeking.

Convergence of inputs from the basal ganglia with layer 5 of motor cortex and cerebellum in mouse motor thalamus
A key to motor control is the motor thalamus, where several inputs converge. One excitatory input originates from layer 5 of primary motor cortex (M1L5), while another arises from the deep cerebellar nuclei (Cb). M1L5> terminals distribute throughout the motor thalamus and overlap with GABAergic inputs from the basal ganglia output nuclei, the internal segment of the globus pallidus (GPi) and substantia nigra pars reticulata (SNr). In contrast, it is thought that Cb and basal ganglia inputs are segregated. Therefore, we hypothesized that one potential function of the GABAergic inputs from basal ganglia is to selectively inhibit, or gate, excitatory signals from M1L5 in the motor thalamus. Here, we tested this possibility and determined the circuit organization of mouse (both sexes) motor thalamus using an optogenetic strategy in acute slices. First, we demonstrated the presence of a feedforward transthalamic pathway from M1L5 through motor thalamus. Importantly, we discovered that GABAergic inputs from the GPi and SNr converge onto single motor thalamic cells with excitatory synapses from M1L5 and, unexpectedly, Cb as well. We interpret these results to indicate that a role of the basal ganglia is to gate the thalamic transmission of M1L5 and Cb information to cortex.

5-HT1B receptors mediate dopaminergic inhibition of vesicular fusion and GABA release from striatonigral synapses.
The substantia nigra pars reticulata (SNr), a crucial basal ganglia output nucleus, contains a dense expression of dopamine D1 receptors (D1Rs), along with dendrites belonging to dopaminergic neurons of substantia nigra pars compacta. These D1Rs are primarily located on the terminals of striatonigral medium spiny neurons, suggesting their involvement in the regulation of neurotransmitter release from the direct pathway in response to somatodendritic dopamine release. To explore the hypothesis that D1Rs modulate GABA release from striatonigral synapses, we conducted optical recordings of striatonigral activity and postsynaptic patch-clamp recordings from SNr neurons in the presence of dopamine and D1R agonists. We found that dopamine inhibits optogenetically triggered striatonigral GABA release by modulating vesicle fusion and Ca2+ influx in striatonigral boutons. Notably, the effect of DA was independent of D1R activity but required activation of 5-HT1B receptors. Our results suggest a serotonergic mechanism involved in the therapeutic actions of dopaminergic medications for Parkinson's disease and psychostimulant-related disorders.

Association of microglia loss with hippocampal network impairments as a turning point in the amyloid pathology progression.
Alzheimers disease (AD) is a progressive neurological disorder causing memory loss and cognitive decline. The underlying causes of cognitive deterioration and neurodegeneration remain unclear, leading to a lack of effective strategies to prevent dementia. Recent evidence highlights the role of neuroinflammation, particularly involving microglia, in AD onset and progression. Characterizing the initial phase of AD can lead to the discovery of new biomarkers and therapeutic targets, facilitating timely interventions for effective treatments. We used the AppNL-G-F knock-in mouse model, which resembles the amyloid pathology and neuroinflammatory characteristics of AD, to investigate the transition from a pre-plaque to an early plaque stage with a combined functional and molecular approach. Our experiments show a progressive decrease in the power of cognition-relevant hippocampal gamma oscillations during the early stage of amyloid pathology, together with a modification of fast-spiking interneuron intrinsic properties and postsynaptic input. Consistently, transcriptomic analyses revealed that these effects are accompanied by changes in synaptic function-associated pathways. Concurrently, homeostasis- and inflammatory-related microglia signature genes were downregulated. Moreover, we found a decrease in Iba1-positive microglia in the hippocampus that correlates with plaque aggregation and neuronal dysfunction. Collectively, these findings support the hypothesis that microglia play a protective role during the early stages of amyloid pathology by preventing plaque aggregation, supporting neuronal homeostasis, and overall preserving the functionality of the oscillatory network. These results suggest that the early loss of microglia could be a pivotal event in the progression of AD, potentially triggering plaque deposition, impairment of fast-spiking interneurons, and the breakdown of the oscillatory circuitry in the hippocampus.

Bayesian semantic surprise based on different types of regularities predicts the N400 and P600 brain signals
The brain's remarkable ability to extract patterns from sequences of events has been demonstrated across cognitive domains and is a central assumption of predictive processing theories. While predictions shape language processing at the level of meaning, little is known about the underlying learning mechanism. Here, we investigated how continuous statistical inference in a semantic sequence influences the neural response. 60 participants were presented with a semantic oddball-like roving paradigm, consisting of sequences of nouns from different semantic categories. Unknown to the participants, the overall sequence contained an additional manipulation of transition probability between categories. Two Bayesian sequential learner models that captured different aspects of probabilistic learning were used to derive theoretical surprise levels for each trial and investigate online probabilistic semantic learning. The N400 ERP component was primarily modulated by increased probability with repeated exposure to the categories throughout the experiment, which essentially represents repetition suppression. This N400 repetition suppression likely prevented sizeable influences of more complex predictions such as those based on transition probability, as any incoming information was already continuously active in semantic memory. In contrast, the P600 was associated with semantic surprise in a transition probability model over recent observations, possibly indicating a working memory update in response to violations of these conditional dependencies. The results support probabilistic predictive processing of semantic information and demonstrate that continuous update of distinct statistics differentially influences language related ERPs.

PRMT5 is required for full-length HTT expression by repressing multiple proximal intronic polyadenylation sites
Expansion of the CAG trinucleotide repeat tract in exon 1 of the Huntingtin (HTT) gene above a threshold of ~36 repeats causes Huntington's disease (HD) through the expression of a polyglutamine-expanded form of the HTT protein. This mutation triggers wide-ranging cellular and biochemical pathologies leading to cognitive, motor, and psychiatric symptoms in HD patients. As accurate splicing is required to produce the full-length HTT protein of 348 kDa, targeting HTT splicing with small molecule drugs is a compelling approach to lower HTT protein levels to treat HD, and splice modulators are being tested in the clinic. Here, we identify PRMT5 as a novel regulator of HTT mRNA splicing and alternative polyadenylation. PRMT5 inhibition disrupts the splicing of HTT introns 9 and 10, leading to activation of multiple proximal intronic polyadenylation sites within these introns and promoting premature termination, cleavage and polyadenylation (PCPA) of the HTT mRNA, thus lowering total HTT protein levels. We also detected increasing levels of these truncated, intron-containing HTT transcripts across a series of neuronal differentiation samples which correlated with lower PRMT5 expression. Notably, PRMT5 inhibition in glioblastoma (GBM) stem cells potently induced neuronal differentiation. We posit that PRMT5-mediated regulation of intronic polyadenylation, premature termination and cleavage of the HTT mRNA modulates HTT expression and plays an important role during embryonic development and neuronal differentiation.

Amyloid Beta Oligomers Accelerate ATP-Dependent Phase Separation of Ago2 to RNA Processing Bodies
miRNA-repressed mRNAs and Ago proteins are known to be localized to RNA-processing bodies, the subcellular structures which are formed due to assembly of several RNA binding and regulatory proteins in eukaryotic cells. Ago2 is the most important miRNA binding protein that by forming complex with miRNA binds to mRNAs having cognate miRNA binding sites and represses protein synthesis in mammalian cells. Factors which control compartmentalization of Ago2 and miRNA-repressed mRNAs to RNA processing bodies are largely unknown. We have adopted a detergent permeabilized cell-based assay system to follow the phase separation of exogenously added Ago2 to RNA processing bodies in vitro. The Ago2 phase separation process is ATP dependent and is influenced by osmolarity and salt concentration of the reaction buffer. miRNA binding of Ago2 is essential for its targeting to RNA processing bodies and the compartmentalization process gets retarded by miRNA binding "sponge" protein HuR. This assay system found to be useful in identification of amyloid beta oligomers as miRNA-activity modulators which repress miRNA activity by enhancing Ago2-miRNP targeting to RNA processing bodies.

PEACOC - Detecting and classifying a wide range of epileptiform activity patterns in rodents
Epileptiform activity (EA) manifests in diverse patterns of hypersynchronous network activity. Fundamental research mostly addresses two extreme patterns, individual epileptiform spikes and seizures. We developed PEACOC to detect and classify a wide range of EA patterns in local field potentials. PEACOC delimits EA patterns as bursts of epileptiform spikes, and classifies these bursts according to spike load. In EA from kainate-injected mice, burst patterns displayed a continuum of spike loads. With PEACOC, we partitioned this continuum into bursts of high, medium and low spike load. High-load bursts resembled electrographic seizures. The EA patterns automatically retrieved by PEACOC were reproducible and comparable across animals and laboratories. PEACOC has been employed to diagnose the overall burden of EA in individual mice, and to describe epileptic dynamics at multiple time-scales. We here further report that the rate of high-load bursts was anti-correlated to granule cell dispersion in the dentate gyrus.

Astrocyte CCN1 stabilizes neural circuits in the adult brain
Neural circuits in many brain regions are refined by experience. Sensory circuits support higher plasticity at younger ages during critical periods - times of circuit refinement and maturation - and limit plasticity in adulthood for circuit stability. The mechanisms underlying these differing plasticity levels and how they serve to maintain and stabilize the properties of sensory circuits remain largely unclear. By combining a transcriptomic approach with ex vivo electrophysiology and in vivo imaging techniques, we identify that astrocytes release cellular communication network factor 1 (CCN1) to maintain synapse and circuit stability in the visual cortex. By overexpressing CCN1 in critical period astrocytes, we find that it promotes the maturation of inhibitory circuits and limits ocular dominance plasticity. Conversely, by knocking out astrocyte CCN1 in adults, binocular circuits are destabilized. These studies establish CCN1 as a novel astrocyte-secreted factor that stabilizes neuronal circuits. Moreover, they demonstrate that the composition and properties of sensory circuits require ongoing maintenance in adulthood, and that these maintenance cues are provided by astrocytes.

Perceptual awareness of near-threshold tones scales gradually with auditory cortex activity and pupil dilation
Perceptual awareness covaries with negative-going responses in sensory cortex, but the derived concept of perceptual awareness negativity has been criticized a.o. because of its presence for undetected stimuli. To evaluate this objection, we combined magnetoencephalography, electroencephalography, and pupillometry to study the roles of sustained attention and response criterion on the auditory awareness negativity. Participants first detected distractor sounds and denied hearing task-irrelevant near-threshold tones, which evoked neither awareness negativity nor pupil dilation. These same tones evoked responses when task-relevant, stronger for hit but also present for miss trials. To explore if response criterion could explain the presence of responses for miss trials, participants rated their perception on a six-point scale. Decreasing perception ratings were associated with gradually reduced evoked responses, consistent with signal detection theory. These results support the concept of an awareness negativity that is modulated by attention, but does not exhibit a non-linear threshold mechanism.

Highly conserved brain vascular receptor ALPL mediates transport of engineered viral vectors across the blood-brain barrier
Delivery of systemically administered therapeutics to the central nervous system (CNS) is restricted by the blood-brain barrier (BBB). Bioengineered Adeno-Associated Virus (AAV) capsids have been shown to penetrate the BBB with great efficacy in mouse and non-human primate models, but their translational potential is often limited by species selectivity and undefined mechanisms of action. Here, we apply our RNA-guided TRACER AAV capsid evolution platform to generate VCAP-102, an AAV9 variant with markedly increased brain tropism following intravenous delivery in both rodents and primates. VCAP-102 demonstrates a similar CNS tropism in cynomolgus macaque, african green monkey, marmoset and mouse, showing 20- to 400-fold increased transgene expression across multiple brain regions relative to AAV9. We demonstrate that the enhanced CNS tropism of VCAP-102 results from direct interaction with alkaline phosphatase (ALPL), a highly conserved membrane-associated protein expressed on the brain vasculature. VCAP-102 interacts with human, primate and murine ALPL isoforms, and ectopic expression of ALPL is sufficient to initiate receptor-mediated transcytosis of VCAP-102 in an in vitro transwell model. Our work identifies VCAP-102 as a cross-species CNS gene delivery vector with a strong potential for clinical translation and establishes ALPL as a brain delivery shuttle capable of efficient BBB transport to maximize CNS delivery of biotherapeutics.

Distributed encoding of hippocampal information in mossy cells
In neural information processing, the nervous system transmits neuronal activity across layers of neural circuits, occasionally passing through small layers composed only of sparse neurons. Hippocampal hilar mossy cells (MCs) constitute such a typical bottleneck layer. In vivo/vitro patch-clamp recordings revealed that MCs were reliably depolarized in response to sharp-wave ripples (SWRs), synchronous neuronal events transmitted from the CA3 region to the dentate gyrus via the MC layer. Machine-learning algorithms predicted the waveforms of SWRs in the CA3 region, based on the MC depolarization waveforms, suggesting that CA3 neural information is indeed transmitted to the MC layer. However, the prediction accuracy varied; i.e., a particular MC showed a more robust association with a particular SWR cluster, and the SWR cluster associated with one MC rarely overlapped with the SWR clusters associated with other MCs. Thus, CA3 network activity is distributed across MC ensembles with pseudo-orthogonal neural representations, allowing the small MC layer to effectively compress hippocampal information.

Exploring working memory updating processes of the human subcortex using 7T MRI
The prefrontal-cortex basal ganglia working memory (PBWM) model (Hazy et al., 2007; O'Reilly & Frank, 2006) proposes that working memory representations are updated via a striatal gating mechanism but lacks conclusive empirical support for the postulated subcortical involvement. A growing body of research suggests that dopamine is also involved in working memory updating (Braver & Cohen, 2000; Cools & D'Esposito, 2011; D'Ardenne et al., 2012; Jongkees, 2020). In this study, we investigated subcortical -in particular, possible dopaminergic- involvement in working memory updating subprocesses using the reference-back task and ultra-high field 7 Tesla fMRI. Using a scanning protocol optimized for BOLD-sensitivity in the subcortex, we found no evidence of subcortical activation during working memory gate opening, which challenges the PBWM model's striatal gating mechanism. However, during gate closing, subcortical activation was observed. Furthermore, a ready-to-update mode demonstrated large-spread subcortical activation, including basal ganglia nuclei, suggesting that the basal ganglia are engaged in general updating processes rather than specifically controlling the working memory gate. Evidence for activity in dopaminergic midbrain regions was also observed in both contrasts. Also, substituting new information into working memory elicited activation in dopamine-producing midbrain regions along with the striatum, thalamus, and prefrontal cortex, indicating engagement of the basal ganglia-thalamo-cortical loop possibly driven by dopaminergic activity. These findings expand our understanding of subcortical regions involved in working memory updating, providing additional insights into the role of the dopaminergic midbrain.

Information is asymmetry: spatial relations were encoded by asymmetric mnemonic manifolds
Substantial evidence suggests that working memory (WM) leverages relational representations to provide flexible support for cognitive functions, a capacity likely derived from the dynamic nature of neural codes in WM. However, how these dynamic codes represent and maintain relations remains unclear. Here, we examined the transformation of neural geometries in the dorsal prefrontal cortex of monkeys performing a visuospatial delayed-match/nonmatch task, where the monkeys were instructed to hold the spatial location of a white square in WM to match it with the spatial location of a subsequent square. We found that the sensory manifold during the square's presence and the mnemonic manifold after the square's offset both aligned with the stimulus manifold. However, significant differences emerged between the sensory and mnemonic manifolds, exhibiting little correlation in their neural geometries. Further analysis on the dynamic transformation from the sensory to mnemonic manifold revealed a process of expansion followed by flattening: the asymmetric sensory manifold first expanded into a symmetric neural geometry immediately after the square's onset offset, which then gradually flattened along dimensions different from those initially expanded, culminating in an asymmetric mnemonic manifold. This dynamic process of reconstruction not only remained its faithfulness to the stimulus geometry but also gained the flexibility to meet task demands. In sum, this transformation from asymmetry to symmetry and back to asymmetry in neural geometry precisely illustrates the dynamics of memory reconstruction, shedding lights on the subjective nature of WM that generates both accurate and illusory representation of the world we lived in.

Early life stress-induced miR-708-5p affects bipolar disorder-associated phenotypes through neuronatin downregulation
The underlying physiological and molecular mechanisms of bipolar disorder (BD) remain largely unknown. Here, by using unbiased small RNA sequencing in peripheral blood mononuclear cells (PBMCs), we found that miR-708-5p, a microRNA that was previously associated with BD, is the most strongly upregulated microRNA in peripheral blood of both healthy human subjects with a high genetic or environmental predisposition to develop mood disorders (MDs). Furthermore, miR-708-5p is strongly upregulated in patients diagnosed with BD and has potential in conjunction with the previously identified miR-499-5p to differentiate BD patients from patients suffering from major depressive disorder (MDD) and healthy controls. miR-708 is also upregulated in the hippocampus of wild type juvenile rats that underwent social isolation, as well as in juvenile rats heterozygous for the BD risk gene Cacna1c. Furthermore, ectopic overexpression of miR-708-5p in the hippocampus of adult male mice leads to BD-associated endophenotypes, such as reduced behavioral despair, enhanced compulsivity, and short-term memory impairments. miR-708-5p directly targets Neuronatin (Nnat), an endoplasmic reticulum (ER) resident protein involved in calcium homeostasis. Restoring Nnat expression in the hippocampus of miR-708-5p overexpressing mice rescues BD-associated endophenotypes. In summary, we functionally link miR-708-5p dependent regulation of Nnat to BD, with potential implications for BD diagnosis and therapy.