bioRxiv Subject Collection: Neuroscience's Journal

Brain-wide impacts of sedation on spontaneous activity and auditory processing in larval zebrafish
Despite their widespread use, we have limited knowledge of the mechanisms by which sedatives mediate their effects on brain-wide networks. This is, in part, due to the technical challenge of observing activity across large populations of neurons in normal and sedated brains. In this study, we examined the effects of the sedative dexmedetomidine, and its antagonist atipamezole, on spontaneous brain dynamics and auditory processing in zebrafish larvae. Our brain-wide, cellular-resolution calcium imaging reveals, for the first time, the brain regions involved in these network-scale dynamics and the individual neurons that are affected within those regions. Further analysis reveals a variety of dynamic changes in the brain at baseline, including marked reductions in spontaneous activity, correlation, and variance. The reductions in activity and variance represent a 'quieter' brain state during sedation, an effect that causes highly correlated evoked activity in the auditory system to stand out more than it does in un-sedated brains. We also observe a reduction in auditory response latencies across the brain during sedation, suggesting that the removal of spontaneous activity leaves the core auditory pathway free of impingement from other non-auditory information. Finally, we describe a less dynamic brain-wide network during sedation, with a higher energy barrier and a lower probability of brain state transitions during sedation. In total, our brain-wide, cellular-resolution analysis shows that sedation leads to quieter, more stable, and less dynamic brain, and that against this background, responses across the auditory processing pathway become sharper and more prominent.

Distributed fMRI dynamics predict distinct EEG rhythms across sleep and wakefulness
The brain exhibits rich oscillatory dynamics that vary across tasks and states, such as the EEG oscillations that define sleep. These oscillations play critical roles in cognition and arousal, but the brainwide mechanisms underlying them are not yet described. Using simultaneous EEG and fast fMRI in subjects drifting between sleep and wakefulness, we developed a machine learning approach to investigate which brainwide fMRI dynamics predict alpha (8-12 Hz) and delta (1-4 Hz) rhythms. We predicted moment-by-moment EEG power from fMRI activity in held-out subjects, and found that information about alpha power was represented by a remarkably small set of regions, segregated in two distinct networks linked to arousal and visual systems. Conversely, delta rhythms were diffusely represented on a large spatial scale across the cortex. These results identify distributed networks that predict delta and alpha rhythms, and establish a computational framework for investigating fMRI brainwide dynamics underlying EEG oscillations.

Identifying the function of the NMDA NR1C2 subunit through its interaction with Magi-2 during inflammatory pain
Much is understood about the structure and gating properties of NMDA receptors (NMDAR), but the function of the carboxy-terminal splice variant of the NR1 subunit, NR1C2 has never been identified. By studying the scaffolding protein Magi-2 in animal models of inflammatory pain, we discovered how NR1C2 protein is specifically regulated. We found that Magi-2 deficiency resulted in decreased pain behavior and a concomitant reduction in NR1C2 protein. Magi-2 contains WW domains, domains typically found in ubiquitin ligases. We identified an atypical WW-binding domain within NR1C2 which conferred susceptibility to Nedd4-1 ubiquitin-ligase dependent degradation. We used lipidated peptidomimetics derived from the NR1C2 sequence and found that NR1C2 protein levels and pain behavior can be pharmacologically targeted. The function of NR1C2 is to give lability to a pool of NMDAR, important for pain signaling.

Stimulating the medial prefrontal cortex disrupts inhibitory control over memory by modulating frontal and parietal brain regions
The act of recalling memories can paradoxically lead to the forgetting of other associated memories, a phenomenon known as retrieval-induced forgetting (RIF). This effect is thought to be mediated by inhibitory control mechanisms in the prefrontal cortex of the brain. Here we investigated whether stimulation of the medial prefrontal cortex (mPFC) with transcranial direct current stimulation modulates inhibitory control during memory retrieval in a RIF paradigm. In a randomized study, fifty participants received either real or sham stimulation, before performing retrieval practice on target memories. After retrieval practice, a final test was administered to measure the impact of stimulation on RIF. We found that stimulation selectively increased the retrieval accuracy of non-target memories and thus decreased RIF, suggesting a disruption of inhibitory control. Meanwhile, no change arose for the retrieval accuracy of target memories. The reduction in RIF was caused by a more pronounced beta desynchronization within the left dorsolateral prefrontal cortex (left-DLPFC), in an early time window (<500 msec) after the onset of the cue during retrieval practice. This, in turn, led to a stronger beta desynchronization within the parietal cortex in a later time window, an established marker for successful memory retrieval. Together, our results establish the causal involvement of the mPFC in actively suppressing competing memories and we demonstrate that while forgetting arises as a consequence of retrieving specific memories, these two processes are functionally independent. Finally, we demonstrate that beta desynchronization in the fronto-parietal brain regions indicates the disruption of inhibitory control.

Endocannabinoid-mediated rescue of somatosensory cortex activity, plasticity and related behaviors following an early in life concussion.
Due to the assumed plasticity of immature brain, early in life brain alterations are thought to lead to better recoveries in comparison to the mature brain. Despite clinical needs, how neuronal networks and associated behaviors are affected by early in life brain stresses, such as pediatric concussions, have been overlooked. Here we provide first evidence in mice that a single early in life concussion durably increases neuronal activity in the somatosensory cortex into adulthood, disrupting neuronal integration while the animal is performing sensory-related tasks. This represents a previously unappreciated clinically relevant mechanism for the impairment of sensory-related behavior performance. Furthermore, we demonstrate that pharmacological modulation of the endocannabinoid system a year post-concussion is well-suited to rescue neuronal activity and plasticity, and to normalize sensory-related behavioral performance, addressing the fundamental question of whether a treatment is still possible once post-concussive symptoms have developed, a time-window compatible with clinical treatment.

Event-Related Potential Markers of Subject Cognitive Decline and Mild Cognitive Impairment during a sustained visuo-attentive task
INTRODUCTION. Subjective cognitive decline (SCD), mild cognitive impairment (MCI), or severe Alzheimer's disease stages are still lacking clear electrophysiological correlates. METHODS. In 145 subjects (86 SCD, 40 MCI, and 19 healthy subjects (HS)), we analysed event-related potentials observed during a sustained visual attention task, aiming to distinguish biomarkers associated with group conditions and performance. RESULTS. We observed distinct patterns among group conditions in the occipital P1 and N1 components during the stimulus encoding phase, as well as in the central P3 component during the stimulus decision phase. The order of ERP components was non-monotonic, indicating a closer resemblance between MCI and HS. ERP features from occipital channels exhibited greater differences between SCD and MCI. Task performance was significantly enhanced in the central channels during the decision phase. DISCUSSION. Those results support evidence of early stage, neural anomalies linked to visuo-attentive alterations in cognitive decline as candidate EEG biomarkers.

The sense of agency from active causal inference
This study investigates the active component of the sense of agency (SoA) which is often overlooked in the literature, and posits that SoA is fundamentally an outcome of active causal inference regarding one's own actions and their impact on the environment. Participants engaged in tasks requiring control over visual objects via a computer mouse, with tasks designed to test their ability to judge control or detect controlled objects under varying noise conditions. Our findings reveal that participants actively formed high-level, low-dimensional action policies (plans) that were idiosyncratic across but consistent within individuals to effectively infer their degree of control in a noisy environment. Employing transformer-LSTM-based autoencoders, we captured these low-dimensional action plans and demonstrated that the geometrical and dynamical properties of these action plans could predict behavioural profiles in the tasks with remarkable accuracy. This suggests that participants' sense of control is shaped by actively altering action plans, viewed as generating causal evidence through intervention. Further, participants proactively expanded the diversity of their action plans, as measured by the dimensionality of the action plan distribution. It facilitates the exploration of the available action plan options while concurrently accumulating causal evidence for the inference process. Contrarily, patients with schizophrenia exhibited reduced action plan diversity, suggesting limited active control inference and impaired detection of self-relevant cues. Yet, their judgment responses closely matched predictions from the geometrical and dynamical aspects of their action plans, indicating that they adapt a proper decision boundary to optimise their active inference about their causal role in environmental changes. In conclusion, these findings expand our knowledge, offering a more comprehensive understanding of the sense of agency, deeply rooted in the process of active causal inference.

A spinal cord injury time and severity consensus transcriptomic reference suite in rat reveals translationally-relevant biomarker genes
Spinal cord injury (SCI) is a devastating condition that leads to motor, sensory, and autonomic dysfunction. Current therapeutic options remain limited, emphasizing the need for a comprehensive understanding of the underlying SCI-associated molecular mechanisms. This study characterized distinct SCI phases and severities at the gene and functional levels, focusing on biomarker gene identification. Our approach involved a systematic review, individual transcriptomic analysis, gene meta-analysis, and functional characterization. We compiled a total of fourteen studies with 273 samples, leading to the identification of severity-specific biomarker genes for injury prognosis (e.g., Srpx2, Hoxb8, Acap1, Snai1, and Aadat) and phase-specific genes for the precise classification of the injury profile (e.g., Il6, Fosl1, Cfp, C1qc, Cp). We investigated the potential transferability of severity-associated biomarkers and identified a twelve-gene signature that predicted injury prognosis from human blood samples. We also report the development of MetaSCI-app - an interactive web application designed for researchers - that allows the exploration and visualization of all generated results (https://metasci-cbl.shinyapps.io/metaSCI). Overall, we present a transcriptomic reference and provide a comprehensive framework for assessing SCI considering severity and time perspectives.

Systemic inflammation triggers long-lasting neuroinflammation and accelerates neurodegeneration in a rat model of Parkinson's disease overexpressing human alpha-synuclein
Increasing efforts have been made to elucidate how genetic and environmental factors interact in Parkinson's disease (PD). In the present study, we assessed the development of PD-like symptoms on a genetic PD rat model overexpressing human -synuclein (Snca+/+) at a presymptomatic age, exposed to a pro-inflammatory insult by intraperitoneal injection of lipopolysaccharide (LPS), using immunohistology, high-dimensional flow cytometry, electrophysiology, and behavioral analyses. A single injection of LPS to both WT and Snca+/+ rats triggered long-lasting increased activation of pro-inflammatory microglial markers, infiltrating monocytes and T-lymphocytes. However, only LPS Snca+/+ rats displayed dopaminergic neuronal loss in the substantia nigra pars compacta (SNpc), associated with a reduction of evoked dopamine release in the striatum. No significant changes were observed in the behavioral domain. We propose our double-hit animal as a reliable model to investigate the mechanisms whereby -synuclein and inflammation interact to promote neurodegeneration in PD.

PREFRONTAL CORRELATES OF FEAR GENERALIZATION DURING ENDOCANNABINOID DEPLETION
Maladaptive fear generalization is one of the hallmarks of trauma-related disorders. The endocannabinoid 2-arachidonoylglycerol (2-AG) is crucial for modulating anxiety, fear, and stress adaptation but its role in balancing fear discrimination versus generalization is not known. To address this, we used a combination of plasma endocannabinoid measurement and neuroimaging from a childhood maltreatment exposed and non-exposed mixed population combined with human and rodent fear conditioning models. Here we show that 2-AG levels are inversely associated with fear generalization at the behavioral level in both mice and humans. In mice, 2-AG depletion increases the proportion of neurons, and the similarity between neuronal representations, of threat-predictive and neutral stimuli within prelimbic prefrontal cortex ensembles. In humans, increased dorsolateral prefrontal cortical-amygdala resting state connectivity is inversely correlated with fear generalization. These data provide convergent cross-species evidence that 2-AG is a key regulator of fear generalization and suggest 2-AG deficiency could represent a trauma-related disorder susceptibility endophenotype.

Supervised deep machine learning models predict forelimb movement from excitatory neuronal ensembles and suggest distinct pattern of activity in CFA and RFA networks
Neuronal networks in the motor cortex are crucial for driving complex movements. Yet it remains unclear whether distinct neuronal populations in motor cortical subregions encode complex movements. Using in vivo two-photon calcium imaging (2P) on head-fixed grid-walking animals, we tracked the activity of excitatory neuronal networks in layer 2/3 of caudal forelimb area (CFA) and rostral forelimb area (RFA) in motor cortex. Employing supervised deep machine learning models, a support vector machine (SVM) and feed forward deep neural networks (FFDNN), we were able to decode the complex grid-walking movement at the level of excitatory neuronal ensembles. This study indicates significant differences between RFA and CFA decoding accuracy in both models. Our data demonstrate distinct temporal-delay decoding patterns for movements in CFA and RFA, as well as a selective ensemble of movement responsive neurons with higher distribution in CFA, suggesting specific patterns of activity-induced movement in these two networks.

Examining motor evidence for the pause-then-cancel model of action-stopping: Insights from motor system physiology
Stopping initiated actions is fundamental to adaptive behavior. Longstanding, single-process accounts of action-stopping have been challenged by recent, two-process, 'pause-then-cancel' models. These models propose that action-stopping involves two inhibitory processes: 1) a fast Pause process, which broadly suppresses the motor system as the result of detecting any salient event, and 2) a slower Cancel process, which involves motor suppression specific to the cancelled action. A purported signature of the Pause process is global suppression, or the reduced corticospinal excitability (CSE) of task-unrelated effectors early on in action-stopping. However, unlike the Pause process, few (if any) motor system signatures of a Cancel process have been identified. Here, we used single- and paired-pulse TMS methods to comprehensively measure the local physiological excitation and inhibition of both responding and task-unrelated motor effector systems during action-stopping. Specifically, we measured CSE, short-interval intracortical inhibition (SICI), and the duration of the cortical silent period (CSP). Consistent with key predictions from the pause-then-cancel model, CSE measurements at the responding effector indicated that additional suppression was necessary to counteract Go-related increases in CSE during-action-stopping, particularly at later timepoints. Increases in SICI on Stop-signal trials did not differ across responding and non-responding effectors, or across timepoints. This suggests SICI as a potential source of global suppression. Increases in CSP duration on Stop-signal trials were more prominent at later timepoints. SICI and CSP duration therefore appeared most consistent with the Pause and Cancel processes, respectively. Our study provides further evidence from motor system physiology that multiple inhibitory processes influence action-stopping.

Slow running benefits: Boosts in mood and facilitation of prefrontal cognition even at very light intensity
Although running upright has been reported to have positive effects on both physical and mental health, the minimum running intensity/speed that would benefit mood and prefrontal cognition is not yet clear. For this reason, we aimed to investigate the acute effect of very slow running, which is classified as a very light intensity exercise, on mood, executive function (EF), and their neural substrates in the prefrontal cortex (PFC). Twenty-four healthy participants completed a 10-minute very slow running session on a treadmill at 35% [V]o2peak and a resting control session in randomized order. EF was measured using the Stroop task and the mood state was measured using the Two-Dimensional Mood Scale (TDMS) before and after both sessions. Cortical hemodynamic changes while performing the task were monitored using functional near-infrared spectroscopy (fNIRS). The results show that ten minutes of very slow running significantly enhanced mood, reduced Stroop interference time (i.e., enhanced EF), and elicited left lateral PFC activation. Moreover, head acceleration, the magnitude of up-and-down oscillations, was measured during running, and a significant positive correlation with pleasant mood was found. Head acceleration is a remarkable characteristic of running and may be one of the factors related to a pleasant mood induced by very slow running. In conclusion, the current study reveals that a single bout of running, even at very slow speed, elicits a pleasant mood and improved executive function with enhancing activation in prefrontal subregions. This shed light on the slow running benefits to brain health.

The Primate Cortical LFP Exhibits Multiple Spectral and Temporal Gradients and Widespread Task-Dependence During Visual Short-Term Memory
Although cognitive functions are hypothesized to be mediated by synchronous neuronal interactions in multiple frequency bands among widely distributed cortical areas, we still lack a basic understanding of the distribution and task dependence of oscillatory activity across the cortical map. Here, we ask how the spectral and temporal properties of the local field potential (LFP) vary across the primate cerebral cortex, and how they are modulated during visual short-term memory. We measured the LFP from 55 cortical areas in two macaque monkeys while they performed a visual delayed match to sample task. Analysis of peak frequencies in the LFP power spectra reveals multiple discrete frequency bands between 3-80 Hz that differ between the two monkeys. The LFP power in each band, as well as the Sample Entropy, a measure of signal complexity, display distinct spatial gradients across the cortex, some of which correlate with reported spine counts in layer 3 pyramidal neurons. Cortical areas can be robustly decoded using a small number of spectral and temporal parameters, and significant task dependent increases and decreases in spectral power occur in all cortical areas. These findings reveal pronounced, widespread and spatially organized gradients in the spectral and temporal activity of cortical areas. Task-dependent changes in cortical activity are globally distributed, even for a simple cognitive task.

The human claustrum tracks slow waves during sleep
Slow waves are a distinguishing feature of non-rapid-eye-movement (NREM) sleep, an evolutionarily conserved process critical for brain function. Non-human studies posit that the claustrum, a small subcortical nucleus, coordinates slow waves. We recorded claustrum neurons in humans during sleep. In contrast to neurons from other brain regions, claustrum neurons increased their activity and tracked slow waves during NREM sleep suggesting that the claustrum plays a role in human sleep architecture.

Evaluation of behavioral and neurochemical changes induced by carbofuran in zebrafish (Danio rerio)
Carbofuran (CF) is a carbamate class pesticide, widely used in agriculture for pest control in crops. On the other hand, CF is also detected as a contaminant in food and water sources. This pesticide has high toxicity in non-target organisms, and its presence in the environment poses a threat to the ecosystem. Research has revealed that this pesticide acts as an inhibitor of acetylcholinesterase (AChE), inducing an accumulation of acetylcholine in the brain. Consequently, this leads to the emergence of a cholinergic syndrome and various detrimental effects on human health. Nonetheless, our understanding of CF impact on the central nervous system remains elusive. Therefore, this study aimed to investigate the effects of CF on behavioral and neurochemical parameters in adult zebrafish. The animals were exposed for 96 hours to different concentrations of CF (5, 50, and 500 g/L) and subjected to behavioral assessments in the novel tank test (NTT) and social preference test (SPT). Subsequently, they were euthanized, and their brains were used to evaluate neurochemical markers associated with oxidative stress and AChE levels. In the NTT and SPT, CF did not alter the evaluated behavioral parameters. Furthermore, CF did not affect the levels of AChE, non-protein sulfhydryl groups, and thiobarbituric acid reactive species in the zebrafish brain. However, further research is needed regarding the environmental exposure of this compound to non-target organisms.

Acute sleep deprivation reduces fear memories in male and female mice
Sleep problems are a prominent feature of mental health conditions including post-traumatic stress disorder (PTSD). Despite its potential importance, the role of sleep in the development of and/or recovery from trauma-related illnesses is not understood. Interestingly, there are reports that sleep deprivation immediately after a traumatic experience can reduce fear memories, an effect that could be utilized therapeutically in humans. While the mechanisms of this effect are not completely understood, one possible explanation for these findings is that immediate sleep deprivation interferes with consolidation of fear memories, rendering them weaker and more sensitive to intervention. Here, we allowed fear-conditioned mice to sleep immediately after fear conditioning during a time frame (18 hr) that includes and extends beyond periods typically associated with memory consolidation before subjecting them to 6 hr of sleep deprivation. Mice deprived of sleep with this delayed regimen showed dramatic reductions in fear during tests conducted immediately after sleep deprivation, as well as 24 hr later. This sleep deprivation regimen also increased levels of mRNA encoding brain-derived neurotrophic factor (BDNF), a molecule implicated in neuroplasticity, in the basolateral amygdala (BLA), a brain area implicated in fear and its extinction. These findings raise the possibility that the effects of our delayed sleep deprivation regimen are not due to disruption of memory consolidation, but instead are caused by BDNF-mediated neuroadaptations within the BLA that actively suppress expression of fear. Treatments that safely reduce expression of fear memories would have considerable therapeutic potential in the treatment of conditions triggered by trauma.

Revealing brain network dynamics during the emotional state of suspense using topological data analysis
Suspense is an affective state ubiquitous in human life, from art to quotidian events. However, little is known about the behavior of large-scale brain networks during suspenseful experiences. To address this question, we examined the continuous brain responses of participants watching a suspenseful movie, along with reported levels of suspense from an independent set of viewers. We employ sliding window analysis and Pearson correlation to measure functional connectivity states over time. Then, we use Mapper, a topological data analysis tool, to obtain a graphical representation that captures the dynamical transitions of the brain across states; this representation enables the anchoring of the topological characteristics of the combinatorial object with the measured suspense. Our analysis revealed changes in functional connectivity within and between the salience, fronto-parietal, and default networks associated with suspense. In particular, the functional connectivity between the salience and fronto-parietal networks increased with the level of suspense. In contrast, the connections of both networks with the default network decreased. Together, our findings reveal specific dynamical changes in functional connectivity at the network level associated with variation in suspense, and suggest topological data analysis as a potentially powerful tool for studying dynamic brain networks.

Identifying a Distractor Produces Object-Based Inhibition in an Allocentric Reference Frame for Saccade Planning
We investigated whether distractor inhibition occurs relative to the target or fixation in a perceptual decision-making task using a purely saccadic response. During the process of discriminating a target from distractor, saccades made to a target deviate towards the distractor. Once discriminated, the distractor is inhibited, and trajectories deviate away from the distractor. Saccade deviation magnitudes provide a sensitive measure of target-distractor competition dependent on the distance between them. While saccades are planned in an egocentric reference frame (locations represented relative to fixation), object-based inhibition has been shown to occur in an allocentric reference frame (objects represented relative to each other independent of fixation). By varying the egocentric and allocentric distances of the target and distractor, we found that only egocentric distances contributed to saccade trajectories shifts towards the distractor during active decision-making. When the perceptual decision-making process was complete, and the distractor was inhibited, both ego- and allocentric distances independently contributed to saccade trajectory shifts away from the distractor. This is consistent with independent spatial and object-based inhibitory mechanisms. Therefore, we suggest that distractor inhibition is maintained in cortical visual areas with allocentric maps which then feeds into oculomotor areas for saccade planning.

Macrophages protect against sensory axon degeneration in diabetic neuropathy
Diabetic peripheral neuropathy (DPN) is the most common peripheral nervous system complication of diabetes, causing sensory loss and debilitating neuropathic pain. Although the onset and progression of DPN have been linked with dyslipidemia and hyperglycemia, the contribution of inflammation in the pathogenesis of DPN has not been investigated. Here, we use a High Fat High Fructose Diet (HFHFD) to model DPN and the diabetic metabolic syndrome in mice. Diabetic mice develop persistent heat hypoalgesia after three months, but a reduction in epidermal skin innervation only manifests at 6 months. Using single-cell sequencing, we find that CCR2+ macrophages infiltrate the sciatic nerves of diabetic mice well before axonal degeneration is observed. We show that these infiltrating macrophages share gene expression similarities with nerve crush-induced macrophages and express neurodegeneration-associated microglia marker genes although there is no axon loss or demyelination yet. Inhibiting this macrophage recruitment in diabetic mice by genetically or pharmacologically blocking CCR2 signaling results in a more severe heat hypoalgesia and accelerated skin denervation. These findings identify a novel neuroprotective recruitment of macrophages into peripheral nerves of diabetic mice that delays the onset of terminal axonal degeneration, thereby reducing sensory loss. Potentiating and sustaining this early neuroprotective immune response in patients represents, therefore, a potential means to reduce or prevent DPN.

Urolithin A improves Alzheimers disease cognition and restores mitophagy and lysosomal functions
BackgroundCompromised autophagy, including impaired mitophagy and lysosomal function, is thought to play a pivotal role in Alzheimers disease (AD). Urolithin A (UA) is a gut microbial metabolite of ellagic acid that stimulates mitophagy. The effects of early and/or long-term treatment, as well as more detailed mechanisms of action, are not known.

MethodsWe addressed these questions in three mouse models of AD, and behavioral, electrophysiological and biochemistry assays were performed.

ResultsLong-term UA treatment significantly improved learning, memory and olfactory function in different AD transgenic mice. UA also reduced A{beta} and Tau pathologies, and improved long-term potentiation. We found that UA activated autophagy/mitophagy via increasing lysosomal functions. At the cellular level, UA improved lysosomal function and normalized lysosomal cathepsins, especially targeting cathepsin Z, to restore lysosomal function in AD, indicating the important role of cathepsins in UA-induced therapeutic effects of AD.

ConclusionsCollectively, our study highlights the importance of lysosomal dysfunction in AD etiology, and points to the high translational potential of UA.

Arc mediates intercellular synaptic plasticity via IRSp53-dependent extracellular vesicle biogenesis.
Current models of learning and memory have focused on cell-autonomous regulation of synaptic strength; however, intercellular signaling between cells in the brain is critical for normal cognition. The immediate early gene Arc is a repurposed retrotransposon critical for long-term forms of synaptic plasticity and memory. Arc protein forms virus-like capsids released in extracellular vesicles (EVs) that signal cell-to-cell. Here, we find that long-term potentiation (LTP) stimuli induce the biogenesis of Arc EVs by recruiting the I-BAR protein IRSp53 to dendrites, which facilitates Arc capsid assembly and release. Arc EVs transfer Arc protein and mRNA to neighboring neurons, where translation of transferred Arc mRNA induces a loss of surface AMPA-type glutamate receptors. These results show that Arc EVs mediate non-cell autonomous long-term depression (LTD), revealing an intercellular form of synaptic plasticity that may be critical for memory consolidation.

Cortical multi-area model with joint excitatory-inhibitory clusters accounts for spiking statistics, inter-area propagation, and variability dynamics
The primate brain uses billions of interacting neurons to produce macroscopic dynamics and behavior, but current methods only allow neuroscientists to investigate a subset of the neural activity. Computational modeling offers an alternative testbed for scientific hypotheses, by allowing full control of the system. Here, we test the hypothesis that local cortical circuits are organized into joint clusters of excitatory and inhibitory neurons by investigating the influence of this organizational principle on cortical resting-state spiking activity, inter-area propagation, and variability dynamics. The model represents all vision-related areas in one hemisphere of the macaque cortex with biologically realistic neuron densities and connectivities, expanding on a previous unclustered model of this system. Each area is represented by a square millimeter microcircuit including the full density of neurons and synapses, avoiding downscaling artifacts and testing cortical dynamics at the natural scale. We find that joint excitatory-inhibitory clustering normalizes spiking activity statistics in terms of firing rate distributions and inter-spike interval variability. A comparison with data from cortical areas V1, V4, FEF, 7a, and DP shows that the clustering enables the resting-state activity of especially higher cortical areas to be better captured. In addition, we find that the clustering supports signal propagation across all areas in both feedforward and feedback directions with reasonable latencies. Finally, we also show that localized stimulation of the clustered model quenches the variability of neural activity, in agreement with experimental observations. We conclude that joint clustering of excitatory and inhibitory neurons is a likely organizational principle of local cortical circuits, supporting resting-state spiking activity statistics, inter-area propagation, and variability dynamics.

LSD Modulates Proteins Involved in Cell Proteostasis, Energy Metabolism and Neuroplasticity in Human Brain Organoids
The effects of psychedelics encompass modulation of subjective experience, neuronal plasticity, brain activity and connectivity, constituting a complex phenomenon. Underlying these effects, molecular changes at the protein level are expected. Proteomic analysis of human brain cells can elicit a comprehensive view of proteins and biological processes regulated within the central nervous system. To explore the molecular pathways influenced by lysergic acid diethylamide (LSD), we utilized mass spectrometry-based proteomics on human brain organoids. This approach allowed for an in-depth analysis of the proteomic alterations induced by LSD, providing insights into its effects at the molecular level within a brain-like environment. Alterations in proteostasis and energy metabolism, which are required for neural plasticity, were observed. Alongside, we identified changes in protein synthesis, folding, autophagy, and proteasomal degradation, as well as in glycolysis, oxidative phosphorylation, cytoskeleton regulation, and neurotransmitter release, providing a comprehensive view of the regulation of cellular process by LSD exposure. Furthermore, the ability of LSD to induce plasticity in human brain cells was corroborated through complementary in vitro experiments focusing on neurite outgrowth. This study sheds light on the specific proteins that LSD influences, thereby enhancing neurite extension and plasticity.

Metabolic resistance of Abeta3pE-42, epitope of the anti-Alzheimer therapeutic antibody, donanemab.
Amyloid beta peptide (Abeta) starting with pyroglutamate (pE) at position 3 and ending at position 42 (Abeta3pE-42) is a dominant species that accumulates in Alzheimer's disease (AD) brain. Consistently, a therapeutic antibody raised against this species, donanemab, has succeeded in recent clinical trials. While the primary Abeta species produced physiologically is Abeta1-40/42, an explanation for how and why this physiological Abeta is converted to the pathological form has remained elusive. The conversion of Abeta1-42 to Abeta3pE-42 is likely to take place after deposition of Abeta1-42 given that Abeta3pE-42 plaques arise significantly later than Abeta1-42 deposition in the brains of single App knock-in and APP-transgenic mice. Here, we present experimental evidence that accounts for the aging-associated Abeta3pE-42 deposition. Abeta3pE-42 is metabolically more stable than other AbetaX-42 species. Consistently, newly generated knock-in mice, AppNL-(deltaDA)-F and AppNL-(deltaDA)-Q-F, showed no detectable Abeta pathology even after aging. In addition, a deficiency of NEP facilitated Abeta3pE-42 deposition. Abeta3pE-42 is thus likely to be a probabilistic by-product of Abeta1-42 metabolism that selectively accumulates over a long-time range of brain aging.

Transcriptome-based screening in TARDBP/TDP-43 knock-in motor neurons identifies the NEDD8-activating enzyme inhibitor MLN4924
A growing body of knowledge implicates perturbed RNA homeostasis in amyotrophic lateral sclerosis (ALS), a neurodegenerative disease that currently has no cure and few available treatments. Dysregulation of the multifunctional RNA-binding protein TDP-43 is increasingly regarded as a convergent feature of this disease, evidenced at the neuropathological level by the detection of TDP-43 pathology in most patient tissues, and at the genetic level by the identification of disease-associated mutations in its coding gene TARDBP. To characterize the transcriptional landscape induced by TARDBP mutations, we performed whole-transcriptome profiling of motor neurons differentiated from two knock-in iPSC lines expressing the ALS-linked TDP-43 variants p.A382T or p.G348C. Our results show that the TARDBP mutations significantly altered the expression profiles of mRNAs and microRNAs of the 14q32 cluster in MNs. Using mutation-induced gene signatures and the Connectivity Map database, we identified compounds predicted to restore gene expression toward wild-type levels. Among top-scoring compounds selected for further investigation, the NEDD8-activating enzyme inhibitor MLN4924 effectively improved cell viability and neuronal activity, highlighting a possible role for protein post-translational modification via NEDDylation in the pathobiology of TDP-43 in ALS.

A deep-learning strategy to identify cell types across species from high-density extracellular recordings
High-density probes allow electrophysiological recordings from many neurons simultaneously across entire brain circuits but fail to determine each recorded neuron's cell type. Here, we develop a strategy to identify cell types from extracellular recordings in awake animals, opening avenues to unveil the computational roles of neurons with distinct functional, molecular, and anatomical properties. We combine optogenetic activation and pharmacology using the cerebellum as a testbed to generate a curated ground-truth library of electrophysiological properties for Purkinje cells, molecular layer interneurons, Golgi cells, and mossy fibers. We train a semi-supervised deep-learning classifier that predicts cell types with greater than 95% accuracy based on waveform, discharge statistics, and layer of the recorded neuron. The classifier's predictions agree with expert classification on recordings using different probes, in different laboratories, from functionally distinct cerebellar regions, and across animal species. Our approach provides a general blueprint for cell-type identification from extracellular recordings across the brain.

Widespread latent hyperactivity of nociceptors outlasts enhanced avoidance behavior following incision injury
Nociceptors with somata in dorsal root ganglia (DRGs) exhibit an unusual readiness to switch from an electrically silent state to a hyperactive state of tonic, nonaccommodating, low-frequency, irregular discharge of action potentials (APs). Ongoing activity (OA) during this state is present in vivo in rats months after spinal cord injury (SCI), and has been causally linked to SCI pain. OA induced by various neuropathic conditions in rats, mice, and humans is retained in nociceptor somata after dissociation and culturing, providing a powerful tool for investigating its mechanisms and functions. An important question is whether similar nociceptor OA is induced by painful conditions other than neuropathy. The present study shows that probable nociceptors dissociated from DRGs of rats subjected to postsurgical pain (induced by plantar incision) exhibit OA. The OA was most apparent when the soma was artificially depolarized to a level within the normal range of membrane potentials where large, transient depolarizing spontaneous fluctuations (DSFs) can approach AP threshold. This latent hyperactivity persisted for at least 3 weeks, whereas behavioral indicators of affective pain (hindpaw guarding and increased avoidance of a noxious substrate in an operant conflict test) persisted for 1 week or less. An unexpected discovery was latent OA in neurons from thoracic DRGs that innervate dermatomes distant from the injured tissue. The most consistent electrophysiological alteration associated with OA was enhancement of DSFs. Potential in vivo functions of widespread, low-frequency nociceptor OA consistent with these and other findings are to amplify hyperalgesic priming and to drive anxiety-related hypervigilance.

Identification and characterization of a potentially novel dorsal cutaneous muscle in rodents
In the course of performing a detailed dissection of adult rat to map the cutaneous nerves of cervical, thoracic, and lumbar levels a small and unexpected structure was isolated. It appeared to be a cutaneous striated muscle and was observed in both male and female rats and in mice but absent from cats and humans. With the skin reflected laterally from midline, the muscle lies closely apposed to the lateral border of the Thoracic Trapezius (Spinotrapezius) muscle and is easily missed in standard gross dissections. Focussed prosections were performed to identify the origin, insertion, and course of gross innervation. Identification of each of these elements showed them to be distinct from the nearby Trapezius and Cutaneous Trunci (Cutaneous Maximus in mouse) muscles. The striated muscle nature of the structure was validated with whole-mount microscopy. Consulting a range of published rodent anatomical atlases and gross anatomical experts revealed no prior descriptions. This preliminary report is an opportunity for the anatomical and research communities to provide input to either confirm the novelty of this muscle or refer to prior published descriptions in rodents or other species while the muscle, its innervation, and function are further characterized. Presuming this muscle is indeed novel, the name 'Cutaneous scapularis muscle' is proposed in accord with general principles of the anatomical field.

Charting the Spatial Transcriptome of the Human Cerebral Cortex at Single-Cell Resolution
In our pursuit of creating a comprehensive human cortical atlas to understand human intelligence, we examined the single-nuclei transcriptomes of 307,738 cells alongside spatial transcriptomics data from 46,948 VISIUM spots and 1,355,582 Stereo cells. Atlases reveal distinct expression patterns and spatial arrangements of cortical neural cell types. Glutamatergic neurons exhibit precise laminar patterns, often mirroring expression patterns in adjacent cortical regions. Overlaying our atlas with functional networks delineated substantial correlations between neural cell types and cortical region function. Notably, regions involved in processing sensory information (pain) display a pronounced accumulation of extratelencephalic neurons. Additionally, our atlas enabled precise localization of the thicker layer 4 of the visual cortex and an in-depth study of the stabilized subplate structure, known as layer 6b, revealed specific marker genes and cellular compositions. Collectively, our research sheds light on the cellular foundations of the intricate and intelligent regions within the human cortex.

Auditory stimuli extend the temporal window of visual integration by modulating alpha-band oscillations
In the multisensory environment, the interactions between inputs from different sensory modalities are not fully understood. Here, we conducted an electroencephalography (EEG) experiment to investigate how auditory stimuli shape the temporal window of visual integration in human subjects. Participants were presented with two consecutive visual flashes, either accompanied by an auditory beep or without, and were asked to report their perception of one or two flashes. Behaviorally, we found that the introduction of auditory input induced a longer temporal window for integration. Alpha frequency analysis further revealed that the presence of auditory stimuli led to poststimulus alpha frequency degradation, positively correlating with the prolonged temporal window, supporting the idea that alpha oscillations represent the temporal window of visual integration. Further exploration of prestimulus alpha oscillations revealed that auditory stimuli diminished the predictive role of prestimulus alpha frequency while enhancing the predictive role of prestimulus alpha phase in determining perceptual outcomes. To unveil the underlying mechanism, we developed a computational model based on the phase-resetting hypothesis and the perceptual cycle theory, successfully replicating key behavioral and neural findings. Together, our results suggest that concurrent auditory input extends the temporal window of visual integration by resetting the phase of alpha oscillations in the visual cortex, leading to alpha frequency degradation.

Incorporation of a cost of deliberation time in perceptual decision making
Many decisions benefit from the accumulation of evidence obtained sequentially over time. In such circumstances, the decision maker must balance speed against accuracy, and the nature of this tradeoff mediates competing desiderata and costs, especially those associated with the passage of time. A neural mechanism to achieve this balance is to accumulate evidence in suitable units and to terminate the deliberation when enough evidence has accrued. To accommodate time costs, it has been hypothesized that the criterion to terminate a decision may become lax as a function of time. Here we tested this hypothesis by manipulating the cost of time in a perceptual choice-reaction time task. Participants discriminated the direction of motion in a dynamic random-dot display, which varied in difficulty across trials. After each trial, they received feedback in the form of points based on whether they made a correct or erroneous choice. They were instructed to maximize their points per unit of time. Unbeknownst to the participants, halfway through the experiment, we increased the time pressure by canceling a small fraction of trials if they had not made a decision by a provisional deadline. Although the manipulation canceled less than 5% of trials, it induced the participants to make faster decisions while lowering their decision accuracy. The pattern of choices and reaction times were explained by bounded drift-diffusion. In all phases of the experiment, stopping bounds were found to decline as a function of time, consistent with the optimal solution, and this decline was exaggerated in response to the time-cost manipulation.

Recording gamma-secretase activity in living mouse brains
{gamma}-Secretase plays a pivotal role in the central nervous system. Our recent development of genetically encoded Forster resonance energy transfer (FRET)-based biosensors has enabled the spatiotemporal recording of gamma-secretase activity on a cell-by-cell basis in live neurons in culture. Nevertheless, how {gamma}-secretase activity is regulated in vivo remains unclear. Here we employ the near-infrared (NIR) C99 720-670 biosensor and NIR confocal microscopy to quantitatively record gamma-secretase activity in individual neurons in living mouse brains. Intriguingly, we uncovered that gamma-secretase activity may influence the activity of gamma-secretase in neighboring neurons, suggesting a potential "cell non-autonomous" regulation of gamma-secretase in mouse brains. Given that gamma-secretase plays critical roles in important biological events and various diseases, our new assay in vivo would become a new platform that enables dissecting the essential roles of gamma-secretase in normal health and diseases.

Functional magnetic resonance imaging of the lumbosacral cord during a lower extremity motor task
Blood-oxygen-level dependent (BOLD) functional magnetic resonance imaging (fMRI) can be used to map neuronal function in the cervical cord, yet conclusive evidence supporting its applicability in the lumbosacral cord is still lacking. This study aimed to (i) demonstrate the feasibility of BOLD fMRI in mapping neuronal activation in the lumbosacral cord during a unilateral lower extremity motor task and (ii) investigate the impact of echo time (TE) on the BOLD effect size. Twelve healthy volunteers underwent BOLD fMRI using four reduced-field-of-view single-shot gradient-echo echo planar imaging sequences, all with the same geometry but different TE values ranging from 20 to 42 ms. Each sequence was employed to acquire a single 6-minute rest run and two 10-minute task runs, which included alternating 15-second blocks of rest and unilateral ankle dorsi- and plantar flexion. We detected lateralized task-related neuronal activation at neurological levels S4 to L1, centered at the ipsilateral (right) ventral spinal cord but also extending into the ipsilateral dorsal spinal cord. This pattern of activation is consistent with our current understanding of spinal cord organization, wherein lower motor neurons are located in the ventral gray matter horn, while sensory neurons of the proprioceptive pathway, activated during the movement, are located in the dorsal horns. At the subject level, BOLD activation showed considerable variability but was lateralized in all participants. The highest BOLD effect size within the ipsilateral ventral spinal cord was observed at TE=42 ms. Sequences with a shorter TE (20 and 28 ms) also detected activation in the medioventral part of the spinal cord, likely representing a large vein effect. In summary, our results demonstrate the feasibility of detecting neuronal activation in the lumbosacral cord induced by voluntary lower limb movements. BOLD fMRI in the lumbosacral cord has significant implications for assessing motor function and its alterations in disease or after spinal cord injury.