bioRxiv Subject Collection: Neuroscience's Journal

Connectivity in the human and the monkey brain probes causal involvement of the fornix in Mild Cognitive Impairment and Alzheimer's Disease
Alzheimer's disease (AD) is characterised by memory loss and severe deficits in cognitive function associated with neural degeneration in a network of brain regions. However, little is known about those regions' connectivity patterns and how that differs from mild cognitive impairment (MCI) or healthy aging. To address that, we used diffusion-weighted MRI to determine connectivity across 11 key memory-related regions and their unique set of connections (connectivity fingerprints) to 14 white matter (WM) tracts. One WM tract particularly important for memory, and attractive target for therapeutic interventions in AD, is the fornix. However, determining fornix-specific contributions to memory deficits or therapeutic benefits is difficult, partly because the fornix carries numerous subcortical and cortical projections. To explore that, we additionally examined MRI-derived connectivity across homologous structures in non-human primates before and after fornix transections. We report several important findings. First, that connectivity between the hippocampus and the anterior thalamus (ATh) is strongly compromised in cognitive decline, as is fornix integrity. We also found strong reductions in the hippocampus-fornix and ATh-fornix connectivity in AD, demonstrating that fingerprint divergence across groups in hippocampal CA1 and ATh can identify differences between people with AD and MCI. In AD, we observed also elevated connectivity between WM tracts and the hippocampus or the ATh, suggesting a compensatory mechanism, which, importantly, depends on a viable fornix. We finally demonstrate that certain thalamic nuclei and hippocampal subfields link through the retrosplenial cortex in both species, highlighting its potential role as an alternative target for interventions in memory disorders.

Characterizing vascular function in mouse models of Alzheimer's disease, atherosclerosis, and mixed Alzheimer's and atherosclerosis
SignificanceAlzheimers disease does not occur in isolation and there are many comorbidities associated with the disease - especially diseases of the vasculature. Atherosclerosis is a known risk factor for the subsequent development of Alzheimers disease, therefore understanding how both diseases interact will provide a greater understanding of co-morbid disease progression and aid the development of potential new treatments.

AimThe current study characterizes hemodynamic responses and cognitive performance in APP/PS1 Alzheimers mice, atherosclerosis mice, and a mixed disease group (APP/PS1 & atherosclerosis) between the ages of 9 and 12 months.

ApproachWhisker-evoked hemodynamic responses and recognition memory were assessed in awake mice, immunohistochemistry to assess amyloid pathology, and histology to characterize atherosclerotic plaque load.

ResultsWe observed hemodynamic deficits in atherosclerosis mice (vs Alzheimers, mixed disease or wild-type mice), with reduced short-duration stimulus-evoked hemodynamic responses occurring when there was no concurrent locomotion during the stimulation period. Mixed Alzheimers and atherosclerosis models did not show differences in amyloid beta coverage in the cortex or hippocampus or atherosclerotic plaque burden in the aortic arch vs relevant Alzheimers or atherosclerosis controls. Consistent with the subtle vascular deficits and no pathology differences, we also observed no difference in performance on the novel object recognition task across groups.

ConclusionsThese results emphasize the importance of experimental design for characterizing vascular function across disease groups, as locomotion and stimulus duration impacted the ability to detect differences between groups. Whilst atherosclerosis did reduce hemodynamic responses, these were recovered in the presence of co-occurring Alzheimers disease which may provide targets for future studies to explore the potentially contrasting vasodilatory mechanisms these diseases impact.

Microglial engulfing of glutamatergic inputs and diminished excitability of D1 medium spiny neurons of the nucleus accumbens by peripheral inflammatory insult
Neuroimmune responses to systemic inflammation can generate anxiodepressive behaviors and psychomotor slowing. The nucleus accumbens (NAc) is a neural hub encoding mood and motivation that contributes to the locomotor and mood dampening effects of neuroinflammation. Dopamine receptor 1 mediums spiny neurons (D1-MSNs) of the NAc regulate locomotor activity, motivated behavior and emotional states and are modulated by microglial reactivity. Here, we evaluated sickness- and anxiety-like behaviors along with D1-MSN activity and microglial responses in the NAc to systemic lipopolysaccharide (LPS) administration. LPS stimulated anxiety-like behavior, blunted locomotion and reduced cFos expression in D1-MSNs of the NAc core and shell of male mice. These effects associated with reduced excitatory inputs (EPSCs) onto D1-MSNs as measured by whole cell patch-clamp. To determine if microglia contribute to changes in MSN activity, Ca2+ imaging of primary cultures containing NAc neurons with or without primary NAc microglia was performed. The presence of microglia decreased the activity of LPS-treated MSNs in response to dopamine and glutamate application and LPS stimulated microglial phagocytosis of MSN processes in co-cultures. Immunohistochemical analyses revealed that in vivo LPS treatment enhanced morphological indices of microglia reactivity and engulfment of vesicular glutamate transporter 1 (VGLUT1) inputs in the NAc. Our results suggest that LPS reduces locomotion and stimulates anxiety via increasing microglia engulfment of excitatory inputs onto D1-MSNs, and highlight changes in NAc microglia phagocytic activity in the behavioral consequences of neuroinflammation.

Synaptic acetylcholine induces sharp wave ripples in the basolateral amygdala through nicotinic receptors
While the basolateral amygdala (BLA) is critical in the consolidation of emotional memories, mechanisms underlying memory consolidation in this region are not well understood. In the hippocampus, memory consolidation depends upon network signatures termed sharp wave ripples (SWR). These SWRs largely occur during states of awake rest or slow wave sleep and are inversely correlated with cholinergic tone. While high frequency cholinergic stimulation can inhibit SWRs through muscarinic acetylcholine receptors, it is unclear how nicotinic acetylcholine receptors or different cholinergic firing patterns may influence SWR generation. SWRs are also present in BLA in vivo. Interestingly, the BLA receives extremely dense cholinergic inputs, yet the relationship between acetylcholine (ACh) and BLA SWRs is unexplored. Here, using brain slice electrophysiology in male and female mice, we show that brief stimulation of ACh inputs to BLA reliably induces SWRs that resemble those that occur in the BLA in vivo. Repeated ACh-SWRs are induced with single pulse stimulation at low, but not higher frequencies. ACh-SWRs are driven by nicotinic receptors which recruit different classes of local interneurons and trigger glutamate release from external inputs. In total, our findings establish a previously undefined mechanism for SWR induction in the brain. They also challenge the previous notion of neuromodulators as purely modulatory agents gating these events but instead reveal these systems can directly instruct SWR induction with temporal precision. Further, these results intriguingly suggest a new role for the nicotinic system in emotional memory consolidation.

Significance StatementSharp wave ripples represent a key network signature believed to be important in memory consolidation. These network events have been largely studied in the hippocampus and are suppressed by the basal forebrain cholinergic system. Sharp wave ripples also occur in the basolateral amygdala, a region critically involved in emotional memory consolidation. Here, we show a novel mechanism by which low frequency stimulation of synaptic acetylcholine in basolateral amygdala brain slices can reliably induce sharp wave ripples through a nicotinic receptor-mediated mechanism. These findings update the view of neuromodulatory systems in sharp wave ripple induction, moving past a purely modulatory role for these systems and instead establish a role where modulators, like acetylcholine, can directly drive SWRs with temporal precision.

Asynchronous subunit transitions precede acetylcholine receptor activation
Rapid communication at synapses is facilitated by postsynaptic receptors, which convert a chemical signal into an electrical response. In the case of ligand-gated ion channels, agonist binding triggers rapid transition through a series of intermediate states leading to a transient open-pore conformation. These transitions are usually framed in terms of a mechanism where agonist binding and channel activation are separate events. Here, we collect cryo-EM images over a range of agonist concentrations to define structures of the muscle-type nicotinic acetylcholine receptor in unliganded, mono-liganded, and di-liganded states. We show that agonist binding to a single agonist site stabilizes an intermediate state where an entire principal agonist-binding subunit has transitioned to an active-like conformation, while the other unoccupied principal subunit remains inactive, albeit poised for activation. Binding of agonist to the second agonist site fully activates the remaining subunits leading to hydration of the ion pore. Uniting this cryo-EM derived intermediate structure with single-channel recordings leads to a model where individual acetylcholine receptor subunits asynchronously undergo conformational transitions, and thus a sequential activation mechanism that has implications for the entire superfamily of pentameric ligand-gated ion channels.

MEG signals reveal arm posture coding and intrinsic movement plans in parietofrontal cortex
Movement planning processes must account for body posture to accurately convert sensory signals into movement plans. While movement plans can be computed relative to the world (extrinsic), intrinsic muscle commands tuned for current limb posture are ultimately needed to execute spatially accurate movements. The whole-brain topology and dynamics of this process are largely unknown. Here, we use high spatiotemporal resolution magnetoencephalography (MEG) in humans combined with a Pro-/Anti-wrist pointing task with 2 opposing forearm postures to investigate this question. First, we computed cortical source activity in 16 previously identified bilateral cortical areas (Alikhanian, et al., Frontiers in Neuroscience 2013). We then contrasted oscillatory activity related to opposing wrist postures to find posture coding and test when and where extrinsic and intrinsic motor codes occurred. We found a distinct pair of overlapping networks coding for posture (predominantly in {gamma} band) vs. posture-specific movement plans ( and {beta}). Some areas (e.g., pIPS) only showed extrinsic motor coding, and others (e.g., AG) only showed intrinsic coding, but the majority showed both types of codes. In the latter case, intrinsic codes appeared slightly before extrinsic codes and persisted in parallel across different cortical areas. These findings are consistent with two cortical networks for 1) direct feed-forward sensorimotor transformations to intrinsic muscle coordinates (for rapid control) and 2) computations of extrinsic spatial coordinates, possibly for use in higher-level aspects of visually-guided action, such as spatial updating and internal performance monitoring.

Significance statement / author summaryIt is thought that the brain incorporates posture into extrinsic spatial codes to compute intrinsic (muscle-centered) motor commands, but the whole-brain temporal dynamics of this process is unknown. Here we employed human magneto-encephalography (MEG) to track this process across 16 bilateral cortical sites. We identified two, largely overlapping subnetworks for posture-dependent intrinsic codes, and extrinsic spatial coding. Surprisingly, the direct transformation from sensorimotor coordinates to intrinsic commands preceded the appearance of extrinsic codes, suggesting that extrinsic motor codes are derived from intrinsic codes for higher-level cognitive purposes.

Hydrogel encapsulation of a designed fluorescent protein biosensor for continuous measurements of sub-100 nanomolar nicotine
The reinforcing and addictive properties of nicotine result from concentration- and time-dependent activation, desensitization, and upregulation of nicotinic acetylcholine receptors. However, time-resolved [nicotine] measurement in people who consume nicotine is challenging, as current approaches are expensive, invasive, tedious, and discontinuous. To address the challenge of continuous nicotine monitoring in human biofluids, we report the encapsulation of a purified, previously developed fluorescent biosensor protein, iNicSnFR12, into acrylamide hydrogels and polyethylene glycol diacrylate (PEGDA) hydrogels. We optimized the hydrogels for optical clarity and straightforward slicing. With fluorescence photometry of the hydrogels in a microscope and an integrated miniscope, [nicotine] is detected within a few min at the smoking- and vaping-relevant level of 10 - 100 nM (1.62 - 16.2 ng/ml), even in a 250 {micro}m thick hydrogel at the end of 400 {micro}m dia multimode fiber optic. Concentration-response relations are consistent with previous measurements on isolated iNicSnFR12. Leaching of iN-icSnFR12 from the hydrogel and inactivation of iNicSnFR12 are minimal for several days, and nicotine can be detected for at least 10 months after casting. This work provides the molecular, photophysical, and mechanical bases for personal, wearable continuous [nicotine] monitoring, with straightforward extensions to existing, homologous "iDrugSnFR" proteins for other abused and prescribed drugs.

Integrated phenomenology and brain connectivity demonstrate changes in nonlinear processing in jhana advanced meditation
We present a neurophenomenological case study investigating distinct neural connectivity regimes during an advanced concentrative absorption meditation called jhana (ACAM-J),characterized by highly-stable attention and mental absorption. Using EEG recordings and phenomenological ratings (29 sessions) from a meditator with +20,000 hours of practice, we evaluated connectivity metrics tracking distinct large-scale neural interactions: nonlinear (WSMI and Directed Information), capturing non-oscillatory dynamics; and linear (WPLI) connectivity metrics, capturing oscillatory synchrony. Results demonstrate ACAM-J are better distinguished by non-oscillatory compared to oscillatory dynamics across multiple frequency ranges. Furthermore, combining attention-related phenomenological ratings with WSMI improves Bayesian decoding of ACAM-J compared to neural metrics alone. Crucially, deeper ACAM-J indicate an equalization of feedback and feedforward processes, suggesting a balance of internallyand externally-driven information processing. Our results reveal distinct neural dynamics during ACAM-J, offering insights into refined conscious states and highlighting the value of nonlinear neurophenomenological approaches to studying attentional states.

Hyperactive neuronal networks facilitate tau spread in an Alzheimer's disease mouse model
Pathological tau spreads throughout the brain along neuronal connections in Alzheimers disease (AD), but the mechanisms that underlie this process are poorly understood. Given the high incidence and deleterious consequences of epileptiform activity in AD, we hypothesized neuronal hyperactivity and seizures are key factors in tau spread. To examine these interactions, we created a novel mouse model involving the cross of targeted recombination in active populations (TRAP) mice and the 5 times familial AD (5XFAD; 5X-TRAP) model allowing for the permanent fluorescent labelling of neuronal activity. To establish a causal role of seizures in tau spread, we seeded mice with human AD brain-derived tau lysate and induced seizures with pentylenetetrazol (PTZ) kindling. Comprehensive brain mapping of tau pathology and neuronal activity revealed that basal hyperactivity in 5X-TRAP mice was associated with increased tau spread, which was exacerbated by seizure induction through activated networks and correlated with memory deficits. Computational modeling revealed that anterograde tau spread was elevated in 5X-TRAP mice and that regional neuronal activity was predictive of tau spread to that brain region. On a cellular level, we found that in both saline and PTZ-treated 5X-TRAP mice, hyperactive neurons disproportionately contributed to the spread of tau. Further, we found that Synaptogyrin-3, a synaptic vesicle protein that interacts with tau, was increased following PTZ kindling in 5X-TRAP mice, possibly indicative of a synaptic mechanism underlying seizure-exacerbated tau spread. Importantly, postmortem AD brain tissue from patients with a history of seizures showed increased tau pathology in patterns indicative of increased spread and increased Synaptogyrin-3 levels compared to those without seizures. Overall, our study identifies neuronal hyperactivity and seizures as key factors underlying the pathobiological and cognitive progression of AD. Therapies targeting these factors should be tested clinically to slow tau spread and AD progression.

Dynamic Regulation Of The Chromatin Environment By ASH1L Modulates Human Neuronal Structure And Function
Precise regulation of the chromatin environment through post-translational histone modification modulates transcription and controls brain development. Not surprisingly, mutations in a large number of histone-modifying enzymes underlie complex brain disorders. In particular, the histone methyltransferase ASH1L modifies histone marks linked to transcriptional activation and has been implicated in multiple neuropsychiatric disorders. However, the mechanisms underlying the pathobiology of ASH1L-asociated disease remain underexplored. We generated human isogenic stem cells with a mutation in ASH1Ls catalytic domain. We find that ASH1L dysfunction results in reduced neurite outgrowth, which correlates with alterations in the chromatin profile of activating and repressive histone marks, as well as the dysregulation of gene programs important for neuronal structure and function implicated in neuropsychiatric disease. We also identified a novel regulatory node implicating both the SP and Kruppel-like families of transcription factors and ASH1L relevant to human neuronal development. Finally, we rescue cellular defects linked to ASH1L dysfunction by leveraging two independent epigenetic mechanisms that promote transcriptional activation. In summary, we identified an ASH1L-driven epigenetic and transcriptional axis essential for human brain development and complex brain disorders that provide insights into future therapeutic strategies for ASH1L-related disorders.

Overactivation of prefrontal astrocytes impairs cognition through the metabolic pathway of central kynurenines
Astrocyte dysfunctions have long been implicated in psychiatric and cognitive disorders, yet the precise mechanisms underlying this association remain elusive. Here, we show that chemogenetic activation of prefrontal astrocytes in mice impairs short-term memory and sensorimotor gating and attenuates the activation of parvalbumin (PV) interneurons in the prefrontal cortex. These alterations are accompanied by increases in prefrontal levels of kynurenic acid (KYNA), a key metabolite of the kynurenine (KYN) pathway, known to be produced by astrocytes, which serves as an endogenous antagonist of NMDA receptors. Pharmacological inhibition of kynurenine aminotransferase II, the key enzyme mediating the transamination of KYN to KYNA, reinstates the astrocyte-mediated impairments in short-term memory and sensorimotor gating, and normalizes the deficits in prefrontal PV interneuron activation. Our study identifies a mechanistic link between overactivation of prefrontal astrocytes, increased production of KYNA, and cognitive as well as cellular dysfunctions involved in major psychiatric disorders and beyond.

The efficacy of resting-state fMRI denoising pipelines for motion correction and behavioural prediction.
Resting-state functional magnetic resonance imaging (rs-fMRI) is a pivotal tool for mapping the functional organization of the brain and its relation to individual differences in behaviour. One challenge for the field is that rs-fMRI signals are contaminated by multiple sources of noise that can contaminate these rs-fMRI signals, affecting the reliability and validity of any derivative phenotypes and attenuating their correlations with behaviour. Here, we investigate the efficacy of different noise mitigation pipelines, including white-matter and cerebrospinal fluid regression, independent component analysis (ICA) - based artefact removal, volume censoring, global signal regression (GSR), and diffuse cluster estimation and regression (DiCER), in simultaneously achieving two objectives: mitigating motion-related artifacts and augmenting brain-behaviour associations. Our analysis, which employed three distinct quality control metrics to evaluate motion influence and a kernel ridge regression for behavioural predictions of 81 different behavioural variables across two independent datasets, revealed that no single pipeline universally excels at achieving both objectives consistently across different cohorts. Pipelines combining ICA-FIX and GSR demonstrate a reasonable trade-off between motion reduction and behavioural prediction performance, but inter-pipeline variations in predictive performance are modest.

The effects of varying intensities of unilateral handgrip fatigue on bilateral movement
The human ability to maintain adequate movement quality despite muscle fatigue is of critical importance to master physically demanding activities of daily life and for retaining independence following motor impairments. Many real-life situations call for asymmetrical activation of extremity muscles leading to unilateral manifestations of muscle fatigue. Repeated unilateral handgrip contractions at submaximal force have been shown to be associated with neural dynamics in both contralateral and ipsilateral cortical motor areas and improved response times of the contralateral, unfatigued homologue in a button-press task. However, it remains unclear whether the observed improvement in contralateral response latency translates into higher-level benefits in movement quality.

To investigate this, 30 healthy participants underwent unilateral handgrip fatiguing tasks at 5%, 50%, and 75% of maximum voluntary contraction (MVC) force. Subsequently, bimanual movement quality was assessed in an object-hit task using a Kinarm robot.

The protocol at 50% and 75% of MVC elicited clear signs of muscle fatigue compared to the control condition (5%) measured by a decline in force, post-exercise deterioration in MVC, characteristic changes in surface electromyography magnitudes, and increases in ratings of perceived exertion. No change was observed on kinematic measures in the object-hit task for both arms indicating that unilateral handgrip fatigue did not elicit measurable effects on higher-level movement quality on the ipsilateral or contralateral homologue. Previously reported improvements on contralateral response latency were not found to translate into advanced movement quality benefits.

Decoding task representations that support generalization in hierarchical task
Task knowledge is encoded hierarchically such that complex tasks are composed of simpler tasks. This compositional organization also supports generalization to facilitate learning of related but novel complex tasks. To study how the brain implements composition and generalization in hierarchical task learning, we trained human participants on two complex tasks that shared a simple task and tested them on a novel complex task whose composition could be inferred via the shared simple task. Behaviorally, we observed faster learning of the novel complex task than control tasks (i.e., behavioral generalization effect). Using electroencephalogram (EEG) data, we could decode the constituent simple tasks when a complex task was performed (i.e., EEG composition effect). Crucially, the shared simple task, although not part of the novel complex task, could be reliably decoded from the novel complex task. The decoding strength was also correlated with EEG composition effect and behavioral generalization effect. The findings demonstrate how generalization in task learning is implemented via task reinstatement.

Significance StatementHumans can generalize knowledge of existing tasks to accelerate the learning of new tasks. We hypothesize that generalization is achieved by decomposing a complex task into simple (sub)tasks and reusing the simple tasks to infer the structure of a new complex task and build it. Using electroencephalogram data, we showed that constituent simple tasks can be decoded from of humans learning new complex tasks. Crucially, when the structure of a new complex task can be inferred from simple tasks, the simple tasks can be decoded from the new complex task, even when they are not part of the new complex task. These findings demonstrate the importance of the reinstatement of simple tasks in task learning through generalization.

Similarity in Early Life Stress Exposure is Associated with Similarity in Neural Representations in Early Adulthood
Early life stress (ELS) has profound implications for developmental trajectories, yet the neural mechanisms underlying its long-term effects remain incompletely understood. In the present study, we examined whether interindividual similarity in ELS exposure aligns with similarity in neural representations and behavioral task performance in early adulthood. Leveraging a 20-year longitudinal dataset of Finnish families, we evaluated 87 young adults who underwent functional magnetic resonance imaging (fMRI) during an emotional go/no-go task. Intersubject representational similarity analysis (IS-RSA) was used to assess the associations between pairwise similarities in prospectively or retrospectively measured ELS, neural representations in 360 cortical regions, and task performance. We incorporated multidimensional scaling and Procrustes alignment to visualize interindividual differences in representational spaces. Prospective ELS, but not Retrospective ELS, was significantly associated with neural representational similarity across 40 cortical regions, including the anterior insula, frontal operculum, and anterior cingulate cortex. Higher Prospective ELS was also linked to reduced detection sensitivity, mediated by neural responses to angry facial expressions. These findings highlight the systematic and chronic effects of more moderate ELS on brain development and emphasize the value of prospective measurements and advanced similarity analyses in capturing the nuanced influences of ELS. By integrating spatial and shape analytical techniques, the present study provides new insights into the long-term neurobiological correlates of ELS and introduces novel methodological tools for neurodevelopmental research.

Voluntary locomotion induces an early and remote hemodynamic decrease in the large cerebral veins
SignificanceBehavior regulates dural and cerebral vessels, with spontaneous locomotion inducing dural vessel constriction and increasing stimulus-evoked cerebral hemodynamic responses. It is vital to investigate the function of different vascular network components, surrounding and within the brain, to better understand the role of the neurovascular unit in health and neurodegeneration.

AimWe characterized locomotion-induced hemodynamic responses across vascular compartments of the whisker barrel cortex: artery, vein, parenchyma, draining and meningeal vein.

ApproachUsing 2D-OIS, hemodynamic responses during locomotion were recorded in 9-12-month-old awake mice: wild-type, Alzheimers disease (AD), atherosclerosis or mixed (atherosclerosis/AD) models. Within somatosensory cortex, responses were taken from pial vessels inside the whisker barrel region ([WBR]: "whisker artery" and "whisker vein"), a large vein from the sagittal sinus adjacent to the WBR (draining vein), and meningeal vessels from the dura mater (which do not penetrate cortical tissue).

ResultsWe demonstrate that locomotion evokes an initial decrease in total hemoglobin (HbT) within the draining vein before the increase in HbT within WBR vessels. The locomotion event size influences the magnitude of the HbT increase in the pial vessels of the WBR, but not of the early HbT decrease within the draining veins. Following locomotion onset, an early HbT decrease was also observed in the overlying meningeal vessels, which unlike within the cortex did not go on to exceed baseline HbT levels during the remainder of the locomotion response. We show that locomotion-induced hemodynamic responses are altered in disease in the draining vein and whisker artery, suggesting this could be an important neurodegeneration biomarker.

ConclusionThis initial reduction in HbT within the draining and meningeal veins potentially serves as a space saving mechanism, allowing for large increases in cortical HbT associated with locomotion. Given this mechanism is impacted by disease it may provide an important target for vascular-based therapeutic interventions.

ARBEL: A Machine Learning Tool with Light-Based Image Analysis for Automatic Classification of 3D Pain Behaviors
A detailed analysis of pain-related behaviors in rodents is essential for exploring both the mechanisms of pain and evaluating analgesic efficacy. With the advancement of pose-estimation tools, automatic single-camera video animal behavior pipelines are growing and integrating rapidly into quantitative behavioral research. However, current existing algorithms do not consider an animals body-part contact intensity with- and distance from- the surface, a critical nuance for measuring certain pain-related responses like paw withdrawals ( flinching) with high accuracy and interpretability. Quantifying these bouts demands a high degree of attention to body part movement and currently relies on laborious and subjective human visual assessment. Here, we introduce a supervised machine learning algorithm, ARBEL: Automated Recognition of Behavior Enhanced with Light, that utilizes a combination of pose estimation together with a novel light-based analysis of body part pressure and distance from the surface, to automatically score pain-related behaviors in freely moving mice in three dimensions. We show the utility and accuracy of this algorithm for capturing a range of pain-related behavioral bouts using a bottom-up animal behavior platform, and its application for robust drug-screening. It allows for rapid objective pain behavior scoring over extended periods with high precision. This open-source algorithm is adaptable for detecting diverse behaviors across species and experimental platforms.

The VGCC auxiliary subunit α2δ1 is an extracellular GluA1 interactor and regulates LTP, spatial memory, and seizure susceptibility
Activity-dependent synaptic accumulation of AMPA receptors (AMPARs) and subsequent long-term synaptic strengthening underlie different forms of learning and memory. The AMPAR subunit GluA1 amino-terminal domain is essential for synaptic docking of AMPAR during LTP, but the precise mechanisms involved are not fully understood. Using unbiased proteomics, we identified the epilepsy and intellectual disability-associated VGCC auxiliary subunit 2{delta}1 as a candidate extracellular AMPAR slot. Presynaptic 2{delta}1 deletion in CA3 affects synaptic AMPAR incorporation during long-term potentiation, but not basal synaptic transmission, at CA1 synapses. Consistently, mice lacking 2{delta}1 in CA3 display a specific impairment in CA1-dependent spatial memory, but not in memory tests involving other cortical regions. Decreased seizure susceptibility in mice lacking 2{delta}1 in CA3 suggests a regulation of circuit excitability by 2{delta}1/AMPAR interactions. Our study sheds light on the regulation of activity-dependent AMPAR trafficking, and highlights the synaptic organizing roles of 2{delta}1.

Significance statementActivity-dependent accumulation of AMPA receptors (AMPARs) at excitatory synapses and subsequent synaptic strengthening underlies long-term potentiation (LTP), forms of learning and memory, and some epilepsies. The "slot model" posits that postsynaptic scaffolding contain "slots" for AMPAR complexes, and that increased synaptic activity augments the availability of slots to accommodate more receptors, thereby strengthening synapses and enabling LTP. The presence of the GluA1 AMPAR subunit amino-terminal domain (ATD) has recently emerged as an additional requirement for LTP. Here we identify the auxiliary voltage-gated calcium channel subunit 2{delta}1 as a GluA1 ATD interacting protein and provide evidence supporting a role for 2{delta}1 as an extracellular AMPAR slot regulating activity dependent synaptic AMPAR clustering, excitability, and cognitive function.

Reproducible Brain Entropy (BEN) Alterations During Rumination
Rumination, characterized by recurrent and repetitive thinking, is closely associated with mental disorders such as depression. However, the neural mechanisms underlying this mental state remain poorly understood. In this study, we use a relatively novel neuroimaging analysis method-Brain Entropy (BEN) to quantitatively assess the irregularity, disorder, and complexity of brain activity, providing new insights into the neural mechanisms of rumination.

We utilized a publicly available MRI dataset from three different scanners. The dataset included 41 healthy adult participants who completed identical fMRI tasks on IPCASGE, PKUGE, and PKUSIEMENS scanners. The time interval between the two visits was 22.0 {+/-} 14.6 days. The fMRI session included four runs: resting state, sad memory, rumination, and distraction. Whole brain voxel-wise BEN differences of task state and resting state, rumination and sad memory, distraction and sad memory, and rumination and distraction were tested and overlap regions after thresholded (p<0.05) across the three scanners were identified as exhibiting significant differences.

The results demonstrate distinct alterations in BEN across mental states. Compared to the sad memory condition, decreased BEN was found in the visual cortex (VC) during rumination and decreased BEN in the posterior cingulate cortex/precuneus (PCC/PCu) during distraction. However, when compared to distraction, rumination showed increased BEN in the PCC/PCu. These findings suggest that rumination involves heightened internal focus and reduced processing of external environmental information. This study highlights BEN as a valuable metric for elucidating the neural mechanisms underlying rumination and its role in depression.

Humans use overconfident estimates of auditory spatial and temporal uncertainty for perceptual inference
Making decisions based on noisy sensory information is a crucial function of the brain. Various decisions take each sensory signals uncertainty into account. Here, we investigated whether perceptual inferences rely on accurate estimates of sensory uncertainty. Participants completed a set of auditory, visual, and audiovisual spatial as well as temporal tasks. We fitted Bayesian observer models of each task to every participants complete dataset. Crucially, in some model variants the uncertainty estimates employed for perceptual inferences were independent of the actual uncertainty associated with the sensory signals. Model comparisons and analysis of the best-fitting parameters revealed that, in unimodal and bimodal contexts, participants perceptual decisions relied on overconfident estimates of auditory spatial and audiovisual temporal uncertainty. These findings challenge the ubiquitous assumption that human behavior optimally accounts for sensory uncertainty regardless of sensory domain.

Striatal Astrocytes Influence Dopamine Dynamics and Behavioral State Transitions
We demonstrate here that astrocytes in the striatum interact with striatal dopamine in bidirectional signaling with dopamine release actively driving surges in astrocytic Ca++, which in turn modulate and reduce subsequent dopamine release. These Ca++ surges accurately predict behavioral state changes from task-engaged to task-disengaged states, but fail to predict detailed action parameters. We propose that interactions between striatal astrocytes and dopamine are strong candidates to modulate nigro-striato-nigral loop function underlying on-going behavioral state dynamics.

How much is 'enough'? Considerations for functional connectivity reliability in pediatric naturalistic fMRI
functional connectivity (FC) measurements are important for robust and reproducible findings, yet pediatric functional magnetic resonance imaging (fMRI) faces unique challenges due to head motion and bias toward shorter scans. Passive viewing conditions during fMRI offer advantages for scanning pediatric populations, but FC reliability under these conditions remains underexplored. Here, we used precision fMRI data collected across three passive viewing conditions to directly compare FC reliability profiles between 25 pre-adolescent children and 25 adults, with each participant providing over 2.8 hours of data over four sessions. We found that FC test-retest correlations increased asymptotically with scan length, with children requiring nearly twice the post-censored scan time (24.6 minutes) compared to adults (14.4 minutes) to achieve comparable reliability, and that this effect was only partly attributable to head motion. Reliability differences between lower-motion adults and higher-motion children were spatially non-uniform and largest in ventral anterior temporal and frontal regions. While averaging features within functional networks improved intraclass correlation coefficient (ICC) reliability, values for higher-motion children remained in the poor-to-fair ICC range even with 48 minutes of total scan time. Viewing conditions with greater engagement reduced head motion in children but had lower FC reliability compared to less engaging low-demand videos, suggesting complex state- or condition-related trade-offs. These findings have important implications for developmental neuroimaging study design, particularly for higher motion pediatric populations.

Early-life adversity alters adult nucleus incertus neurons: implications for neuronal mechanisms of increased stress and compulsive behavior vulnerability
BACKGROUNDEarly-life stress (ELS) arising from physical and emotional abuse disrupts normal brain development and impairs hypothalamic-pituitary-adrenal axis function, increasing the risk of psychopathological disorders and compulsive behaviors in adulthood. However, the underlying neural mechanisms remain unclear. The brainstem nucleus incertus (NI) is a highly stress-sensitive locus, involved in behavioral activation and stress-induced reward (food/alcohol) seeking, but its sensitivity to ELS remains unexplored.

METHODSWe used neonatal maternal separation stress in rats as a model for ELS and examined its impact on stress-related mRNA and neuropeptide expression in the NI, using fluorescent in situ hybridization and immunohistochemistry, respectively. Using whole-cell, patch-clamp recordings we determined the influence of ELS on the synaptic activity, excitability, and electrophysiological properties of NI neurons. Using c-Fos protein expression we also assessed the impact of ELS on the sensitivity of NI neurons to acute restraint stress in adulthood.

RESULTSELS weakened the acute stress responsiveness of NI neurons, and caused dendritic shrinkage, impaired synaptic transmission and altered electrophysiological properties of NI neurons in a cell-type-specific manner. Additionally, ELS increased the expression of mRNA encoding corticotropin-releasing hormone receptor type 1 and the nerve-growth factor receptor, TrkA in adult NI.

CONCLUSIONSThe multiple, cell-type specific changes in the expression of neuropeptides and molecules associated with stress and substance abuse in the NI, as well as impairments in NI neuron morphology and electrophysiology caused by early-life stress and observed in the adult brain, may contribute to the increased susceptibility to stress and compulsive behaviors observed in individuals with a history of ELS.

RIG-I mediated neuron-specific IFN type 1 signaling in FUS-ALS induces neurodegeneration and offers new biomarker-driven individualized treatment options for (FUS-)ALS
Recent research has demonstrated significant aberrant activation of the innate immune system in ALS model systems due to mutations in SOD1, TARDBP and C9orf72 through stimulation of the TBK1-IRF3 pathway. This pathway can be activated, for example, by cGAS-STING-dependent sensing of cytosolic DNA that accumulates as a result of chronic DNA damage and defective mitochondria, both of which have been identified as early pathology in FUS-ALS spinal motor neurons (sMNs). Therefore, we analysed innate immune pathways in isogenic and non-isogenic FUSmut iPSC-derived sMNs, which revealed upregulation of interferon-stimulated genes (ISGs) and activation of the TBK1-IRF3 pathway in FUSmut sMNs. Notably, we found evidence for accumulation of cytosolic dsRNA and its sensor RIG-I in FUS-ALS. RIG-I, but not MDA5, was found to be significantly upregulated in FUSmut sMNs, and siRNA-mediated knockdown abolished the increased IFN1 activation in FUSmut sMNs. In post-mortem analysis, RIG-I was highly expressed in the remaining -MNs. IFN treatment of FUSwt sMNs phenocopied the axonal degeneration of FUSmut sMNs. Mechanistically, DNA damage induction did not increase ISG expression, but dsRNA was increased in the mitochondria of FUSmut sMNs. Mitochondrial transcription, a known source of dsRNA, was found to be upregulated in compartmental axonal RNAseq analysis and its inhibition reduced ISGs in FUS-ALS sMNs. Furthermore, the JAK-STAT inhibitor ruxolitinib alleviated the upregulated ISG expression and reversed the axonal degeneration of sMNs. Finally, we analysed ISG expression in peripheral blood samples from 18 FUS-ALS patients, eight of whom had a significantly elevated interferon signature. Blood ISGs correlated with disease progression rate and negatively with disease duration. RIG-I-mediated innate immune activation in sMNs may be an interesting novel individualised biomarker-driven therapeutic target in (FUS-) ALS.

A one-sentence summary of your paperRIG-I-I-mediated innate immune activation is found in FUS-ALS spinal motor neurons caused by cytosolic dsRNA accumulation due to mitochondrial transcriptional activation and is amenable to JAK-STAT inhibition and might thus be an interesting novel individualized biomarker-driven therapeutic approach in (FUS-) ALS

A signal of temporal integration in the human auditory brain: psychological insights, EEG evidence, and clinical application
Temporal integration, the process by which the auditory system combines sound information over a curtain period to form a coherent auditory object, is essential for coherent auditory perception, yet its neural mechanisms remain underexplored. We use a "transitional click train" paradigm, which concatenates two click trains with slightly differing inter-click intervals (ICIs), to investigate temporal integration in the human cortex. Using a 64-channel electroencephalogram (EEG), we recorded responses from 42 healthy participants exposed to regular and irregular transitional click trains and conducted change detection tasks. Regular transitional click trains elicited significant change responses in the human cortex, indicative of temporal integration, whereas irregular trains did not. These neural responses were modulated by ICI length, ICI contrast, and regularity. Behavioral data mirrored EEG findings, showing enhanced detection for regular conditions compared to irregular conditions and pure tones. Furthermore, variations in change responses were associated with decision-making processes. Temporal continuity was critical, as introducing gaps between click trains diminished both behavioral and neural responses. In clinical assessments, 22 coma patients exhibited diminished or absent change responses, effectively distinguishing them from healthy individuals. Our findings identify distinct neural markers of temporal integration and highlight the potential of transitional click trains for clinical diagnostics.

Environmental exposures and familial background alter the induction of neuropathology and inflammation after SARS-CoV-2 infection.
AbstractBasal ganglia disease has been reported as a post-infection sequela of several viruses, with documentation of this phenomenon from the H1N1 Spanish flu to the recent COVID-19 (SARS-CoV-2) pandemic. SARS-CoV-2 infection leads to multisystem deficits, including those affecting the nervous system. Here, we investigated whether a SARS-CoV-2 infection alone increases the susceptibility to develop parkinsonian phenotypes in C57BL/6J mice expressing the human ACE2 receptor, or in addition to two well-known toxin exposures, MPTP and paraquat. Additionally, we examined mice carrying a G2019S mutation in the LRRK2 gene. We also examined if vaccination with either an mRNA- or protein-based vaccine can alter any observed neuropathology. We find that the infection with the WA-1/2020 (alpha) or omicron B1.1.529 strains in ACE2 and G2019S LRRK2 mice both synergize with a subtoxic exposure to the mitochondrial toxin MPTP to induce neurodegeneration and neuroinflammation in the substantia nigra. This synergy appears toxin-dependent since we do not observe this following exposure to the direct redox-inducing compound paraquat. This synergistic neurodegeneration and neuroinflammation is rescued in WT mice that were vaccinated using either mRNA- and protein- based vaccines directed against the Spike protein of the SARS-CoV-2 virus. However, in the G2019S LRRK2 mutant mice, we find that only the protein-based vaccine but not the mRNA- based vaccine resulted in a rescue of the SARS-CoV-2 mediated neuropathology. Taken together, our results highlight the role of both environmental exposures and familial background on the development of parkinsonian pathology secondary to viral infection and the benefit of vaccines in reducing these risks.