bioRxiv Subject Collection: Neuroscience's Journal

Dynamic Predictive Spatial Encoding of Motor Intentions In Area V6A of the Posterior Parietal Cortex
To compute motor plans or intentions, the nervous system must translate target locations into body-centered coordinates. Visual stimuli, however, are sensed in retinotopic coordinates, which shift with eye movements. Furthermore, sensorimotor delays necessitate predictive processing. How does the brain compute timely gaze-invariant target locations? The dorsal visual pathway encodes spatial intentions, yet the underlying dynamic mechanisms remain elusive. Using multilevel analysis, we characterized intention coding in area V6A of the Posterior Parietal Cortex during delayed reaching tasks under diverse gaze-target conditions. We revealed a consistent population-level intention coding in V6A as eye positions changed. Next, we identified differential single-cell encoding of gaze and reaching targets in retinotopic, gaze-posture, and body-centered coordinates and elucidated the dynamical spatial normalization. Finally, we demonstrated context-dependent predictive spatial encoding in V6A, advancing our understanding of the temporal evolution of predictive visuomotor transformations during motor planning.

KHSRP-mediated Decay of Axonally Localized Prenyl-Cdc42 mRNA Slows Nerve Regeneration
The small GTPase CDC42 promotes axon growth through actin filament polymerization and this growth is driven by axonal localization of the mRNA encoding the prenylated CDC42 isoform (Prenyl-Cdc42). Here, we show that axonal Prenyl-Cdc42 mRNA transport and translation are decreased by growth-inhibiting stimulation and increased by growth-promoting stimulation. In contrast, axonal RhoA mRNA transport and translation are increased by growth inhibition but unaffected by growth promotion. Localized increase in KHSRP in response to growth inhibitory stimulation, through elevation of intracellular Ca2+, promotes decay of axonal Prenyl-Cdc42 mRNA. Distinct 3'UTR motifs regulate transport and stability of axonal Prenyl-Cdc42 mRNA. KHSRP protein binds to a Prenyl-Cdc42 mRNA motif within nt 801-875 and the mRNA is remarkably increased in axons of Khsrp-/- mice. Selective depletion of Prenyl-Cdc42 mRNA from axons reverses the accelerated axon regeneration seen in Khsrp-/- mice.

Testing the Vogt-Bailey Index using task-based fMRI across pulse sequence protocols
Local connectivity analyses in fMRI such as the Vogt-Bailey Index, investigate the prevalence of co-fluctuations in the time-series of adjacent voxels. While there have been in silico assessments of the VB Index, this technique has not yet been assessed in vivo. This study has two aims: first, to assess the VB Index using a task paradigm with well established a priori expectations on the brain region predominantly responsible for executing this task to determine whether the VB Index highlights this area. Second, we investigate if, and how, the spatial resolution of the sequence protocols employed, with their inherent effects on the signal-to-noise ratio, affect the resultant VB maps. A cohort of 10 research volunteers underwent fMRI acquisitions utilising a block design finger tapping experiment. Each volunteer was scanned with three sequence protocols, with all parameters equivalent except for the volume of the voxels. The resulting parametric maps derived using the VB Index were compared with those obtained from the conventional General Linear Model approach. Particular emphasis was placed on the identification of the hand portion of the motor homunculus. Across sequence protocols, the VB Index consistently identified elevated local connectivity in, qualitatively, the same portion of the motor cortex as that yielded by the General Linear Model based on the task paradigm. However, the VB Index also detected elevated local connectivity outside the motor cortex while the General Linear Model results were mostly restricted to the motor cortex. The consistently high VB Index, across sequence protocols, in the cortical region associated with an fMRI task paradigm, despite the approach's agnosticism to that task, provides support for the biological relevance of such local connectivity measures.

Effects of Interleukin-6 dysregulation in a mouse model of Alzheimer's disease: unraveling the complexity beyond amyloidosis
Interleukin-6 dysregulation has been implicated in the pathological progression of Alzheimer's disease (AD), a leading cause of dementia in the ageing population. Here we show that chronic neuroinflammation elicited by transgenic expression of IL-6 and systemic IL-6 deficiency influences the phenotype of the Tg2576 mouse model of AD, modulating mortality, body weight, behavioral and cognitive traits, amyloidosis, and neuroinflammation. While the conventional understanding of AD pathophysiology emphasizes the central role of Amyloid beta; peptides and amyloid plaques in the development and progression the disease, the absence of amyloidosis in the brain in a specific subset of Tg2576 mice challenges this notion. This suggests that several Tg2576-related traits may manifest independently of Amyloid beta, pointing to a potential contribution of alternative APP-related factors or pathways to the phenotypic alterations observed in Tg2576 mice. Together, our findings underscore the complexity of AD pathogenesis and emphasize the multifaceted nature of IL-6 in both physiological and neurodegenerative processes, particularly in the context of AD.

Divergence of Functional Brain Network Configurations in Same and Other Race Face Recognition
The "Other-Race Effect" (ORE) refers to the enhanced memory individuals have for faces within their own racial group compared to other races. This effect is attributed to limited exposure to different races and social-motivational factors affecting face processing. While past research has explored this effect through neuroimaging methods, the precise neural mechanisms that underlie the ORE remain a subject of ongoing investigation. Previous studies have largely adopted a modular perspective, concentrating on the differential activation of face-processing regions when comparing same-race and other-race facial recognition behaviors. However, given the multifaceted nature of the ORE, an exclusive focus on specialized regions may miss the pivotal role played by non-face-preferential brain areas in modulating this phenomenon. In the present study, we take a broader data-driven perspective using graph-theoretical techniques to investigate whole-brain network disparities in same- and other-race facial recognition. Our findings reveal a substantial impact of race on functional connectivity during face memorization. While other-race face recognition benefitted from higher local efficiency during encoding, reduced local efficiency was advantageous for memorization of same-race faces. Notably, successful other-race recognition was disproportionately supported by locally efficient processing in regions among the ventral and dorsal attention networks.

PI(3)P signaling regulates endosomal flux underlying developmental synaptic remodeling via Rab4
Rab4 GTPase, essential for endosomal sorting and trafficking, is implicated in synaptic atrophy and dementia. To uncover the underlying mechanism, we studied the correlation between Rab4 vesicle transport in axons and episodic remodeling of synapses in the central nervous system (CNS) of Drosophila larvae. We found that synapse-bound traffic and presynaptic enrichment of Rab4 vesicles increase during the programmed, transient contraction of synapses in the ventral neuropil region at a specific larval stage. This coincides with the episodic activation of insulin and Vps34-mediated signaling, which elevates phosphatidylinositol-3-phosphate levels on Rab4 vesicles. The presence of this phospholipid on Rab4-associated vesicles recruit a PX-domain-containing motor protein, Klp98A, accelerating synapse-directed traffic. This, in turn, increases presynaptic enrichment of Rab4 during the developmentally programmed synapse contraction phase. Our findings elucidate the molecular mechanism that regulates developmental synaptic plasticity in the CNS via insulin signaling and directed axonal transport of endosomes.

Loss of 5-HT2C Receptor Function Alters Motor Behavior and 5-HT2A Receptor Expression in Uninjured and Spinal Cord Injured Mice
Two subtypes of serotonin (5-HT) within the serotonin 2 class, the 5-HT2C receptor and the 5-HT2A receptor, are involved in the regulation of spinal motor function. The 5-HT2C receptor has been implicated in various aspects of volitional movement, such as locomotion, gait, coordination, and muscle contraction, as well as in involuntary motor behavior like spasms, which affect many individuals with spinal cord injury. Despite their known involvement in motor function, little is known about their physiological roles and the changes that occur after spinal cord injury. In this study, we have investigated the volitional and involuntary motor behavior of male and female uninjured and spinal cord injured knock-out mice that lack the functional 5-HT2C receptor by comparing these genetically manipulated mice to typical-functioning sex-matched wildtype mice. Behavioral assessments revealed differences in volitional muscle strength and coordination, as well as hyperreflexia, between the groups observed. Additionally, ex vivo sacral cord preparation data suggest that 5-HT2C receptor knock-out mice exhibit less spasm-like activity than wildtype mice, corroborating our results from behavioral testing in which the flexor withdrawal reflex of the hindlimbs was assessed. To investigate potential compensatory changes in 5-HT2C receptor and 5-HT2A receptor expression following spinal cord injury, western blot analysis was performed on lumbar and sacral spinal cord tissue from wildtype and 5-HT2C receptor knock-out mice before and after injury. Sex, genotype, and injury status significantly influenced 5-HT2C receptor and 5-HT2A receptor relative expression and distribution of these receptors in both spinal cord regions. Through a comprehensive approach combining behavioral assessments, electrophysiological experiments, and whole-tissue protein analysis, our findings provide strong evidence that the 5-HT2C receptor plays a critical role in both volitional motor function and involuntary motor behavior. Additionally, we identified significant differences in the regional distribution and relative expression of the 5-HT2C receptor and 5-HT2A receptor based on sex, genotype, and injury status.

Glutamatergic synaptic resilience to overexpressed human alpha-synuclein
Alpha synuclein (aSyn) is an abundant protein that, in the brain, is concentrated in neuronal presynaptic boutons and associates with synaptic vesicles. aSyn is strongly linked with Parkinson's disease (PD) due to its accumulation in pathognomonic inclusions in neuronal cells, including in glutamatergic neurons. While increased expression of wild-type (WT) aSyn due to multiplications of the SNCA gene, or the expression of mutant forms of aSyn, can cause familial forms of PD, it is still unclear whether increased levels of aSyn alone are sufficient to impair synaptic function. Previous studies have used experimental systems that do not allow systematic characterisation of presynaptic physiology. To address this gap in research, we used lentiviral vectors to overexpress human aSyn (haSyn) in continental and autaptic glutamatergic neurons from rodent hippocampus and systematically analysed their presynaptic function. Virally-transduced neurons exhibited levels of expression of haSyn that mimic those associated with triplications of the SNCA gene in PD patients (2-fold increase in total aSyn), as determined using quantitative immunofluorescence imaging and immunoblots. Neuronal toxicity, neuronal morphology, and SNAP-25, a presynaptic protein, were not altered in continental cultures. Finally, a systematic characterization of autaptic neurons expressing haSyn exhibited no significant difference in any parameter of synaptic function, including basal properties of evoked and spontaneous neurotransmitter release, and synaptic plasticity compared to neurons infected with a control virus. These results indicate that rodent glutamatergic neurons are resilient to aSyn overexpression. In conclusion, our findings suggest neurotoxicity associated with aSyn overexpression is not universal, and that a deeper understanding of aSyn biology and pathobiology is necessary.

Repeated application of bifocal transcranial alternating current stimulation (tACS) improves network connectivity and driving performance: a double-blind sham control study
Mounting evidence suggests that transcranial alternating current stimulation (tACS) can enhance response inhibition, a cognitive process crucial for sustained effort and decision-making. However, most prior studies have focused on within-session effects, with limited investigation into the effects of repeated applications, which are crucial for clinical applications. We examined the effects of repeated bifocal tACS targeting the right inferior frontal gyrus (rIFG) and pre-supplementary motor area (preSMA), regions implicated in response inhibition, on inhibitory control. We also explored changes to functional connectivity and whether this stimulation improved simulated driving performance. Thirty young adults (18-35 years) were assigned to either a sham or tACS group (20 Hz, 20 minutes), undergoing five stimulation sessions over two weeks. Resting-state electroencephalography (EEG) was used to assess functional connectivity between the preSMA and rIFG during the first and fifth bifocal tACS sessions and at a 7-day follow-up. Response inhibition was measured using a stop signal task (SST) administered throughout the sessions. Participants completed two simulated driving tasks (braking, general driving) before the first and after the final tACS intervention. Results revealed a significant improvement in functional connectivity in the tACS group across sessions, although no changes were observed in response inhibition and the braking task. Notably, general driving performance improved, with participants demonstrating closer adherence to the speed limit and greater spare attentional capacity. These findings highlight the potential of repeated bifocal tACS to enhance functional connectivity and related cognitive and motor processes, suggesting promising clinical applications for addressing issues related to cortical connectivity.

A reservoir model of respiration-induced perceptual alternation in binocular rivalry
Perceptual alternation in human binocular rivalry is more likely to occur during certain respiratory phases. In this paper, we show that the respiration dependence of perceptual alternations can be reproduced by a randomly connected recurrent neural network coupled with respiration relevant information via a neuromodulator of norepinephrine (NA). We considered two models of NA modulations; NA increases or decreases the nonlinearity of the activation function of neurons, and we found that the shape of the likelihood function of perceptual alternation depends only on respiratory phase, regardless of whether NA increases or decreases neural nonlinearity. Our results suggest that periodic neuromodulation facilitates the switching of competing neural states in specific phases and that this effect is independent of the excitatory or inhibitory effect of NA.

Context-specific interaction of the lipid regulator DIP-2 with phospholipid synthesis in axon regeneration and maintenance.
Neurons maintain their morphology over prolonged periods of adult life with limited regeneration after injury. C. elegans DIP-2 is a conserved regulator of lipid metabolism that affects axon maintenance and regeneration after injury. Here, we investigated genetic interactions of dip-2 with mutants in genes involved in lipid biosynthesis and identified roles of phospholipids in axon regrowth and maintenance. CEPT-2 and EPT-1 are enzymes catalyzing the final steps in the de novo phospholipid synthesis (Kennedy) pathway. Loss of function mutants of cept-2 or ept-1 show reduced axon regrowth and failure to maintain axon morphology. We demonstrate that CEPT-2 is cell-autonomously required to prevent age-related axonal defects. Interestingly, loss of function in dip-2 led to suppression of the axon regrowth phenotype observed in either cept-2 or ept-2 mutants, suggesting that DIP-2 acts to counterbalance phospholipid synthesis. Our findings reveal the genetic regulation of lipid metabolism to be critical for axon maintenance under injury and during aging.

OTULIN Interactome Reveals Immune Response and Autophagy Associated with Tauopathy in a Mouse Model
Tauopathies are neurodegenerative diseases that are pathologically characterized by accumulation of misfolded microtubule-associated protein tau aggregates in the brain. Deubiquitination, particularly by OTULIN, a unique deubiquitinase targeting methionine-1 (M1) linkages from linear ubiquitin chain assembly complex (LUBAC)), is reportedly associated with the accumulation of neurotoxic proteins in several neurodegenerative diseases, likely including tauopathies. To investigate the potential roles of OTULIN in tauopathies, we analyzed the OTULIN interactome in hippocampal tissues from PS19 transgenic (Tg) mice and their non-transgenic (nTg) littermate controls using affinity purification-mass spectrometry (AP-MS). We identified 705 and 800 proteins enriched in Tg and nTg samples, respectively, with a protein false discovery rate (FDR) of <1%. Of these, 189 and 205 proteins were classified as probable OTULIN interactors in Tg and nTg groups, respectively, based on Significance Analysis of INTeractome (SAINT) score of [≥]0.80 and FDR of [≤] 5%. A total of 84 proteins were identified as OTULIN interactors in the PS19 Tg group, while 100 proteins were associated with OTULIN in the nTg controls. Functional enrichment analyses revealed that OTULIN-interacting proteins in the nTg group were enriched in pathways related to spliceosome, complement and coagulation cascades, and ribosome, whereas those in the Tg group were associated with immune response and autophagy. These findings suggest that OTULIN-interacting proteins may play a critical role in the pathogenesis of tauopathy in this mouse model.

Multiplexed CRISPRi Reveals a Transcriptional Switch Between KLF Activators and Repressors in the Maturing Neocortex
A critical phase of mammalian brain development takes place after birth. Neurons of the mouse neocortex undergo dramatic changes in their morphology, physiology, and synaptic connections during the first postnatal month, while properties of immature neurons, such as the capacity for robust axon outgrowth, are lost. The genetic and epigenetic programs controlling prenatal development are well studied, but our understanding of the transcriptional mechanisms that regulate postnatal neuronal maturation is comparatively lacking. By integrating chromatin accessibility and gene expression data from two subtypes of neocortical pyramidal neurons in the neonatal and maturing brain, we predicted a role for the Kruppel-Like Factor (KLF) family of Transcription Factors in the developmental regulation of neonatally expressed genes. Using a multiplexed CRISPR Interference (CRISPRi) knockdown strategy, we found that a shift in expression from KLF activators (Klf6, Klf7) to repressors (Klf9, Klf13) during early postnatal development functions as a transcriptional switch to first activate, then repress a set of shared targets with cytoskeletal functions including Tubb2b and Dpysl3. We demonstrate that this switch is buffered by redundancy between KLF paralogs, which our multiplexed CRISPRi strategy is equipped to overcome and study. Our results indicate that competition between activators and repressors within the KLF family regulates a conserved component of the postnatal maturation program that may underlie the loss of intrinsic axon growth in maturing neurons. This could facilitate the transition from axon growth to synaptic refinement required to stabilize mature circuits.

Functional Connectivity Shapes Spine Stability in the Hippocampus
Synaptic connections between neurons determine the flow of information in the brain. Changes in synaptic weight, along with synapse formation and pruning, reshape the functional connectivity of neural circuits - key mechanisms underlying learning and memory. However, the relationship between functional strength and the structural dynamics of individual glutamatergic synapses in the living mammalian brain remains poorly understood. Specifically, how spine morphology and stability relate to functional adaptations is unclear. Here, we repeatedly recorded excitatory postsynaptic calcium transients in single postsynaptic spines of CA1 neurons in response to optogenetic stimulation of presynaptic CA3 cells in awake, head-fixed mice for over 2 weeks. We found that functional connectivity predicted both the structural stability and clustering of synaptic inputs. Spines with large responses exhibited larger volume and higher stability compared to non-responding spines. Over time, responses were highly variable at individual synapses, but stable at the dendritic level, suggesting that dendritic branches receive stable input despite large fluctuations at individual synapses.

Optogenetic restoration of neuron subtype-specific cortical activity ameliorates motor deficits in Huntington's Disease mice
Huntington's disease (HD) is a devastating movement disorder without a current cure. Although the monogenic basis of HD is well-defined, the complex downstream effects that underlie behavioral symptoms are poorly understood. These effects include cortical dysfunctions, yet the role of specific cortical neuronal subtypes in HD symptoms remain largely unexplored. Here, we used longitudinal in vivo two-photon calcium imaging to examine the activity of two cortical inhibitory neuron (IN) subtypes and excitatory corticostriatal projection neurons (CSPNs) in the motor cortex of R6/2 HD mouse model throughout disease progression. We found that motor deficits in R6/2 mice were accompanied by neuron type-specific abnormalities in movement-related activity, including hypoactivity of vasoactive intestinal peptide (VIP)-INs and CSPNs. Optogenetic activation of VIP-INs in R6/2 mice restored healthy levels of activity in VIP-INs and their downstream CSPNs and ameliorated motor deficits in R6/2 mice. Our findings highlight cortical INs as a potential therapeutic target for HD and possibly other neurological diseases.

miR-124 acts during Drosophila development to determine the phase of adult circadian behavior
Circadian behaviors need to be properly phased with the day/night cycle to be beneficial. We previously showed that the microRNA miR-124 regulates circadian behavior phase in Drosophila. Here, we report that miR-124 expression during larval development is required for proper phasing of both morning and evening peaks of activity in adults. Loss of miR-124 results in significant miswiring within the circadian neural network and severely alters neural activity rhythms in the ventral Lateral Neurons (s-LNvs) and the posterior Dorsal Neurons 1 (DN1ps), which control the timing of morning and evening activity. Silencing the s-LNvs in miR-124 mutant flies restores the phase of evening activity, while activating the DN1ps rescues the phases of both morning and evening activities. Our findings thus reveal the pivotal role of miR-124 in sculpting the circadian neural network during development and its long-lasting impact on circuit activity and adult circadian behavior.

Xylazine potentiates the interoceptive effects of fentanyl in male and female rats
Rationale: Xylazine, a sedative typically used in veterinary medicine, has been increasingly detected as an adulterant in the unregulated opioid supply and present in opioid overdose deaths. Therefore, xylazine-adulterated fentanyl is a growing public health concern. People who use drugs have reported that xylazine changes and prolongs the effects of fentanyl. Objectives: We used standard operant drug discrimination procedures to better understand how xylazine impacts the discriminative stimulus/interoceptive effects of fentanyl. Methods: Male and female Long-Evans rats (n=23) were trained to discriminate fentanyl (0.032 mg/kg intraperitoneal) such that one lever was reinforced with sucrose on days when fentanyl was administered, and the other lever was reinforced when vehicle was administered. Once rats met testing criteria, we tested a dose range of fentanyl to confirm discriminative stimulus control, then we tested if xylazine alone produced fentanyl-like effects and if the addition of xylazine to fentanyl impacted fentanyl interoceptive effects. Results: Stimulus control was confirmed, as rats showed increased percent responses on the fentanyl-appropriate lever as well as decreased response rates for increasing doses of fentanyl. Xylazine alone did not substitute for the stimulus effects of fentanyl but produced similar response rate reductions as fentanyl alone. Xylazine co-administered with fentanyl potentiated the stimulus effects of lower doses of fentanyl in both males and females and potentiated response rate reductions. Conclusions: These results indicate that xylazine enhances the interoceptive effects of fentanyl, which may inform clinical research about xylazine-adulterated fentanyl.

Motion processing in visual cortex of maculopathy patients
Previous studies on animal models suggested that visual areas involved in motion processing could undergo important cortical reorganizations following retinal damages. This could have major implications for patients suffering from macular degeneration (MD), the leading cause of vision loss in older adults. Here, we performed fMRI recordings in a group of maculopathy patients (including individuals suffering from age-related macular degeneration or from Stargardt's Disease) and a control group to characterize the motion processing cortical network in MD patients and determine whether this network undergoes significant large-scale reorganisations following the onset of the scotoma. We used an experimental protocol based on random-dot kinematograms (RDKs) classically employed to characterize motion-selective areas in the brain. To ensure that the visual information processed by the two groups was equivalent, the visual field in each control participant was masked using an artificial scotoma directly derived from clinical measurements in their paired patient. We found that in MD patients, translational motion elicited significant and robust activations in a restricted cortical network which included the human V5/MT+ complex (hMT+), areas V3A and V6 and a portion of primary visual areas (V1, V2 and V3) connected to peripheral vision. Importantly, the same patterns of responses were also observed in control participants. Moreover, the extent and strength of activation within these motion-selective areas did not differ significantly between the two groups. Altogether, these results suggest that in humans, the motion-selective network does not undergo significant large-scale cortical reorganizations following the onset of MD.

Cortical astrocyte activation triggers meningeal nociception and migraine-like pain
Although migraine attacks are considered to arise in the brain, the exact mechanisms by which the brain can generate migraine pain remain unclear. Visual cortex hyperexcitability has been observed consistently across different migraine subtypes. During cortical hyperexcitability events, aberrant neurotransmitter release drives heightened G-coupled receptor signaling in cortical astrocytes, which in turn release gliotransmitters and other factors with algesic properties. This study investigated whether heightened activation of cortical astrocytes Gq-coupled signaling is sufficient to drive peripheral meningeal nociceptive responses linked to the generation of migraine headaches. Using a rat model, we employed an AAV-based chemogenetic approach that allows selective activation of visual cortex astrocyte Gq-GPCR signaling. We combined this chemogenetic approach with in vivo single-unit recording of trigeminal meningeal nociceptors to assess changes in their ongoing activity and mechanosensitivity. We further used behavioral testing of migraine-like behaviors and pharmacological targeting of calcitonin gene-related peptide (CGRP), using a monoclonal antibody (anti-CGRP mAb) to further assess the relevance of cortical astrocyte activation to migraine. We discovered that heightened activation of Gq-coupled signaling in visual cortex astrocytes drives persistent discharge and increased mechanosensitivity of trigeminal nociceptors innervating the meninges overlying the visual cortex. Cortical astrocytic activation also generated cephalic mechanical pain hypersensitivity, reduced exploratory behavior, and anxiety-like behaviors linked to migraine headaches. Targeting calcitonin gene-related peptide signaling, implicated in migraine pathophysiology, using a monoclonal antibody effectively suppressed astrocyte-mediated meningeal nociceptor discharge and alleviated migraine-related behaviors. Our findings reveal a previously unappreciated role for augmented visual cortex astrocyte signaling as a triggering factor sufficient to generate meningeal nociception and migraine pain and greatly expand our understanding of migraine pathophysiology.

Cocaine extended access gates compulsive-like seeking in rats
When does compulsive-like drug seeking emerge? Despite decades of research, and critical advances in our understanding of brain processes leading to addiction, this question remains widely unanswered. So far, behavioral models assessing compulsive-like cocaine seeking following an extended access to cocaine failed to capture the development of its compulsive seeking. In fact, compulsive-like animals immediately displayed pathological seeking when facing its negative consequences of drug seeking, usually materialized by an unescapable mild electric shock on the paws. Here, we designed a new task, "Punished Seeking during Extended access" (PSE), by inserting punished seeking trials within the sessions of extended access to cocaine. We show that compulsive-like cocaine seeking progressively emerges after several PSE sessions, once cocaine intake has been escalated. We thus provide the addiction community a pertinent model to explore brain mechanisms sustaining the emergence of compulsive-like cocaine seeking.

Chronically implantable μLED arrays for optogenetic cortical surface stimulation in mice
Cortical implants are a proven clinical neurotechnology with the potential to transform our understanding of cognitive processes. These processes rely on complex neuronal networks that are difficult to selectively probe or stimulate. Optogenetics offers cell-type specificity, but achieving the density and coverage required for chronic, high-resolution modulation remains a challenge. Here we present a 100-element LED array (200 m pixel pitch, 2 x 2 mm2 footprint) coupled into a miniaturised, flexible system suitable for chronic implantation and optogenetic stimulation of the surface of the mouse cortex. The LEDs can remain stable for over 300 hours continuous operation time in-vivo, allowing for months-long chronic experiments. Simultaneous electrophysiology recordings confirmed robust neuronal responses corresponding to low LED drive currents (<5 mA), minimising thermal effects and supporting future wireless operation. The spatial resolution of neuronal responses was consistent with a simulated model of light scattering in the cortical layers, enabling device optimisation. Behavioural experiments with chronically implanted mice demonstrated robust learning during discrimination tasks using spatially distinct optogenetic stimulation patterns.

DMT-induced shifts in criticality correlate with ego-dissolution
Psychedelics profoundly alter subjective experience and brain dynamics. Brain oscillations express signatures of near-critical dynamics, relevant for healthy function. Alterations in the proximity to criticality have been suggested to underlie the experiential and neurological effects of psychedelics. Here, we investigate the effects of a psychedelic substance (DMT) on the criticality of brain oscillations, and in relation to subjective experience. We find that DMT shifts the dynamics of brain oscillations away from criticality in alpha and adjacent frequency bands. In this context, entropy is increased while complexity is reduced. We find that the criticality shifts observed in alpha and theta bands correlate with the intensity ratings of ego-dissolution, a hallmark of psychedelic experience. Finally, using a recently developed metric, the functional excitatory-inhibitory ratio, we find that the DMT-induced criticality shift in brain oscillations is towards subcritical regimes. These findings have major implications for the understanding of psychedelic mechanisms of action in the human brain and for the neurological basis of altered states of consciousness.

Optogenetic interrogation of the lateral-line sensory system reveals mechanisms of pattern separation in the zebrafish brain
The ability of animals to interact with their environment hinges on the brain's capacity to distinguish between patterns of sensory information and accurately attribute them to specific sensory organs. The mechanisms by which neuronal circuits discriminate and encode the source of sensory signals remain elusive. To address this, we utilized as a model the posterior lateral line system of larval zebrafish, which is used to detect water currents. This system comprises a series of mechanosensory organs called neuromasts, which are innervated by neurons from the posterior lateral line ganglion. By combining single-neuromast optogenetic stimulation with whole-brain calcium imaging, we developed a novel approach to investigate how inputs from neuromasts are processed. Upon stimulating individual neuromasts, we observed that neurons in the brain of the zebrafish show diverse selectivity properties despite a lack of topographic organization in second-order circuits. We further demonstrated that complex combinations of neuromast stimulation are represented by sparse ensembles of neurons within the medial octavolateralis nucleus (MON) and found that neuromast input can be integrated nonlinearly. Our approach offers an innovative method for spatiotemporally interrogating the zebrafish lateral line system and presents a valuable model for studying whole-brain sensory encoding.

Bridge protein-mediated viral targeting of cells expressing endogenous μ-opioid G protein-coupled receptors in the mouse and monkey brain
Targeting specific cell types is essential for understanding their functional roles in the brain. Although genetic approaches enable cell-type-specific targeting in animals, their application to higher mammalian species, such as nonhuman primates, remains challenging. Here, we developed a nontransgenic method using bridge proteins to direct viral vectors to cells endogenously expressing -opioid receptors (MORs), a G protein-coupled receptor. The bridge protein comprises the avian viral receptor TVB, the MOR ligand {beta}-endorphin ({beta}ed), and an interdomain linker. EnvB-enveloped viruses bind to the TVB component, followed by the interaction of {beta}ed with MORs, triggering viral infection in MOR-expressing cells. We optimized the secretion signals, domain configurations, and interdomain linkers of the bridge proteins to maximize viral targeting efficiency and specificity. Alternative configurations incorporating different ligands and viral receptors also induced viral infection in MOR-expressing cells. The optimized {beta}ed-f2-TVB bridge protein with EnvB-pseudotyped lentiviruses induced infection in MOR-expressing cells in the striatum of mice and monkeys. An intersectional approach combining {beta}ed-f2-TVB with a neuron-specific promoter refined cell-type specificity. This study establishes the foundation for the rational bridge protein design and the feasibility of targeting G protein-coupled receptors beyond tyrosine kinase receptors, thereby expanding targetable cell types in the brain and throughout the body.

Synergistic MAPT mutations as a platform to uncover modifiers of tau pathogenesis
The natively unfolded tau protein is extremely soluble, which poses challenges when modeling neurofibrillary tangle (NFT) pathology in Alzheimers disease (AD). To overcome this hurdle, we combined P301L and S320F mutations (PL-SF) to generate a rapid and reliable platform to expedite the discovery of factors that modulate tau aggregation. Using this model, we evaluated heat-shock proteins (Hsp), traditionally linked to tau pathology, but whose role in AD remains enigmatic and controversial. In primary neurons, expression of Hsp70, but not Hsc70 or Hsp90, exacerbated tau aggregation. Conversely, lowering of Hsp70 by shRNA or a chaperone-deficient tau mutant (PL-SF-4delta) reduced tau phosphorylation and abrogated tau aggregation, highlighting Hsp70 as a key driver of tau aggregation. Functionally, mature aggregate-bearing neurons showed deficits in neuronal firing and network communication, while chaperone-binding deficient tau variants displayed reduced tau pathology and restored network properties. This study provides a powerful cell intrinsic model for accelerated tau aggregation, which can be harnessed to identify regulators of tau aggregation as promising therapeutic targets.

Computation-through-Dynamics Benchmark: Simulated datasets and quality metrics for dynamical models of neural activity
A primary goal of systems neuroscience is to discover how ensembles of neurons transform inputs into goal-directed behavior, a process known as neural computation. A powerful framework for understanding neural computation uses neural dynamics - the rules that describe the temporal evolution of neural activity - to explain how goal-directed input-output transformations occur. As dynamical rules are not directly observable, we need computational models that can infer neural dynamics from recorded neural activity. We typically validate such models using synthetic datasets with known ground-truth dynamics, but unfortunately existing synthetic datasets don not reflect fundamental features of neural computation and are thus poor proxies for neural systems. Further, the field lacks validated metrics for quantifying the accuracy of the dynamics inferred by models. The Computation-through-Dynamics Benchmark (CtDB) fills these critical gaps by providing: 1) synthetic datasets that reflect computational properties of biological neural circuits, 2) interpretable metrics for quantifying model performance, and 3) a standardized pipeline for training and evaluating models with or without known external inputs. In this manuscript, we demonstrate how CtDB can help guide the development, tuning, and troubleshooting of neural dynamics models. In summary, CtDB provides a critical platform for model developers to better understand and characterize neural computation through the lens of dynamics.

An integrative model of AMPA receptor trafficking reveals the central contribution of local translation in subtype-specific kinetics
AMPA-type glutamate receptors (AMPARs) underlie most of the excitatory synaptic transmission in the brain and are crucial for implementing long-term synaptic plasticity. AMPARs are multi-protein complexes composed of two types of subunits: pore-forming subunits GluA1-4 that assemble in the endoplasmic reticulum and form the glutamate-gated ion channel, and auxiliary subunits that modulate receptor biophysical properties and mediate their forward trafficking to the plasma membrane. Here, using a combination of theoretical and experimental approaches, we elucidate the kinetics of essential trafficking steps and the protein sources necessary to explain the experimentally observed distribution of AMPARs and the response of different AMPAR subtypes to LTP induction. Our data indicate that the mRNA coding for one of the most abundant AMPAR auxiliary subunits, CNIH-2, is abundant in dendrites. Consistent with this mRNA distribution, CNIH-2 is locally synthesized. In contrast, the pore-forming subunits GluA1 and GluA2 are mostly synthesized in the cell body. CNIH-2 synthesis increases after the (chemical) induction of long-term potentiation. Strikingly, the translation of CNIH-2 is required for the plasma membrane insertion of GluA2-containing receptors and not GluA1-homomeric AMPARs. Using the selective trafficking of GluA2-containing AMPARs by CNIH-2, our computational model can explain the distinct temporal profiles in response to plasticity induction of two major subtypes of AMPARs, the slow-response of the calcium impermeable (GluA2-containing) and fast kinetics of the calcium-permeable (GluA2-lacking) AMPARs.

A genetically-diverse mouse model reveals a complex gene-environment regulation of cognitive resilience and susceptibility to Alzheimer disease
Alzheimer disease (AD) has a complex etiology arising from largely unknown interactions between genetic and environmental factors. Even in populations with highly penetrant, disease-causing familial AD mutations, there is wide variation in disease onset and progression, suggesting that clinical symptoms are modified by genetics and environment. Identification of such modifiers is critical, as mechanisms that promote resilience to deleterious AD mutations, unhealthy diet, or aging represent promising therapeutic targets for AD and other causes of cognitive decline; global resilience factors that protect against multiple hits are among the highest priority for discovery. Both genetic and environmental protective factors in AD have been identified; however, interacting gene-environment (GxE) factors are incredibly difficult to study in human populations given complex genomes, poor self-reporting, data from underrepresented groups, and incompletely documented exposomes. Here, we used a population of mouse strains that model the polygenic nature of human AD to characterize individuals that display cognitive resilience to high-risk genetic and dietary perturbations to define and quantitate roles for genetics, sex, age, diet, and complex interactions that are nearly impossible to elucidate from humans or inbred AD mice. We found that some strains showed improved AD-related outcomes when fed a high-fat high-sugar (HFHS) diet, suggesting the need for personalized recommendations for dietary interventions in AD. Cognitive resilience is polygenetic; however, we found a locus on Chr 10 that was suggestively associated with cognitive resilience to AD in females, and this association was strengthened by HFHS diet, directly pointing to an interaction between specific genetic and environmental factors in AD risk and resilience. In conclusion, this study is the first of its kind to explore characteristics of resilience and GxE interactions in a genetically diverse mouse model. We present a subset of strains that exemplify global cognitive resilience to be leveraged for deep mechanistic studies aimed toward development of resilience-based and personalized therapeutic interventions.

Vagus nerve stimulation modulates information representation of sustained activity in layer specific manner in the rat auditory cortex
It will contribute to the development of sustainable artificial intelligence to elucidate the mechanism of neural modulation by which the brain of a living organism enable stable information processing in response to constantly changing external environments and internal states. As one of such cortical modulation, the present study focused on the effect of vagus nerve stimulation (VNS) therapy on information representation of the auditory cortex. By quantifying sound representation using machine learning, we investigated whether VNS alters cortical information representation in a layer-specific and frequency band-specific manner. A microelectrode array meticulously mapped the band-specific power and phase-locking value of sustained activities in every layer of the rat auditory cortex. Sparse logistic regression was used to decode the test frequency from these neural characteristics. The comparison of decoding accuracy before and after the application of VNS indicated that sound representation of the high-gamma band activity was impaired in the deeper layers, i.e., layers 5 and 6, while it was slightly improved in the superficial layers, i.e., layers 2, 3, and 4. Moreover, there was an improvement of sound representation in theta band activity in the deeper layers, demonstrating the layer-specific and frequency band-specific effect of VNS. Given that the cortical laminar structure and oscillatory activity in multiple frequency bands helps the auditory cortex to act as a hub for feed-forward and feed-back pathways in various information processing, the current findings support the possibility that VNS provide complex effects on brain function by altering the balance of cortical activity between layers and frequency bands.

Complementary MR measures of white matter and their relation to cardiovascular health and cognition
Magnetic Resonance Imaging (MRI) offers many ways to non-invasively estimate the properties of white matter (WM) in the brain. In addition to the various metrics derived from diffusion-weighted MRI, one can estimate total WM volume from T1-weighted MRI, WM hyper-intensities from T2-weighted MRI, myelination from the T1:T2 ratio, or from the magnetisation-transfer ratio (MTR). Here we utilise the presence of all of these MR contrasts in a population based life-span cohort of 650 healthy adults [CamCAN cohort] to identify the latent factors underlying the covariance of 11 commonly-used WM metrics. Four factors were needed to explain 89% of the variance, which we interpreted in terms of 1) fibre density / myelination, 2) free-water / tissue damage, 3) fibre-crossing complexity and 4) microstructural complexity. These factors showed distinct effects of age and sex. To test the validity of these factors, we related them to measures of cardiovascular health and cognitive performance. Specifically, we ran path analyses 1) linking cardio-vascular measures to the WM factors, given the idea that WM health is related to cardiovascular health, and 2) linking the WM factors to cognitive measure, given the idea that WM health is important for cognition. Even after adjusting for age, we found that a vascular factor related to pulse pressure predicted the WM factor capturing free-water / tissue damage, and that several WM factors made unique predictions for fluid intelligence and processing speed. Our results show that there is both complementary and redundant information across common MR measures of WM, and their underlying latent factors may be useful for pinpointing the differential causes and contributions of white matter health in healthy aging.