bioRxiv Subject Collection: Neuroscience's Journal

Longitudinal neuromelanin changes in prodromal and early Parkinson's disease in humans and rat model
Studies in animal models of Parkinson's disease (PD) suggested that the accumulation of the neuromelanin (NM), a pigment contained in nigral dopaminergic neurons, could trigger neurodegeneration above a pathogenic threshold. Here we investigated this hypothesis using NM-sensitive MRI in rodents and in patients with isolated rapid eye movement sleep disorders (iRBD) subjects, a prodromal phase of parkinsonism, and early PD. We first combined NM-sensitive MRI and histology to study NM accumulation and neurodegeneration in a humanized rat model of PD. NM-MRI signal changes were biphasic with an initial increase due to the accumulation of NM in dopaminergic neurons, followed signal decrease due to neurodegeneration. In healthy subjects and patients with iRBD, NM-MRI signal increased initially and then decreased similarly as in rodents after reaching a similar maximum signal intensity in both groups. In early PD and converted iRBD patients, NM-MRI signal drop was greater than in healthy individuals. Results in animals and humans show that NM-sensitive MRI is a marker of the intracellular NM accumulation up to a threshold then of neuronal degeneration beyond this threshold and agree with the hypothesis of a pathogenic threshold of NM triggering neurodegeneration.

A Transcriptional Signature of Induced Neurons Differentiates Virologically Suppressed People Living With HIV from People Without HIV
Neurocognitive impairment is a prevalent and important co-morbidity in virologically suppressed people living with HIV (PLWH), yet the underlying mechanisms remain elusive and treatments lacking. Here, we explored for the first time, use of participant-derived directly induced neurons (iNs) to model neuronal biology and injury in PLWH. iNs retain age- and disease-related features of the donors, providing unique opportunities to reveal novel aspects of neurological disorders. We obtained primary dermal fibroblasts from six virologically suppressed PLWH (range: 27 - 64 years, median: 53); 83% Male; 50% White) and seven matched people without HIV (PWOH) (range: 27 - 66, median: 55); 71% Male; 57% White). iNs were generated using transcription factors NGN2 and ASCL1, and validated by immunocytochemistry and single-cell-RNAseq. Transcriptomic analysis using bulk-RNAseq identified 29 significantly differentially expressed genes between iNs from PLWH and PWOH. Of these, 16 genes were downregulated and 13 upregulated in PLWH iNs. Protein-protein interaction network mapping indicates that iNs from PLWH exhibit differences in extracellular matrix organization and synaptic transmission. IFI27 was upregulated in iNs from PLWH, which complements independent post-mortem studies demonstrating elevated IFI27 expression in PLWH-derived brain tissue, indicating that iN generation reconstitutes this pathway. Finally, we observed that expression of the FOXL2NB-FOXL2-LINC01391 genome locus is reduced in iNs from PLWH and negatively correlates with neurocognitive impairment. Thus, we have identified an iN gene signature of HIV through direct reprogramming of skin fibroblasts into neurons revealing novel mechanisms of neurocognitive impairment in PLWH.

Myeloid-derived β-hexosaminidase is essential for neuronal health and lysosome function: implications for Sandhoff disease
Lysosomal storage disorders (LSDs) are a large disease class involving lysosomal dysfunction, often resulting in neurodegeneration. Sandhoff disease (SD) is an LSD caused by a deficiency in the {beta} subunit of the {beta}-hexosaminidase enzyme (Hexb). Although Hexb expression in the brain is specific to microglia, SD primarily affects neurons. To understand how a microglial gene is involved in maintaining neuronal homeostasis, we demonstrated that {beta}-hexosaminidase is secreted by microglia and integrated into the neuronal lysosomal compartment. To assess therapeutic relevance, we treated SD mice with bone marrow transplant and colony stimulating factor 1 receptor inhibition, which broadly replaced Hexb-/- microglia with Hexb-sufficient cells. This intervention reversed apoptotic gene signatures, improved behavior, restored enzymatic activity and Hexb expression, ameliorated substrate accumulation, and normalized neuronal lysosomal phenotypes. These results underscore the critical role of myeloid-derived {beta}-hexosaminidase in neuronal lysosomal function and establish microglial replacement as a potential LSD therapy.

Dysregulated balance of D- and L-amino acids modulating glutamatergic neurotransmission in severe spinal muscular atrophy.
Spinal muscular atrophy (SMA) is a neuromuscular disorder caused by reduced expression of the survival motor neuron (SMN) protein. In addition to motor neuron survival, SMN deficiency affects the integrity and function of afferent synapses that provide glutamatergic excitatory drive essential for motor neuron firing and muscle contraction. However, it is unknown whether deficits in the metabolism of excitatory amino acids and their precursors contribute to neuronal dysfunction in SMA. To address this issue, we measured the levels of the main neuroactive D- and L-amino acids acting on glutamatergic receptors in the central nervous system of SMNdelta7 mice as well as the cerebrospinal fluid (CSF) of SMA patients of varying severity before and after treatment with the SMN-inducing drug Nusinersen. Our findings reveal that SMN deficiency disrupts glutamate and serine metabolism in the CSF of severe SMA patients, including decreased concentration of L-glutamate, which is partially corrected by Nusinersen therapy. Moreover, we identify dysregulated L-glutamine to L-glutamate conversion as a shared neurochemical signature of altered glutamatergic synapse metabolism that implicates astrocyte dysfunction in both severe SMA patients and mouse models. Lastly, consistent with a correlation of higher CSF levels of D-serine with better motor function in severe SMA patients, we show that daily supplementation with the NMDA receptor co-agonist D-serine improves neurological deficits in SMNdelta7 mice. Altogether, these findings provide direct evidence for dysregulation of D- and L-amino acid metabolism linked to glutamatergic neurotransmission in severe SMA and have potential implications for treating this neurological disorder.

Linearizing and forecasting: a reservoir computing route to digital twins of the brain
Exploring the dynamics of a complex system, such as the human brain, poses significant challenges due to inherent uncertainties and limited data. In this study, we enhance the capabilities of noisy linear recurrent neural networks (lRNNs) within the reservoir computing framework, demonstrating their effectiveness in creating autonomous in silico replicas - digital twins - of brain activity. Our findings reveal that the poles of the Laplace transform of high-dimensional inferred lRNNs are directly linked to the spectral properties of observed systems and to the kernels of auto-regressive models. Applying this theoretical framework to resting-state fMRI, we successfully predict and decompose BOLD signals into spatiotemporal modes of a low-dimensional latent state space confined around a single equilibrium point. lRNNs provide an interpretable proxy for clustering among subjects and different brain areas. This adaptable digital-twin framework not only enables virtual experiments but also offers computational efficiency for real-time learning, highlighting its potential for personalized medicine and intervention strategies.

Control of spatiotemporal activation of organ-specific fibers in the vagus nerve by intermittent interferential current stimulation
Vagus nerve stimulation (VNS) is emerging as potential treatment for several chronic diseases, however, limited control of fiber activation to promote desired effects over side effects restricts clinical translation. Here we describe a new VNS method that relies on intermittent, interferential sinusoidal current stimulation (i2CS) through implanted, multi-contact epineural cuffs. In swine, i2CS elicits specific nerve potentials and end organ responses, distinct from equivalent non-interferential sinusoidal stimulation. Comparing experimental results with anatomical trajectories of nerve fascicles from end organs to the stimulation electrode indicates that i2CS activates organ-specific fascicles rather than the entire nerve. Experimental results and anatomically realistic, physiologically validated biophysical models of the vagus nerve demonstrate that i2CS reduces fiber activation at the focus of interference. Current steering and repetition frequency determine spatiotemporal pattern of vagal fiber activation, allowing tunable and precise control of neural and organ responses. In experiments in a cohort of anesthetized swine, i2CS has improved selectivity for a desired effect, mediated by smaller bronchopulmonary fibers, over a side effect, mediated by larger laryngeal fibers, compared to non-interferential sinusoidal or square pulse VNS.

Maintenance of Bound or Independent Features in Visual Working Memory is Taskdependent
Conflicting findings exist regarding whether features of an object are stored separately or bound together in visual working memory. This controversy is based on an implicit assumption about a default, or fixed, mode of working memory storage. In contrast, here we asked whether the anticipated task might determine the format in which information is maintained in working memory, consistent with its task-oriented function. To test this flexible maintenance hypothesis, we recorded EEG while subjects performed a delayed (Yes/No) recognition task with different requirements and loads. Across three experiments, we compared event-related potentials (ERPs) in conditions with and without the necessity of maintaining conjunctions between features, while controlling for differences in visual stimulation. In Experiment 1 (N=24), involving color-location conjunctions, we identified a delay-period effect characterized by a positive potential shift in central-parietal channels when conjunction was not required by the task. This pattern, distinct from the effect caused by an increased working memory load, was confirmed in Experiment 2 (N=23) with an independent group of subjects using a similar paradigm, while also controlling for the physical appearance of probes. Finally, the observation of color and location conjunction in Experiments 1 and 2 was extended to Color and Orientation conjunction in Experiment 3 (N=22). Collectively, these three experiments provided reliable evidence demonstrating that the maintenance of feature conjunctions in working memory, whether spatial (location) or non-spatial (non-location), depends on the task goal.

Capturing the emergent dynamical structure in biophysical neural models
Complex neural systems can display structured emergent dynamics. Capturing this structure remains a significant scientific challenge. Using information theory, we apply Dynamical Independence (DI) to uncover the emergent dynamical structure in a minimal 5-node biophysical neural model, shaped by the interplay of two key aspects of brain organisation: integration and segregation. In our study, functional integration within the biophysical neural model is modulated by a global coupling parameter, while functional segregation is influenced by adding dynamical noise, which counteracts global coupling. DI defines a dimensionally-reduced macroscopic variable (e.g., a coarse-graining) as emergent to the extent that it behaves as an independent dynamical process, distinct from the micro-level dynamics. We measure dynamical dependence (a departure from dynamical independence) for macroscopic variables across spatial scales. Our results indicate that the degree of emergence of macroscopic variables is relatively minimised at balanced points of integration and segregation and maximised at the extremes. Additionally, our method identifies to which degree the macroscopic dynamics are localised across microlevel nodes, thereby elucidating the emergent dynamical structure through the relationship between microscopic and macroscopic processes. We find that deviation from a balanced point between integration and segregation results in a less localised, more distributed emergent dynamical structure as identified by DI. This finding suggests that a balance of functional integration and segregation is associated with lower levels of emergence (higher dynamical dependence), which may be crucial for sustaining coherent, localised emergent macroscopic dynamical structures. This work also provides a complete computational implementation for the identification of emergent neural dynamics that could be applied both in silico and in vivo.

Endothelial cell Nrf2 controls neuroinflammation following a systemic insult
Systemic inflammation can lead to neuroinflammation with acute consequences such as delirium and long-lasting deleterious effects including cognitive decline and the exacerbation of neurodegenerative disease progression. Here we show that the activation status of the transcription factor Nrf2 in endothelial cells is a critical regulator of this process. We found that peripheral inflammation caused infiltration of macrophages, microglial activation and inflammatory reactive astrogliosis, all of which could be prevented by RTA-404, an activator of the transcription factor Nrf2 and close structural relative of the recently FDA-approved Nrf2 activator RTA-408 (Omaveloxolone). To identify the key cellular mediator(s), we generated an endothelial cell-specific Nrf2 knockout mouse. Strikingly, the effects of RTA-404 on brain endothelial activation and downstream neuroinflammatory events was abolished by endothelial cell-specific Nrf2 deletion. This places endothelial cell Nrf2 as a peripherally accessible therapeutic target to reduce the CNS-adverse consequences of systemic inflammation.

Opto2P-FCM: A MEMS based miniature two-photon microscope with two-photon patterned optogenetic stimulation
Multiphoton microscopy combined with optogenetic photostimulation is a powerful technique in neuroscience enabling precise control of cellular activity to determine the neural basis of behavior in a live animal. Two-photon patterned photostimulation has taken this further by allowing interrogation at the individual neuron level. However, it remains a challenge to implement imaging of neural activity with spatially patterned two-photon photostimulation in a freely moving animal. We developed a miniature microscope for high resolution two-photon fluorescence imaging with patterned two-photon optogenetic stimulation. The design incorporates a MEMS scanner for two-photon imaging and a second beam path for patterned two-photon excitation in a compact and lightweight design that can be head-attached to a freely moving animal. We demonstrate cell-specific optogenetics and high resolution MEMS based two-photon imaging in a freely moving mouse. The new capabilities of this miniature microscope design can enable cell-specific studies of behavior that can only be done in freely moving animals.

Hearing thresholds in the bat Carollia perspicillata vary by sex but not age
Bats rely heavily on auditory perception for critical behaviors including navigation (echolocation) and conspecific communication. However, there is little information on the impacts of age and sex on the bat auditory system. Here, we used auditory brainstem response recordings to measure auditory thresholds in Carollia perspicillata (Seba's short-tailed bat). We did not detect an age-related threshold shift at the age range examined (1-8 years old), suggesting that bats may be relatively resistant to age-related hearing loss. We had considerably more young bats (aged 1-2 years) than older animals (aged 4-8 years), so our results should be interpreted with caution. However, they are consistent with other studies showing that bats exhibit fewer signs of aging relative to other small mammals. In addition, we show significantly lower auditory thresholds among females compared to age-matched males, similar to sex differences reported in other mammals. Finally, we found increased thresholds in a single non-pigmented bat relative to age- and sex-matched conspecifics. While preliminary, this finding suggests that pigmentation may be important for inner ear function in bats, similar to results from other mammals.

The spatio-temporal dynamics of phoneme encoding in aging and aphasia
During successful language comprehension, speech sounds (phonemes) are encoded within a series of neural patterns that evolve over time. Here we tested whether these neural dynamics of speech encoding are altered for individuals with a language disorder. We recorded EEG responses from individuals with post-stroke aphasia and healthy age-matched controls (i.e., older adults) during 25 min of natural story listening. We estimated the duration of phonetic feature encoding, speed of evolution across neural populations, and the spatial location of encoding over EEG sensors. First, we establish that phonetic features are robustly encoded in EEG responses of healthy older adults. Second, when comparing individuals with aphasia to healthy controls, we find significantly decreased phonetic encoding in the aphasic group after shared initial processing pattern (0.08-0.25s after phoneme onset). Phonetic features were less strongly encoded over left-lateralized electrodes in the aphasia group compared to controls, with no difference in speed of neural pattern evolution. Finally, we observed that phonemes with high uncertainty about word identity were encoded longer in controls than in individuals with aphasia. This indicates that encoding phonetic information until word identity is resolved might be a crucial mechanism for successful speech comprehension. Together, our results suggest that aphasia may entail failure to maintain lower-order information long enough to recognize lexical items.

Impairment of Neuronal Activity in the Dorsolateral Prefrontal Cortex Occurs Early in Parkinsonism
Background: Parkinson's disease (PD) is often characterized by altered rates and patterns of neuronal activity in the sensorimotor regions of the basal ganglia thalamocortical network. Little is known, however, regarding how neuronal activity in the executive control network of the brain changes in the parkinsonian condition. Objective: Investigate the impact of parkinsonism on neuronal activity in the dorsolateral prefrontal cortex (DLPFC), a key region in executive control, during a go/nogo reaching task. Methods: Using a within-subject design, single and multi-unit neuronal activity was recorded in the DLPFC of a nonhuman primate before and after the induction of mild parkinsonism using the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Results: Coincident with development of mild parkinsonian motor signs, there was a marked reduction in the percentage of DLPFC cells with significant task-related firing rate modulation during go and nogo conditions. Conclusions: These results suggest that DLPFC dysfunction may occur early in parkinsonism and contribute to cognitive impairments and disrupted executive function often observed in PD patients.

Astrocyte TrkB.T1 deficiency disrupts glutamatergic synaptogenesis and astrocyte-synapse interactions.
Perisynaptic astrocyte processes (PAPs) contact pre- and post-synaptic elements to provide structural and functional support to synapses. Accumulating research demonstrates that the cradling of synapses by PAPs is critical for synapse formation, stabilization, and plasticity. The specific signaling pathways that govern these astrocyte-synapse interactions, however, remain to be elucidated. Herein, we demonstrate a role for the astrocyte TrkB.T1 receptor, a truncated isoform of the canonical receptor for brain derived neurotrophic factor (BDNF), in modulating astrocyte-synapse interactions and excitatory synapse development. Neuron-astrocyte co-culture studies revealed that loss of astrocyte TrkB.T1 disrupts the formation of PAPs. To elucidate the role of TrkB.T1 in synapse development, we conditionally deleted TrkB.T1 in astrocytes in mice. Synaptosome preparations were employed to probe for TrkB.T1 localization at the PAP, and confocal three-dimensional microscopy revealed a significant reduction in synapse density and astrocyte-synapse interactions across development in the absence of astrocytic TrkB.T1. These findings suggest that BDNF/TrkB.T1 signaling in astrocytes is critical for normal excitatory synapse formation in the cortex and that astrocyte TrkB.T1 serves a requisite role in astrocyte synapse interactions. Overall, this work provides new insights into the molecular mechanisms of astrocyte-mediated synaptogenesis and may have implications for understanding neurodevelopmental disorders and developing potential therapeutic targets.

Executive control can query hidden human memories
When we try to retrieve a representation from visual long-term memory there is a chance that we will fail to recall seeing it even though the memory is stored in our brain. Here we show that although mechanisms of explicit memory retrieval are sometimes unable to retrieve stored memories, that mechanisms of executive control can quickly query memory and determine if a representation is stored therein. Our findings suggest that the representations stored in human memory that cannot be accessed explicitly at that moment are nonetheless directly accessible by the brain's higher level control mechanisms.

Transcutaneous Vagus Nerve Stimulation Boosts Post-Error Accuracy During Perceptual Decision-Making
The locus coeruleus-norepinephrine (LC-NE) system is a well-established regulator of behavior, yet its precise role remains unclear. Animal studies predominantly support a ''gai'' hypothesis, suggesting that the LC-NE system enhances sensory processing, while human studies have proposed an alternative ''urgenc'' hypothesis, postulating that LC-NE primarily accelerates responses. To address this discrepancy, we administered transcutaneous vagus nerve stimulation (tVNS) in two experiments involving 43 participants. In the first experiment, we showed that 4-second tVNS trains reliably induced greater pupil dilation compared to SHAM condition, indicating increased LC-NE activity. In the second experiment, we applied tVNS during a random dot motion task to assess its impact on perceptual decision-making. Notably, tVNS improved accuracy without affecting reaction times, which appears inconsistent with the ''urgenc'' hypothesis. Drift-diffusion model analyses further supported the ''gai'' hypothesis, revealing that tVNS increased the drift rate, indicative of enhanced evidence accumulation. Accuracy and drift-rate improvements were especially pronounced following errors and in less proficient participants, who otherwise exhibited post-error declines in these measures under SHAM condition. Our findings suggest that the influence of the LC-NE system adapts to task demands, becoming especially beneficial in challenging contexts. Overall, this study underscores the potential of tVNS as a non-invasive tool to investigate the causal role of the LC-NE system in human behavior.

Cell type-specific driver lines targeting the Drosophila central complex and their use to investigate neuropeptide expression and sleep regulation
The central complex (CX) plays a key role in many higher-order functions of the insect brain including navigation and activity regulation. Genetic tools for manipulating individual cell types, and knowledge of what neurotransmitters and neuromodulators they express, will be required to gain mechanistic understanding of how these functions are implemented. We generated and characterized split-GAL4 driver lines that express in individual or small subsets of about half of CX cell types. We surveyed neuropeptide and neuropeptide receptor expression in the central brain using fluorescent in situ hybridization. About half of the neuropeptides we examined were expressed in only a few cells, while the rest were expressed in dozens to hundreds of cells. Neuropeptide receptors were expressed more broadly and at lower levels. Using our GAL4 drivers to mark individual cell types, we found that 51 of the 85 CX cell types we examined expressed at least one neuropeptide and 21 expressed multiple neuropeptides. Surprisingly, all co-expressed a small neurotransmitter. Finally, we used our driver lines to identify CX cell types whose activation affects sleep, and identified other central brain cell types that link the circadian clock to the CX. The well-characterized genetic tools and information on neuropeptide and neurotransmitter expression we provide should enhance studies of the CX.

Revealing Acute Consequences of Rapid Protein Elimination at Individual Synapses using Auxin-Inducible Degron 2 Technology
A powerful approach to assess a protein of interest (POI) function is its specific elimination. Common knock-out and knock-down strategies, however, are protracted and often irreversible, challenging the assessment of acute or temporary consequences in the same cells and tissues. Here we describe the use of Auxin-Inducible Degron 2 (AID2) technology to study the real-time consequences of acute POI elimination in nerve cell synapses. We demonstrate its capacity in cultured neurons and in vivo to rapidly eliminate postsynaptic scaffold proteins fused at N-terminal, C-terminal, or nested sites to GFP derivatives or HaloTag. We show that acute PSD-95 or gephyrin elimination leads to the concomitant loss of AMPA or GABAA receptors at the same synapses, and that, surprisingly, acute GKAP, but not PSD-95 elimination reduces postsynaptic scaffold size. Our findings highlight the utility of AID2 technology for rapidly eliminating synaptic POIs and studying real-time consequences in the same neurons and synapses.

Transcriptomic profiling of unmethylated full mutation carriers implicates TET3 in FMR1 CGG repeat expansion methylation dynamics in Fragile X syndrome
Background Fragile X syndrome (FXS) is a neurodevelopmental disorder caused by the expansion of a CGG repeat in the 5'UTR of the FMR1 (fragile X messenger ribonucleoprotein 1) gene. Healthy individuals possess a repeat 30-55 CGG units in length. Once the CGG repeat exceeds 200 copies it triggers methylation at the locus. This methylation covers the FMR1 promoter region and silences expression of the gene and the production of FMRP (fragile X messenger ribonucleoprotein). The loss of FMRP is responsible for a number of pathologies including neurodevelopmental delay and autism spectrum disorder. Methylation of the expanded repeat in the FMR1 locus is the causal factor for FXS, however it is not known why the expanded repeat triggers this epigenetic change or how exactly DNA methylation is established. Intriguingly, genetic engineering of expanded CGG repeats of over 300x in the FMR1 locus in mice remains unmethylated. Also in humans, in very rare cases, individuals can have an FMR1 CGG expansion >200x but the locus remains unmethylated. These unmethylated full mutation individuals give us a rare opportunity to investigate the mechanism of FMR1 promoter methylation. Methods Fibroblasts were obtained from a healthy control, an FXS patient and two unmethylated full expansion carriers. RNA was extracted and comparative transcriptomic analysis was performed on all samples. Whole genome sequencing was carried out on DNA from the two UFM carriers and the results analysed to investigate DNA variants that could explain the observed differences in gene expression. Results Our analyses focused on genes involved in epigenetic modification. We show that Tet methylcytosine dioxygenase 3 (TET3), a gene involved in DNA methylation, is significantly downregulated in UFM carriers compared to healthy controls or FXS patient derived cells. Genomic analyses reveal a number of rare variants present in the TET3 locus in UFM carriers when compared to the reference genome. No single variant has a significant predicted effect, raising the possibility that a trans acting variant could be driving the differential gene expression. Conclusion Our results suggest that TET3 is a candidate factor responsible for the lack of methylation of the expanded FMR1 locus. Further analyses are needed to further elucidate this relationship, however given its potential to directly interact with CGG repeats and its ambiguous role in 5-hydroxy-methylation of CG containing sequences, TET3 is a strong candidate for further exploration.

Enhanced human sensorimotor integration via self-modulation of the somatosensory activity
Kinesthetic motor imagery, the mental rehearsal of movement and its associated sensations activates somatosensory and motor cortices. Motor imagery improves performance in neurorehabilitation, sports, and instrument play. However, the mechanism that enhances performance through repetitive motor imagery remains unclear. Here, we combined individually tailored motor imagery training combined with closed-loop neurofeedback training, neurophysiology, and behavioral assessment to characterize how the training can modulate the somatosensory system and improve performance. The closed-loop training using real-time feedback of human electroencephalogram (EEG) signals enhanced participants' self-modulation ability of intrinsic neural oscillations in the primary somatosensory cortex (S1) within 30 minutes. Further, the short-term reorganization in S1 was corroborated by the post-training reactivity enhancement revealed by changes in somatosensory evoked potential (SEP) amplitude of early component originating from S1. Meanwhile those derived from peripheral sensory fibers were maintained, suggesting that the closed-loop training manipulated cortical activities. Behavioral evaluation demonstrated improved performance during keyboard touch-typing indexed by resolved the speed-accuracy trade-off. Collectively, our results provide evidence that mentally rehearsed movement during kinesthetic motor imagery induces functional reorganization of S1 activities that can contribute to performance improvement.

Viral vectors with cluster of differentiation gene promoters to target specific cell types in the brain
Understanding brain function and developing targeted therapies for neurological disorders require precise access to specific cell types, but current methods are limited. Here, we report the development of cell-type specific adeno-associated virus (AAV) vectors utilizing promoters of cluster of differentiation genes (CD promoters) for targeted gene delivery in the brain. We newly identified CD promoters that induce gene expression selectively in specific cell types in the mouse brain. These AAVs enable in vivo calcium imaging and chemogenetic applications in specific cerebellar cells, revealing distinct and shared roles of two types of cerebellar interneurons. Notably, chemogenetic modulation of cerebellar molecular layer interneurons using a CD promoter rescued social behavior and motor deficits in a mouse model of autism spectrum disorder. Our findings demonstrate the utility of these AAVs in elucidating the functions of individual cell types in brain function and in developing novel, cell-type specific therapies for brain diseases.

Spatial memory in Alzheimer's disease 5XFAD mice is enhanced by XPO1 inhibitor KPT-330
The proteostatic decline in Alzheimer's disease is well established and improvement in proteostasis could potentially delay cognitive impairment. One emerging entry point to modulate proteostasis is the regulation of nucleo-cytoplasmic partitioning of proteins across the nuclear pore via karyopherins. The nuclear exportin XPO1 is a key regulator of proteostasis by driving the assembly of ribosomes and by modulating the process of autophagy. We recently found that XPO1 inhibitor KPT-330 (Selinexor), an FDA approved drug against multiple myelomas, enhances proteostasis, leading to benefits in models of neurodegenerative diseases in C. elegans and Drosophila. Here, we find that KPT-330 increases autophagy in murine neuronal cells and improves spatial memory performance in a murine model of Alzheimer's disease (5XFAD). Unexpectedly, general amyloid deposition in several brain regions was significantly increased by KPT-330, but specific regions, especially the thalamus, displayed significantly lower deposition, suggesting that XPO1 inhibition has regional-specific effects on proteostasis and amyloid plaque formation. Altogether, we conclude that XPO1 inhibition can improve cognition via spatially specific reductions in amyloid deposition.

Visual objects refine head direction coding
Animals use visual objects to guide navigation-related behaviors, from hunting prey, to escaping predators, to exploring the world. However, little is known about where visual objects are encoded in the mouse brain or how visual objects impact processing within the spatial navigation system. Using functional ultrasound (fUS) imaging in mice, we conducted a brain-wide screen and identified brain areas that were preferentially activated by images of objects compared to scrambled versions of the same stimuli. While visual cortical areas did not show a significant preference, regions associated with spatial navigation were preferentially activated by visual objects. Electrophysiological recordings in the postsubiculum, the primary cortical area of the head direction (HD) system, further confirmed a preference for visual objects, which was present in both HD cells and fast-spiking interneurons. Finally, we found that visual objects dynamically modulate HD cells, selectively increasing firing rates for HD cells aligned with a visual landmark's direction, while suppressing activity in HD cells coding for other directions. These results reveal that visual objects refine population-level coding of head direction.

Vicarious Somatotopic Maps Tile Visual Cortex
Our sensory systems work together to generate a cohesive experience of the world around us. Watching others being touched activates brain areas representing our own sense of touch: the visual system recruits touch-related computations to simulate bodily consequences of visual inputs. One long-standing question is how the brain implements this interface between visual and somatosensory representations. To address this question, we developed a method to simultaneously map somatosensory body part tuning and visual field tuning throughout the brain. Applying this method on ongoing co-activations during rest resulted in detailed maps of the body-part tuning in the brain's endogenous somatotopic network. During movie watching, somatotopic tuning explains responses throughout the entire dorsolateral visual system, revealing an array of somatotopic body maps that tile the cortical surface. The tuning of these maps aligned with those of visual maps, and predicted both preferences for visual field locations and the visual-category preferences for body parts. These results reveal a mode of brain organization in which aligned visual-somatosensory topographic maps connect visual and bodily reference frames. This cross-modal interface is ideally situated to translate raw sensory impressions into more abstract formats useful for action, social cognition, and semantic processing.

The forgotten psychedelic: Spatiotemporal mapping of brain organisation following the administration of 2C-B and psilocybin
As psychedelic-assisted psychotherapy gains momentum, clinical investigation of next-generation psychedelics may lead to novel compounds tailored for specific populations. 2,5-dimethoxy-4-bromophenethylamine (2C-B) is a psychedelic phenethylamine reported to produce less dysphoria and subjective impairment than the psychedelic tryptamine psilocybin. Despite its popularity among recreational users and distinct pharmacodynamics, the neural correlates of 2C-B remain unexplored. Using 7T resting-state functional MRI in 22 healthy volunteers, we mapped out the acute effects of matched doses of 20 mg 2C-B, 15 mg psilocybin and placebo across spatiotemporal benchmarks of functional brain organisation. In a within-subjects, double-blind, placebo-controlled crossover design, we evaluated the neuropharmacological and neurobehavioural correlates of an array of connectivity measures - including static (sFC) and global connectivity (gFC), dynamic connectivity variability (dFC), and spontaneous brain complexity. Compared to placebo, 2C-B and psilocybin selectively reduced intra-network sFC, while broadly increasing between-network and subcortical-cortical connectivity. Compared to psilocybin, 2C-B exhibited less pronounced reductions in between-network FC but elicited elevations in transmodal sFC. Both compounds yielded spatially divergent increases in gFC yet produced similar increases in brain complexity. Using PET density modelling, the spatial distribution of neural effects aligned with documented differences in monoaminergic transporter and serotonergic receptor binding affinity beyond 5-HT2A, highlighting the role of pharmacology in shaping functional dynamics. Lastly, we show behavioural markers of psychedelic effects are non-linearly reflected by the desynchronisation of the transmodal axis of functional brain organisation. Together, our findings highlight 2C-B as a useful new addition to the study of psychedelic neuroscience and may motivate new pharmacotherapy strategies.

Functional Ultrasound Imaging Reveals Activation Properties of Clinical Spinal Cord Stimulation
Objectives: Spinal cord stimulation (SCS) therapy has long been established as an effective treatment for chronic neuropathic pain. However, methodological limitations have prohibited the detailed investigation of the activation patterns produced in the spinal cord during therapy. Functional ultrasound (fUS) is an emerging technology that monitors local hemodynamic changes in the brain that are tightly coupled to neural functional activity [1-3]. Previous studies have demonstrated that the high sensitivity and spatiotemporal resolution of fUS can be used to monitor activation in the spinal cord [4, 5]. In this study, fUS was used to investigate neuromodulation patterns produced by clinical SCS paradigms in an ovine model that enabled testing with implanted clinical hardware. Materials and Methods: Activation of local dorsal horn regions during SCS therapy was evaluated using fUS to detect hemodynamic changes in flowing spinal blood volume ({triangleup}SBV). Briefly, male ovine subjects were anesthetized and laminectomies were performed at T12-L1 to expose the spinal cord. The spine was mechanically fixed to reduce breathing-induced motion. Standard SCS leads were percutaneously implanted midline overlying the dura of the exposed cord to enable stimulation and recording. A second lead was implanted in the epidural space anterior to the laminectomy for recording evoked compound action potentials (eCAPs). Motor thresholds were determined from electromyographic (EMG) signals recorded from subdermal needle electrodes. Hemodynamic activation patterns produced by SCS therapy were mapped across two vertebral segments in the superficial dorsal horn (SDH) at amplitudes between 100%-200% eCAP threshold (eCAPT). The magnitude and volume of significant {triangleup}SBV during SCS was quantified and compared across conditions. Results: eCAP and motor thresholds varied widely between different representative SCS programs in current clinical use. Compared with motor threshold, we found eCAPT to be a more stable and reliable ratiometric reference to establish neural drive from stimulation, consistent with previous literature [6]. SCS stimulation resulted in significant activation of the SDH in differing patterns across two vertebral segments. The magnitude and volume of {triangleup}SBV increased at higher amplitudes and was typically maximal in the SDH regions underlying the active electrodes. Activation persisted for several seconds following SCS therapy cessation, suggesting the engagement of neurophysiological processes with correspondingly long time constants. In addition, therapy mode significantly influenced total area and depth of {triangleup}SBV. Multiphase therapy produced a larger area of {triangleup}SBV that extended deeper into the spinal cord relative to single phase therapies. Conclusions: This work demonstrates that fUS can effectively measure SCS neural response patterns in the pain processing laminae of a large animal model implanted with a clinical SCS system. Hemodynamic responses in the spinal cord varied significantly across SCS therapy modes, with Multiphase stimulation providing a greater area of coverage and depth of response versus other common stimulation types.

Functional and causal neural mechanisms of human voice perception in noisy situations
Human communication entails an efficient way of simultaneously processing voice and reducing the impact of environmental noise. By manipulating background noise, we aimed at clarifying the neural mechanisms allowing voice comprehension in noisy situations. Our results point to spatial and temporal coexistence of lateral and medial temporal cortex networks when voice is easily detected in highly noisy conditions, revealing the necessary neural underpinnings of human communication in realistic situations.

Connectome-based Predictive Models of General and Specific Cognitive Control
Cognitive control, the ability to adapt thoughts and actions to shifting contexts and goals, is composed primarily of three distinct yet interrelated components: Inhibition, Shifting, and Updating. While prior research has examined the nature of different cognitive components as well as their inter-relationships, fewer studies examined whole-brain connectivity to predict individual differences for the three cognitive components and associated tasks. Here, using the Connectome-based Predictive Modelling (CPM) approach and open-access data from the Human Connectome Project, we built brain network models to successfully predict individual performance differences on the Flanker task, the Dimensional Change Card Sort task, and the 2-Back task, each putatively corresponding to Inhibition, Shifting, and Updating. We focused on grayordinate fMRI data collected during the 2-Back tasks after confirming superior predictive performance over resting-state and volumetric data. High cross-task prediction accuracy as well as joint recruitment of canonical networks, such as the frontoparietal and default-mode networks, suggest the existence of a common cognitive control factor. To directly investigate the relationships among the three cognitive control components, we developed new measures to disentangle their shared and unique aspects. Our analysis confirmed that a shared control component can be well predicted from functional connectivity patterns densely located around the frontoparietal, default-mode and dorsal attention networks. In contrast, the Shifting-specific and Inhibition-specific components exhibited lower cross-prediction performance, indicating their distinct and specialized roles. Notably, the Updating-specific component showed significant cross-prediction with the general control factor, suggesting its central role in cognitive control. Given the limitation that individual behavioral measures do not purely reflect the intended cognitive constructs, our study demonstrates the need to distinguish between common and specific components of cognitive control.

Human short association fibers are thinner and less myelinated than long fibers
The size and complexity of the human brain requires optimally sized and myelinated fibers. White matter fibers facilitate fast communication between distant areas, but also connect adjacent cortical regions via short association fibers. The fundamental questions of i) how thick these fibers are and ii) how strongly they are myelinated, however, remain unanswered. We present a comprehensive analysis of ~400,000 fibers of human white matter regions with long (corpus callosum) and short fibers (superficial white matter). We demonstrate a substantially smaller fiber diameter and lower myelination in superficial white matter than in the corpus callosum. Surprisingly, we do not find a difference in the ratio between axon diameter and myelin thickness (g-ratio), which is close to the theoretically optimal value of ~0.6 in both areas. For the first time, to our knowledge, we shed light on a fundamental principle of brain organization that will be essential to understand the human brain.

Parkinsonism disrupts neuronal modulation in the pre-supplementary motor area during movement preparation
Multiple studies suggest that Parkinson's disease (PD) is associated with changes in neuronal activity throughout the basal ganglia-thalamocortical motor circuit. There are limited electrophysiological data, however, describing how parkinsonism impacts neuronal activity in the pre-supplementary motor area (pre-SMA), an area in medial frontal cortex involved in movement planning and motor control. In this study, single unit activity was recorded in the pre-SMA of two non-human primates during a visually cued reaching task in both the naive and parkinsonian state using the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of parkinsonism. In the naive state neuronal discharge rates were dynamically modulated prior to the presentation of the instructional go-cue. In a subset of these modulated cells, the magnitude of modulation correlated linearly with reaction time (RT). In the parkinsonian state, however, modulation of discharge rates in the pre-SMA was disrupted and the predictive encoding of RT was significantly diminished. These findings add to our understanding of the role of pre-SMA in motor behavior and suggest that disrupted encoding in this cortical area contributes to the alteration of early preparatory and pre-movement processes that are present in Parkinson's disease.

An end-to-end model of active electrosensation
Weakly electric fish localize and identify objects by sensing distortions in a self-generated electric field. Fish can determine the resistance and capacitance of an object, for example, even though the field distortions being sensed are small and highly-dependent on object distance and size. Here we construct a model of the responses of the fish's electroreceptors on the basis of experimental data, and we develop a model of the electric fields generated by the fish and the distortions due to objects of different resistances and capacitances. This provides us with an accurate and efficient method for generating large artificial data sets simulating fish interacting with a wide variety of objects. Using these sets, we train an artificial neural network (ANN), representing brain areas downstream of electroreceptors, to extract the 3D location, size, and electrical properties of objects. The model performs best if the ANN operates in two stages: first estimating object distance and size and then using this information to extract electrical properties. This suggests a specific form of modularity in the electrosensory system that can be tested experimentally and highlights the potential of end-to-end modeling for studies of sensory processing.

Arc mediates intercellular tau transmission via extracellular vesicles
Intracellular neurofibrillary tangles that consist of misfolded tau protein1 cause neurodegeneration in Alzheimer's disease (AD) and frontotemporal dementia (FTD). Tau pathology spreads cell-to-cell2 but the exact mechanisms of tau release and intercellular transmission remain poorly defined. Tau is released from neurons as free protein or in extracellular vesicles (EVs)3-5 but the role of these different release mechanisms in intercellular tau transmission is unclear. Here, we show that the neuronal gene Arc is critical for packaging tau into EVs. Brain EVs purified from human tau (hTau) transgenic rTg4510 mice (rTgWT) contain high levels of hTau that are capable of seeding tau pathology. In contrast, EVs purified from rTgWT crossed with Arc knock-out mice (rTgArc KO) have significantly less hTau and cannot seed tau aggregation. Arc facilitates the release of hTau in EVs produced via the I-BAR protein IRSp53, but not free tau. Arc protein directly binds hTau to form a fuzzy complex that we identified in both mouse and human brain tissue. We find that pathological intracellular hTau accumulates in neurons in rTgArc KO mice, which correlates with accelerated neuron loss in the hippocampus. Finally, we find that intercellular tau transmission is significantly abrogated in Arc KO mice. We conclude that Arc-dependent release of tau in EVs plays a significant role in intracellular tau elimination and intercellular tau transmission.

Bcl11b orchestrates subcerebral projection neuron axon development via cell-autonomous, non-cell-autonomous, and subcellular mechanisms
Both cell-intrinsic competency and extracellular cues regulate axon projection, but mechanisms that coordinate these elements remain poorly understood. Subcerebral projection neurons (SCPN) extend their primary axons from cortex through subcortical structures, including the striatum, targeting the brainstem and spinal cord. We identify that the transcription factor Bcl11b/Ctip2 functions in multiple independent neuron populations to control SCPN axon development. Bcl11b expressed by SCPN is required cell-autonomously for axonal outgrowth and efficient entry into the internal capsule within the striatum, while Bcl11b expressed by medium spiny neurons (MSN) non-cell-autonomously regulates SCPN axon fasciculation within the internal capsule and subsequent pathfinding. Further, integrated investigation of Bcl11b-null SCPN with transcriptomic, immunocytochemical, and in vivo growth cone purification approaches identifies that Cdh13 is localized along axons and on growth cone surfaces of SCPN in vivo, and mediates Bcl11b regulation of SCPN axonal outgrowth. Together, these results demonstrate that Bcl11b controls multiple aspects of SCPN axon development by coordinating intrinsic SCPN cell autonomous subcellular mechanisms and extrinsic MSN non-cell-autonomous mechanisms.

Hierarchical emergence of opponent coding in auditory belt cortex
We recorded from neurons in primary auditory cortex (A1) and middle-lateral belt area (ML) while rhesus macaques either discriminated amplitude-modulated noise (AM) from unmodulated noise or passively heard the same stimuli. We used several post-hoc pooling models to investigate the ability of auditory cortex to leverage population coding for AM detection. We find that pooled-response AM detection is better in the active condition than the passive condition, and better using rate-based coding than synchrony-based coding. Neurons can be segregated into two classes based on whether they increase (INC) or decrease (DEC) their firing rate in response to increasing modulation depth. In these samples, A1 had relatively fewer DEC neurons (26%) than ML (45%). When responses were pooled without segregating these classes, AM detection using rate-based coding was much better in A1 than in ML, but when pooling only INC neurons, AM detection in ML approached that found in A1. Pooling only DEC neurons resulted in impaired AM detection in both areas. To investigate the role of DEC neurons, we devised two pooling methods that opposed DEC and INC neurons - a direct subtractive method and a two-pool push-pull opponent method. Only the push-pull opponent method resulted in superior AM detection relative to indiscriminate pooling. In the active condition, the opponent method was superior to pooling only INC neurons during the late portion of the response in ML. These results suggest that the increasing prevalence of the DEC response type in ML can be leveraged by appropriate methods to improve AM detection.

Cannabidiol reverses microglia activation and loss of parvalbumin interneurons and perineuronal nets in a mouse model of schizophrenia
Cannabidiol (CBD) has shown potential for treating schizophrenia (SCZ) by targeting its positive, negative, and cognitive symptoms. In this study, we investigated if CBD could reverse the memory impairment observed after chronic administration of the NMDA receptor antagonist. MK-801 treatment (0.5 mg/kg i.p., twice a day, for 14 days) resulted in short- and long-term memory deficits and decreased relative power of {gamma} oscillation in freely moving animals. CBD administration (60 mg/kg i.p. daily for seven days after the MK-801 treatment period) reversed these changes. The positive cognitive effects of CBD were prevented by a 5-HT1A, but not a CB2, receptor antagonist. On the cellular level, CBD reversed MK-801-induced reduced number of parvalbumin-positive neurons and their associated perineuronal nets in the prelimbic medial prefrontal cortex (mPFC) and ventral hippocampus (vHip). This neuroprotective effect was mediated by 5-HT1A and CB2 receptors in the vHip but was independent of these receptors in the mPFC. Additionally, CBD reversed MK-801-induced microglial activation in both mPFC and vHip, again through 5-HT1A and CB2 receptors. These findings suggest that CBD modulates multiple pathways affected in SCZ-like conditions, offering a promising therapeutic avenue for SCZ treatment.

Oxytocin neurons signal state-dependent transitions to thermogenesis and behavioral arousal in social and non-social settings.
Mammalian thermoregulatory behaviors such as thermal comfort seeking, physical activity, nesting, and huddling operate alongside autonomic responses such as brown fat thermogenesis and peripheral vasodilation to defend core body temperature (Tb) 1-4. The defended Tb is not held constant, but alternates across active/rest and behavioral cycles 5-9. Although the thermoregulatory behaviors facilitating these alternations are controlled by the brain, the underlying neural populations are poorly understood. The oxytocin system has been proposed to contribute to behavioral thermoregulation 10,11, yet evidence for how activity within oxytocin neurons relates to such pathways is lacking. Here, we identify neuronal dynamics underlying behavioral thermoregulation in mice. We show that the paraventricular hypothalamus (PVN) and PVN oxytocin (PVNOT) neurons are selectively activated during two thermoregulatory states: active and quiescent huddling. Next, activation and inhibition of PVNOT neurons reveals effects on Tb, peripheral vasodilation, and warm seeking, establishing a role in thermoeffector pathways. We then demonstrate that in vivo PVNOT calcium activity tracks the patterning of thermoregulatory behaviors. Across social contexts, PVNOT peaks occur during low Tb (~36.0{degrees}C) and during transitions towards physical activity and thermogenesis. In the solo context, PVNOT peaks predict the offset of quiescence and onset of post-quiescence nesting. In the paired context, PVNOT peaks predict the offset of quiescent huddling and onset of post-quiescent active huddling. Our study provides evidence for a role of PVNOT neurons during the offset of rest and the onset of behavioral arousal and thermogenesis and provides a foundation for understanding the coordination between thermal homeostasis and animal behavior.

Relationship as resource or burden? Associations of attachment style, relationship quality and dyadic coping with acute psychosocial stress in the presence of the romantic partner
Stress is a wide-spread phenomenon and associated with various detrimental health effects. A significant resource for stress buffering is social support. How social support is perceived, however, depends on a multitude of individual and interindividual factors. This study aimed to explore the stress-reducing properties of relationship-inherent variables. We investigated the association of attachment style, relationship quality and dyadic coping, with subjective and physiological stress responses to a psychosocial laboratory stressor in romantic partners. Seventy-nine couples participated, with one partner ("target") undergoing the Trier Social Stress Test and the other ("observer") observing the situation. Besides examining the role of targets' relationship variables, we also assessed the link between observers' relationship variables and targets' stress reactivity. We found that both targets' and observers' insecure-avoidant attachment scores were associated with targets' stress reactivity. In detail, while targets' insecure-avoidant attachment scores were negatively associated with targets' subjective stress experience, observers' insecure-avoidant attachment scores were positively associated with targets' heart rate reactivity. Further, higher insecure-avoidant attachment scores linked to lower psycho-endocrine covariance, i.e., a lower accordance between self-reported and cortisol stress responding. On the one hand, these data may suggest that under stress, insecure-avoidantly attached individuals suppress their experience of stress to preserve a sense of independence as part of their deactivating attachment strategy. The presence of an insecure-avoidantly attached partner during a stressful experience, on the other hand, seems to be a stressor rather than a source of support. Long-term, an insecure-avoidantly attached partner may negatively impact an individual's stress-related health and wellbeing.

Network analysis of α-synuclein pathology progression reveals p21-activated kinases as regulators of vulnerability
-Synuclein misfolding and progressive accumulation drives a pathogenic process in Parkinson's disease. To understand cellular and network vulnerability to -synuclein pathology, we developed a framework to quantify network-level vulnerability and identify new therapeutic targets at the cellular level. Full brain -synuclein pathology was mapped in mice over 9 months. Empirical pathology data was compared to theoretical pathology estimates from a diffusion model of pathology progression along anatomical connections. Unexplained variance in the model enabled us to derive regional vulnerability that we compared to regional gene expression. We identified gene expression patterns that relate to regional vulnerability, including 12 kinases that were enriched in vulnerable regions. Among these, an inhibitor of group II PAKs demonstrated protection from neuron death and -synuclein pathology, even after delayed compound treatment. This study provides a framework for the derivation of cellular vulnerability from network-based studies and identifies a promising therapeutic pathway for Parkinson's disease.

A 128-channel receive array with enhanced SNR performance for 10.5 tesla brain imaging
Purpose: To develop and characterize the performance of a 128-channel head array for brain imaging at 10.5 tesla and evaluate the potential of brain imaging at this unique, >10 tesla magnetic field. Methods: The coil is composed of a 16-channel self-decoupled loop transmit/receive array with a 112-loop receive-only (Rx) insert. Interactions between the outer transmitter and the inner 112Rx insert were mitigated using coaxial cable traps placed every 1/16 of a wavelength on each feed cable, locating most preamplifier boards outside the transmitter field and miniaturizing those placed directly on individual coils. Results: The 128-channel array described herein achieved 77% of ultimate intrinsic SNR in the center of the brain. Transmit field maps obtained experimentally on a phantom with and without the receive array were similar and matched EM simulations, leading to FDA approval for human imaging. Anatomical and functional data, including with power demanding sequences, were acquired successfully on human volunteers. Conclusions: Counterintuitive to expectations based on magnetic fields [≤]7T, the higher channel counts provided SNR gains centrally, capturing ~80% uiSNR. Fraction of uiSNR achieved centrally in 64Rx, 80Rx, and 128Rx arrays suggested that a plateau was being reached at 80%. At this plateau, linear to approximately quadratic B0 dependent SNR gains for the periphery and the center, respectively, were observed for 10.5T relative 7T.

40 Hz light stimulation restores early brain dynamics alterations and associative memory in Alzheimer's disease model mice
Visual gamma entrainment using sensory stimuli (vGENUS) is a promising non-invasive therapeutic approach for Alzheimer's disease (AD), showing efficacy in improving memory function. However, its mechanisms of action remain poorly understood. Using young AppNL-F/MAPT double knock-in (dKI) mice, a model of early AD, we examined brain dynamics alterations before amyloid plaque onset. High-density EEG recordings and novel metrics from fields outside neuroscience were used to assess brain dynamics fluidity - a measure of the brain's ability to transition between activity states. We revealed that dKI mice exhibit early, awake state-specific reductions in brain dynamics fluidity associated with cognitive deficits in complex memory tasks. Daily vGENUS sessions over two weeks restored brain dynamics fluidity and rescued memory deficits in dKI mice. Importantly, these effects built up during the stimulation protocol and persisted after stimulation ended, suggesting long-term modulation of brain function. Based on these results, we propose a "brain dynamics repair" mechanism for vGENUS that goes beyond current amyloid-centric hypotheses. This dual insight - that brain dynamics are both a target for repair and a potential diagnostic tool - provides new perspectives on early Alzheimer's disease pathophysiology.

The neural correlates of shared and individual experience
Contemporary neuroscience research typically focuses on shared contents of experience and common neural states. Conversely, we set out to explore the neural correlates of individual-specific experiences that shape the distinct traits of each person. We propose an approach through which we compute individual-specific dynamics of functional connectivity states. These dynamics do not require estimation of common states across individuals and can be directly related to dynamic behavioural ratings of subjective experience. To this end, we leverage a unique functional magnetic resonance imaging dataset where subjects listened to an engaging naturalistic story while awake and under different levels of anaesthesia, altering or abolishing conscious experience. We find that this method can detect correspondences between neural and subjective dynamics. We then show that the dynamics of the default mode network underlie more personal experiences of the story as they are more dissimilar between participants during awareness compared to unconsciousness. On the other hand, the auditory and posterior dorsal attention networks show higher inter-subject similarity in consciousness compared to unconsciousness and suggest that the dynamics of these networks support more generalisable experiences of the story. We further characterise individual-specific brain dynamics by showing that they are associated with higher complexity in consciousness, whilst conversely, brain dynamics underlying shared experience become less complex during the conscious experience of the story.

5-HT2C receptors in the nucleus accumbens constrain the rewarding effects of MDMA
MDMA is a promising adjunct to psychotherapy and has well-known abuse liability, although less than other amphetamine analogs. While the reinforcing dopamine (DA)-releasing properties of MDMA are on par with methamphetamine (METH), MDMA is a far more potent serotonin (5-HT) releaser, via the 5-HT transporter (SERT). MDMA-mediated 5-HT release in a major reward center, the nucleus accumbens (NAc), drives prosocial behaviors via 5-HT1BR activation. We hypothesized that this prosocial mechanism contributes to the reduced reinforcing properties of MDMA compared to METH and used a platform of assays to predict the balance of prosocial and abuse-linked effects of (R)-MDMA, a novel entactogen in clinical development. NAc DA release, measured by GRAB-DA photometry in vivo, increased in proportion to MDMA (7.5 and 15 mg/kg, i.p.) and METH (2 mg/kg i.p.)-conditioned place preference (CPP). Using conditional knockouts (cKOs) for DAT and SERT, microdialysis, and photometry, we found that MDMA-released 5-HT limited MDMA-released DA through actions in the NAc, rather than at ventral tegmental area DAergic cell bodies. SERT cKO reduced the MDMA dose required for CPP three-fold. This enhanced MDMA-CPP and increased DA release were replicated by intra-NAc infusion of either a 5-HT reuptake inhibitor (escitalopram) to prevent MDMA interaction with SERT, or a 5-HT2CR antagonist (SB242084), but not by the 5-HT1BR antagonist NAS-181. These data support separate mechanisms for the low abuse potential versus prosocial effect of MDMA. Using this platform of assays, (R)-MDMA is predicted to have prosocial effects and low abuse potential.

Proper reference selection and re-referencing to mitigate bias in single pulse electrical stimulation data
Single pulse electrical stimulation experiments produce pulse-evoked potentials used to infer brain connectivity. The choice of recording reference for intracranial electrodes remains non-standardized and can significantly impact data interpretation. When the reference electrode is affected by stimulation or evoked brain activity, it can contaminate the pulse-evoked potentials recorded at all other electrodes and influence interpretation of findings. We highlight this specific issue in intracranial EEG datasets from two subjects recorded at separate institutions. We present several intuitive metrics to detect the presence of reference contamination and offer practical guidance on different mitigation strategies. Either switching the reference electrode or re-referencing to an adjusted common average effectively mitigated the reference contamination issue, as evidenced by increased variability in pulse-evoked potentials across the brain. Overall, we demonstrate the importance of clear quality checks and preprocessing steps that should be performed before analysis of single pulse electrical stimulation data.

Space matters: virtual pedestrians with mobility constraints affect individuals' avoidance behaviours
Walking in urban settings requires people to negotiate crowds. In these situations, people typically want to maintain a level of personal space around themselves. Recent work on one-versus-one interactions demonstrated that whether one of the pedestrians looked distracted or interacted with an object (e.g., stroller, bike) predicted the medial-lateral separation between them as they walked past each other. However, this work did not distinguish between the type of object interaction (or mobility constraint) and thus, it is unclear whether different constraints have different effects on avoidance behaviours. Here we tested the hypothesis that the type of object an approaching pedestrian held or pushed would affect the extent of path deviation, which would also depend on whether that pedestrian was distracted. To address this hypothesis, we created an immersive virtual environment that consisted of a 3.5-m-wide paved urban path. Participants had to walk and avoid colliding with approaching virtual pedestrians that often held a shopping bag or pushed a bike or stroller while looking straight ahead or off to the side as if distracted. Distraction did not affect avoidance behaviours. However, participants increased medial-lateral separation with the virtual pedestrian at the time of crossing when a stroller was present compared to the other mobility constraints. The type of mobility constraint also differentially affected onset of deviation and rate of progression before and after a path deviation. These results support the idea that characteristics of the obstacle to avoid (in this case, a virtual pedestrian) influence collision avoidance behaviours.

Ketosis Elevates Antioxidants and Enhances Neural Function Through Improved Bioenergetics: A 1H MR Spectroscopy Study
Ketosis is known to alter the balance of neuroactive amino acids and enhance neural function when compared to a glycolytic condition. However, its influence on other metabolites, such as antioxidants and neural energy markers, and the mechanisms by which ketosis improves neural function remain unclear. Here, we measure the neurochemical effects of acute ketosis on the human brain using ultra-high-field 1H MR Spectroscopy (MRS) and investigate the subsequent impact on neural function through resting-state functional magnetic resonance imaging (rsfMRI). In a within-subjects design, N = 63 healthy adults from across the lifespan underwent 1H MRS and rsfMRI scans before and after consuming individually weight-dosed and calorically-matched ketone monoester or glucose drinks. Ketone monoester administration, but not glucose, significantly elevated cerebral antioxidants and energy markers while decreasing GABA, glutamate, and glutamine levels in the posterior cingulate cortex (PCC). Notably, increased bioenergetics, specifically an increase in total creatine, correlated with greater improvements in neural function as measured using rsfMRI. Our results integrate metabolic and functional neuroimaging findings, offering a comprehensive understanding of ketosis-induced changes in brain chemistry and functional network dynamics, yielding valuable insights into potential mechanisms by which ketosis imparts its neural benefits.

Adaptive optical correction in in vivo two-photon fluorescence microscopy with neural fields
Adaptive optics (AO) techniques are designed to restore ideal imaging performance by measuring and correcting aberrations originating from both the microscope system and the sample itself. Conventional AO methods require additional hardware, such as wavefront sensors and corrective devices, for aberration measurement and correction, respectively. These methods often necessitate microscopes to adhere to strict design parameters, like perfect optical conjugation, to ensure the accurate delivery of corrective patterns for wavefront correction using corrective devices. However, in general microscope systems, including commercially available ones, conjugation errors are more prone to arise due to incomplete conjugation among optical components by design and misalignment of the components, coupled with their limited access and adjustability, which hinders the rigorous integration of AO hardware. Here, we describe a general-purpose AO framework using neural fields, NeAT, that is applicable to both custom-built and commercial two-photon fluorescence microscopes and demonstrate its performance in various in vivo imaging settings. This framework estimates wavefront aberration from a single 3D two-photon fluorescence image stack, without requiring external datasets for training. Additionally, it addresses the issue of incomplete optical conjugation by estimating and correcting any conjugation errors, which enables more accurate aberration correction by the corrective device. Finally, it jointly recovers the sample's 3D structural information during the learning process, potentially eliminating the need for hardware-based AO correction. We first carefully assess its aberration estimation performance using a custom-built two-photon fluorescence microscope equipped with a wavefront sensor which provides the ground truth aberration for comparison. We further characterize and assess the robustness of the aberration estimation to image stacks with low signal-to-noise ratios, strong aberration, and motion artifacts. As practical applications, using a commercial microscope with a spatial light modulator, we first demonstrate NeAT's real-time aberration correction performance in in vivo morphological imaging of the mouse brain. We further show its performance in in vivo functional activity imaging of glutamate and calcium dynamics within the mouse brain.

Local postural changes elicit extensive and diverse skin stretch around joints, on the trunk, and the face
Skin stretch, induced by bodily movements, offers a potential source of information about the conformation of the body that can be transmitted to the brain via stretch-sensitive mechanoreceptive neurons. While previous studies have primarily focused on skin stretch directly at joints, here we investigate the extent and complexity of natural skin stretch across various body regions, including the face and trunk. We used a quad-camera setup to image large ink-based speckle patterns stamped on participants' skin and calculated the resulting stretch patterns on a millimeter scale during a range of natural poses. We observed that skin stretch associated with joint movement extends far beyond the joint itself, with knee flexion inducing stretch on the upper thigh. Large and uniform stretch patterns were found across the trunk, covering considerable portions of the skin. The face exhibited highly complex and non-uniform stretch patterns, potentially contributing to our capacity to control fine facial movements in the absence of traditional proprioceptors. Importantly, all regions demonstrated skin stretch in excess of mechanoreceptive thresholds, suggesting that behaviorally relevant skin stretch can occur anywhere on the body. These signals might provide the brain with valuable information about body state and conformation, potentially supplementing or even surpassing the capabilities of traditional proprioception.

Limitations of grouping subjects based on biological sex (males versus females) and a new approach: insights from intra-nucleus accumbens core dopamine-induced psychostimulant activity.
Background: In the field of substance use disorder research, sex-as-a-biological-variable (SABV) is employed to determine the mechanisms governing sex differences. Based on our recently developed MISSING (Mapping Intrinsic Sex Similarities as an Integral quality of Normalized Groups) model, we hypothesized that grouping subjects by biological sex does not represent the most effective way to group behavioral data objectively. To test our hypothesis, we conducted experiments to compare the psychostimulant effect of intra-nucleus accumbens (NAc) dopamine on groups based on 1) biological sex (current model) and 2) behavioral clustering (MISSING model) for effectiveness in identifying groups of subjects that a) are distinct with regards to behavioral variables, and b) confirm NAc dopamine neurochemical expression/activity topography (NEAT). Methods: For the current model, we separated subjects (n = 37 Sprague Dawley rats, male n = 20, female n = 17) by biological sex prior to all assessments. For the MISSING model, we conducted normal mixtures clustering of baseline activity, dopamine activity (as distance traveled in cm over 60 min) and dopamine activity normalized-to-baseline activity (NBA) of all subjects to identify behavioral clusters. Results: Separating groups by biological sex revealed groups (males and females) that were not clearly distinct with regards to behavioral variables and do not confirm NAc dopamine NEAT. Separating groups using the MISSING model revealed groups (behavioral clusters) that were clearly distinct with regards to behavior and confirm NAc dopamine NEAT. Conclusions: Our results reveal the limitations of grouping subjects based on biological sex. We discuss a new approach.