bioRxiv Subject Collection: Neuroscience's Journal

Properties of Alzheimers disease brain-derived tau aggregates define tau processing by human astrocytes.
The templated misfolding of tau proteins accounts for tau pathology spread in Alzheimers disease (AD). Post-translational modifications, including phosphorylation at specific residues, are closely linked with tau seeding ability and clinical disease progression. Increasing evidence supports a contributing role for astrocytes in tau spread. This study demonstrates that tau aggregates from postmortem AD brain are internalized and processed by human astrocytes. Differences in the efficiency of tau internalization, clearance and/or seeding were noted, which may reflect molecular properties of tau. Notably, we observed a direct relationship between alterations in tau handling by astrocytes and astrocyte responses, which were evident in transcriptomic data. Dysregulated genes include several previously identified as upregulated in reactive astrocytes in AD brain, as well as being implicated in pathological tau clearance by autophagy and other pathways. The study provides new insights into the complex interplay between tau molecular diversity and astrocyte responses in AD.

Single-shot detection of microscale tactile features
Tactile detection of very small features requires relative motion between the fingertip and a surface. The specific movement strategies that people use may be critical to maximize detection ability but little is known about the movement strategies people employ to support such detection. Here, human participants actively scanned a fingertip across a pair of silica wafers to detect which of the two contained a microscale feature (2, 6, and 10 m height and 525 m diameter). We constrained fingertip movement to ensure that participants would always contact the feature and would only contact the feature once. These procedures encouraged participants to use strategies that optimized detection rather than search and thus allowed us to more directly link movement strategies to detection. We also investigated the effects of fingertip movement direction and the finger used on detection. We found that participants were able to consistently detect microscale features as small as 2 m on the basis of a single contact event. The contact forces that participants used were substantially higher than those observed in previous studies focused on tactile search or geometric feature extraction. Scanning speeds were slower than those found during tactile search but faster than those reported during geometric feature extraction. Taken in conjunction with the associations between detection and finger used as well as scan direction, our results suggest that control and consistency of fingertip movement may be a primary consideration for movement strategies that optimize tactile detection.

Decoupling Coldness and Softness in Tactile Wetness Perception Using Tunable Hydrogels
This study investigates the perception of tactile wetness, a complex sensation experienced by humans. Previous research has primarily focused on either thermal or mechanical cues separately, or has used textiles as stimuli whose parameters are difficult to control. Here, we employed polyacrylamide hydrogels with varying stiffness levels soaked in liquids of distinct thermal conductivities. By psychophysically evaluating participants' perception of wetness, we showed that the wetness judgments for the samples exhibit a transitive relationship based on the mechanical and thermal cues from an intrinsically tunable organic material. We developed a prediction model of human wetness judgment with an accuracy of 90% and found that the best metrics for the most accurate model were those that were the most human-adjacent: change in temperature at the skin-sample interface (thermal) and compressive force from 2 mm indentation of the sample (mechanical). Given these parameters, we developed a perceptual space capable of recreating 7 distinct levels of wetness perception with the physical parameters used in this study. The results provide insights into the relative contributions of mechanical and thermal stimulus properties in wetness perception. Most notably, this work highlights that the physical characteristics of the skin-stimulus interface can provide ample information for creating a wetness perceptual space, as opposed to the chemical composition of the hydrogels.

Porphyromonas gingivalis outer membrane vesicles alter neuronal architecture and Tau phosphorylation in the embryonic mouse brain
Porphyromonas gingivalis (Pg) is an oral bacterial pathogen that has been associated with systemic inflammation and adverse pregnancy outcomes such as low birth weight and pre-term birth. Pg drives these sequalae through virulence factors decorating the outer membrane that are present on non-replicative outer membrane vesicles (OMV) that are suspected to be transmitted systemically. Given that Pg abundance can increase during pregnancy, it is not well known whether Pg-OMV can have deleterious effects on the brain of the developing fetus. We tested this possibility by treating pregnant C57/Bl6 mice with PBS (control) and OMV from ATCC 33277 by tail vein injection every other day from gestational age 3 to 17. At gestational age 18.5, we measured dam and pup weights and collected pup brains to quantify changes in inflammation, cortical neuron density, and Tau phosphorylated at Thr231. Dam and pup weights were not altered by Pg-OMV exposure, but pup brain weight was significantly decreased in the Pg-OMV treatment group. We found a significant increase of Iba-1, indicative of microglia activation, although the overall levels of IL-1{beta}, IL-6, TNF, IL-4, IL-10, and TGF{beta} mRNA transcripts were not different between the treatment groups. Differences in IL-1{beta}, IL-6, and TNF concentrations by ELISA showed IL-6 was significantly lower in Pg-OMV brains. Cortical neuron density was modified by treatment with Pg-OMV as immunofluorescence showed significant decreases in Cux1 and SatB2. Overall Thr231 was increased in pups exposed to Pg-OMV with the appearance of a secondary band of 60 kD. Together these results demonstrate that Pg-OMV can significantly modify the embryonic brain and suggests that Pg may impact offspring development via multiple mechanisms.

Sensory context of initiation-cue modulates action goal-relevant neural representations
The ability to produce goal-directed movement relies on the integration of diverse sources of sensory information specific to the task goal. Neural representations of goal-relevant features, such as target location and gaze direction, have been well studied in sensorimotor areas. It remains less clear whether goal-relevant motor representations are influenced by sensory changes to initiation-relevant information, such as a go-cue that provides no information about target location. We used Bayesian pattern component modelling of fMRI data during a delayed reach task with either visual or audiovisual go-cues to explore whether neural representations of goal-related features in sensorimotor areas are modulated by changes to initiation-relevant sensory information. We found that representations of target direction and gaze direction in the primary sensory areas, motor areas, and posterior parietal cortex, were sensitive to whether a reach was cued with a visual or audiovisual go-cue. These findings indicate that the central nervous system flexibly delegates the tasks of 'where' to move and 'when' to move based on available sensory context, even if initiation-relevant stimuli provide no additional information about target location.

Constructing well-defined neural networks of multiple cell types by picking and placing of neuronal spheroids using FluidFM
Controlled placement of single cells, spheroids and organoids is important for in vitro research, especially for bottom-up biology and for lab-on-a-chip and organ-on-a-chip applications. This study utilised FluidFM technology in order to automatically pick and place neuronal spheroids and single cells. Both single cells and spheroids of interest could be selected using light microscopy or fluorescent staining. A process flow was developed to automatically pick and pattern these neurons on flat surfaces, as well as to deposit them into polydimethylsiloxane microstructures on microelectrode arrays. It was shown that highly accurate and reproducible neuronal circuits can be built using the FluidFM automated workflow.

Brain-Body Interactions Influence the Transition from Mind Wandering to Awareness of Ongoing Thought
Our thoughts are inherently dynamic and often wander far from our current situation (mind wandering, MW). Although previous research revealed that the ascending arousal system shapes neural dynamics to mediate awareness of ongoing thoughts, the physiological states and afferent signals altered by this activation and its effects on awareness are unknown. In this study, we examined electroencephalography (EEG), electrocardiography (ECG), and respiration data before participants were aware of MW during a task in which they focused on external or internal stimuli. We showed that the transition from MW to awareness was characterized by decreased alpha and beta activity and increased heartbeat-evoked potential (HEP) amplitudes. In addition, the participants were more likely to be in the exhalation phase becoming aware, and in the inhalation phase at the time of MW reports. Moreover, changes in cardiac activity and HEP accompanied this pattern when participants were asked to focus on respiration. Based on these findings, we suggest that the release from the increased cognitive load with sustained MW and catching these changes as physiological alterations supporting awareness of MW; moreover, the modulation of the respiratory cycle by focusing on breathing enhances these changes.

Circuit function is more robust to changes in synaptic than intrinsic conductances
Circuit function results from both intrinsic conductances of network neurons and the synaptic conductances that connect them. In models of neural circuits, different combinations of maximal conductances can give rise to similar activity. We compared the robustness of a neural circuit to changes in their intrinsic versus synaptic conductances. To address this, we performed a sensitivity analysis on a population of conductance-based models of the pyloric network from the crustacean stomatogastric ganglion (STG). The model network consists of three neurons with nine currents: a sodium current (Na), three potassium currents (Kd, KCa, A-type), two calcium currents (CaS and CaT), a hyperpolarization-activated current (H), a non-voltage-gated leak current (leak), and a neuromodulatory current (MI). The model cells are connected by seven synapses of two types, glutamatergic and cholinergic. We produced one hundred models of the pyloric network that displayed similar activities with values of maximal conductances distributed over wide ranges. We evaluated the robustness of each model to changes in their maximal conductances. We found that individual models have different sensitivities to changes in their maximal conductances, both in their intrinsic and synaptic conductances. As expected the models become less robust as the extent of the changes increase. Despite quantitative differences in their robustness, we found that in all cases, the model networks are more sensitive to the perturbation of their intrinsic conductances than their synaptic conductances.

Immediate Modulation of the Blood Oxygenation Level-Dependent Signals by Dual-Site Transcranial Alternating Current Stimulation Propagates Across the Whole Brain
Transcranial alternating current stimulation (tACS) is assumed to target specific brain regions and modulate their activity. Recent discussions of tACS propose that, entraining the phase of brain activity to the stimulation current, stimulation effects extend globally across the whole brain based on phase differences. However, immediate online spatiotemporal propagation of resting-state blood oxygenation level-dependent (BOLD) signals within the brain due to multi-region stimulation remains unclear. The objectives of the present study were three-fold: 1) to elucidate the immediate online effect of tACS on BOLD signal, 2) to examine the extent of the influence on the brain when applying tACS, and 3) to explore whether variations in the phase difference between two brain regions result in differential effects on the stimulated areas and the whole brain. Through two experiments involving high-definition tACS with simultaneous measurements using a functional magnetic resonance imaging (fMRI), we revealed that the immediate online stimulation effects not only altered BOLD signals in the stimulated regions but also propagated across the whole brain in specific spatiotemporal patterns (functional networks). Stimulation effects were observed specifically in regions rich in neural fibres, including the grey and white matter, with no effect in regions containing cerebrospinal fluid. The timing of the signal value peaks depended on the stimulated region and functional networks, with a notable trend observed. Thus, tACS with a specific phase difference in two anatomically connected brain regions can immediately modulate online neural dynamics at both local and global scales.

Graphical abstract

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Policy shaping based on the learned preferences of others accounts for risky decision-making under social observation
Observing others choices influences individuals decisions, often leading them to follow others. However, it is repeatedly reported that being observed by others tends to make people act more riskily. We hypothesized that this discrepancy arises from individuals belief that others prefer riskier choices than they do. To examine this hypothesis, we used a gambling task where on some trials, individuals were informed that their choices would be observed by a risk- averse or seeking partner. Most important, individuals were given chances to learn each partners preference beforehand. As expected, individuals initially believed that partners would make relatively riskier choices than they would. Against two alternative explanations, we found that individuals simulated partners choices and weighed these simulated choices in making their own choices. Using functional magnetic resonance imaging, we showed that decision probabilities adjusted with the simulated partners choices were represented in the temporoparietal junction (TPJ). Moreover, individual differences in the functional connectivity between the TPJ and the medial prefrontal cortex (mPFC) were explained by the interaction between model-estimated social reliance and sensitivity to social cues in the mPFC. These findings provide a neuromechanistic account of how being observed by others affects individuals decision-making, highlighting the roles of the mPFC and TPJ in simulating social contexts based on individuals beliefs.

Serial Two-Photon Tomography Imaging of the whole marmoset brain for neuroanatomical analyses
Serial Two photon tomography (STPT) imaging is a technique to image a mass of tissue in its three-dimensional shape by combining two-photon imaging with automatic stage control and microtome slicing. We successfully implemented this technique for tracing the axonal projections in the marmoset brain. Here we describe the detailed experimental procedures that realized reliable volumetric imaging of the whole marmoset brain. We also introduce auxiliary histological techniques including visualization of myelin structure by simple light reflection, and immunological detection of non-fluorescent anterograde and retrograde tracers, which further enhance the utility of STPT data.

A flexible high-precision photoacoustic retinal prosthesis
Retinal degenerative diseases of photoreceptors are a leading cause of blindness with no effective treatment. Retinal prostheses seek to restore sight by stimulating remaining retinal cells. We here present a photoacoustic retinal stimulation technology. We designed a polydimethylsiloxane and carbon-based flexible film that converts near-infrared laser pulses into a localized acoustic field, aiming at high-precision acoustic activation of mechanosensitive retinal cells. This photoacoustic stimulation of wild-type and degenerated ex vivo retinae resulted in robust and localized retinal ganglion cell activation with sub-100-{micro}m resolution in both wild-type and degenerated ex vivo retinae. Our millimeter-size photoacoustic film generated neural activation in vivo along the visual pathway to the superior colliculus, as measured by functional ultrasound imaging when the film was implanted in the rat subretinal space and stimulated by pulsed laser. Biosafety of the film was indicated by absence of short-term adverse effect under optical coherence tomography retinal imaging, while local thermal increase was measured below 1 {degrees}C. These findings demonstrate the potential of our photoacoustic stimulation for visual restoration in blind patients with a high spatial precision and a large field of view.

DIFFERENTIAL CONTRIBUTIONS OF THE SPECTRO-TEMPORAL AND VOCAL CHARACTERISTICS OF AUDITORY PSEUDOWORDS TO MULTIPLE SOUND-SYMBOLIC MAPPINGS
Sound symbolism, the idea that the sound of a word alone can convey its meaning, is often studied using auditory pseudowords. For example, people reliably assign the auditory pseudowords "bouba" and "kiki" to rounded and pointed shapes, respectively. Previously we showed that representational dissimilarity matrices (RDMs) of the shape ratings of auditory pseudowords correlated significantly with RDMs of acoustic parameters reflecting spectro-temporal variations; the ratings also correlated significantly with voice quality features. Here, participants rated auditory pseudowords on scales representing categorical opposites across seven meaning domains, including shape. Examination of the relationships of the perceptual ratings to spectro-temporal and vocal parameters of the pseudowords essentially replicated our previous findings for shape while varying patterns emerged for the other domains. Thus, the spectro-temporal and vocal properties of spoken pseudowords contribute differentially to sound-symbolic mapping depending on the meaning domain.

Peripheral Inflammation is accompanied by Cerebral Hypoperfusion in Mice
Introduction: Chronic pain is a disabling condition that is accompanied by neuropsychiatric comorbidities such as anxiety, depression, and cognitive decline. While the peripheral alterations are well-studied, we lack an understanding of how these peripheral changes can result in long-lasting brain alterations and the ensuing behavioral phenotypes. This study aims to quantify changes in cerebral blood perfusion using laser speckle contrast imaging (LSCI) in the murine Complete Freunds adjuvant (CFA) model of unilateral peripheral inflammation. Methods: Twenty female and 24 male adult C57BL/6 mice were randomly assigned to control (0.05ml saline) or 1 of 3 experimental groups receiving CFA (0.01ml, 0.05ml, and 0.1ml) on the right hindpaw. Three days after the intraplantar injections, animals were assessed for signs of pain (von Frey), working memory (y-maze), and anxiety (zero maze and open field), and subjected to craniotomy and in vivo LSCI of the parietal-temporal lobes. Results: Unilateral administration of CFA resulted in signs of local inflammation, decreased mechanical thresholds on the affected hindpaw, signs of anxiety in the zero maze, as well as cerebral hypoperfusion in dose-dependent manner. Discussion: To our knowledge, this is the first study using laser speckle contrast imaging to examine the effects of CFA-induced peripheral inflammation on cerebral blood perfusion. It serves as a first step in delineating the path by which insult to peripheral tissues can cause long-lasting brain plasticity via vascular mechanisms.

Oxytocin salvages context-specific hyperaltruistic preference through moral framing
An intriguing advancement in recent moral decision-making research suggests that people are more willing to sacrifice monetary gains to spare others from suffering than to spare themselves, yielding a hyperaltruistic tendency. Other studies, however, indicate an opposite egoistic bias in that subjects are less willing to harm themselves for the benefits of others than for their own benefits. These results highlight the delicate inner workings of moral decision and call for a mechanistic account of hyperaltruistic preference. We investigated the boundary conditions of hyperaltruism by presenting subjects with trade-off choices combing monetary gains and painful electric shocks, or, choices combing monetary losses and shocks. We first showed in study 1 that switching the decision context from gains to losses effectively eliminated the hyperaltruistic preference and the decision context effect was associated with the altered relationship between subjects instrumental harm (IH) trait attitudes and their relative pain sensitivities. In the pre-registered study 2, we tested whether oxytocin, a neuropeptide linked to parochial altruism, might salvage the context-dependent hyperaltruistic preference. We found that oxytocin increased subjects reported levels of framing the task as harming (vs. helping) others, which mediated the correlation between IH and relative pain sensitivities. Thus, the loss decision context and oxytocin nullified and restored the mediation effect of subjective harm framing, respectively. Our results help to elucidate the psychological processes underpinning the contextual specificity of hyperaltruism and carry implications in promoting prosocial interactions in our society.

Computer vision guided rapid and precise automated cranial microsurgeries in rodents
Neuroscientists employ various experimental procedures to interface with the brain to study and perturb the neural activity during behavior. A common procedure that allows such physical interfacing is cranial microsurgery, wherein small to large craniotomies are performed in the overlying skull for insertion of neural interfaces or implantation of optically clear windows for long-term cranial observation. Performing craniotomies is, however, a skilled task that requires significant time and practice and further needs to be carried out precisely to ensure that the procedure does not cause damage to the underlying brain and dura. Here, we present a computer vision-guided craniotomy robot (CV-Craniobot) that utilizes machine learning to accurately estimate the dorsal skull anatomy from optical coherence tomography (OCT) images. Instantaneous information of the skull morphology is used by a robotic mill to rapidly and precisely remove the skull from a desired craniotomy location. We show that the CV-Craniobot can perform small (2 - 4 mm diameter) craniotomies with near 100% success rates within 2 minutes and large craniotomies encompassing most of the dorsal cortex in less than 5 minutes. Thus, the CV-Craniobot enables rapid and precise craniotomies, significantly reducing surgery time as compared to human practitioners and eliminating the need for long training.

Nonlinear dendritic integration supports Up-Down states in single neurons
Changes in the activity profile of cortical neurons are due to phenomena at the scale of local and long-range networks. Accordingly, the often abrupt transitions in the state of cortical neurons - a phenomenon known as Up-Down states - are attributed to variations in the afferent neurons' activity. However, cellular physiology and morphology may also play a role. This study examines the impact of dendritic nonlinearities, in the form of voltage-gated NMDA receptors, on the response of cortical neurons to balanced excitatory/inhibitory synaptic inputs. Using a neuron model with two segregated dendritic compartments, we compare cells with and without dendritic nonlinearities. Our analysis shows that NMDA receptors boost somatic firing in the balanced condition and increase the correlation of membrane potentials across the three compartments of the neuron model. Then, we introduce controlled fluctuations in excitatory inputs and quantify the ensuing bimodality of the somatic membrane potential. We show that dendritic nonlinearities are crucial for detecting these fluctuations and initiating Up-Down states whose shape and statistics closely resemble electrophysiological data. Our results provide new insights into the mechanisms underlying cortical bistability and highlight the complex interplay between dendritic integration and network dynamics in shaping neuronal behavior.

Using TMS-EEG to study the intricate interplay between GABAergic inhibition and glutamatergic excitation during reactive and proactive motor inhibition
Background: Combining Transcranial magnetic stimulation (TMS) with electroencephalography (EEG) enables assess TMS-evoked potentials (TEP) and estimate {gamma}-aminobutyric acid (GABA) and glutamatergic neurotransmission across the entire motor inhibition network. The N45 and N100 TEP peaks are associated with GABAa and GABAb signaling, respectively, whereas the N15, P30 and P60 TEPs reflect glutamatergic neurotransmission. This study applied TMS-EEG to investigate modulation of TEP components during reactive and proactive inhibition and whether individual differences in GABA and glutamate signaling predict inhibitory performance. Methods: Twenty-four healthy participants completed two TMS-EEG sessions, targeting either the left primary motor cortex (M1) or the pre-supplementary motor area (preSMA) at rest and during a stop-signal task. We compared TEP peak amplitudes across TMS (active/sham) and Trial Type (stop/go trials) and assessed their relationship with task performance. Results: Participants with a higher N45 amplitude at rest over M1, reflecting increased GABAa signaling, demonstrated a faster stop-signal reaction time. TMS during motor inhibition revealed higher N15 amplitudes over preSMA, reflecting increased glutamatergic neurotransmission, for successful stops versus go trials. Similarly, N15 was higher for uncertain than certain go trials suggesting that an early excitatory signal from preSMA is crucial for both reactive and proactive motor inhibition. Conclusion: Higher GABAa inhibitory signaling in M1 at rest is linked to faster reactive inhibition. The preSMA likely plays a key role in both reactive and proactive motor inhibition. Here we provide novel direct empirical insights into the underlying neurophysiological mechanisms, highlighting a functional relevance of early glutamatergic excitatory signals for successful motor inhibition.

Hippocampal neuronal activity is aligned with action plans
Neurons in the hippocampus are correlated with different variables, including space, time, sensory cues, rewards, and actions, where the extent of tuning depends on ongoing task demands. However, it remains uncertain whether such diverse tuning corresponds to distinct functions within the hippocampal network or if a more generic computation can account for these observations. To disentangle the contribution of externally driven cues versus internal computation, we developed a task in mice where space, auditory tones, rewards, and context were juxtaposed with changing relevance. High-density electrophysiological recordings revealed that neurons were tuned to each of these modalities. By comparing movement paths and action sequences, we observed that external variables had limited direct influence on hippocampal firing. Instead, spiking was influenced by online action plans modulated by goal uncertainty. Our results suggest that internally generated cell assembly sequences are selected and updated by action plans toward deliberate goals. The apparent tuning of hippocampal neuronal spiking to different sensory modalities might emerge due to alignment to the afforded action progression within a task rather than representation of external cues.

Dissociable dynamic effects of expectation during statistical learning.
The brain is thought to generate internal predictions, based on previous statistical regularities in the environment, to optimise behaviour. Predictive processing has been repeatedly demonstrated and seemingly explains expectation suppression (ES), or the attenuation of neural activity in response to expected stimuli. However, the mechanisms behind ES are unclear and various models of the mechanisms supporting ES have been suggested with conflicting evidence. Sharpening models propose that expectations suppress neurons that are not tuned to the expected stimulus, increasing the signal-to-noise ratio for expected stimuli. In contrast, dampening models posit that expectations suppress neurons that are tuned to the expected stimuli, increasing the relative response amplitude for unexpected stimuli. Previous studies have used decoding analyses to examine these effects, with increases in decoding accuracy interpreted in terms of sharpening and decreases related to dampening. The opposing process theory (OPT) has suggested that both processes may occur at different time points, namely that initial sharpening is followed by later dampening of the neural representations of the expected stimulus as learning progresses. In this study we aim to test this theory and shed light on the dynamics of expectation effects, both at single trial level and over time. Thirty-one participants completed a statistical learning task consisting of paired scene categories whereby a 'leading' image from one category is quickly followed by a 'trailing' image from a different category. Multivariate EEG analyses focussed on decoding stimulus information related to the trailing image category. Within-trial, decoding analyses showed that stimulus expectation increased decoding accuracy at early latencies and decreased decoding accuracy at later latencies, in line with OPT. However, across trials, stimulus expectation decreased decoding accuracy in initial trials and increased decoding accuracy in later trials. We theorise that these dissociable dynamics of expectation effects within and across trials can be explained in the context of hierarchical learning mechanisms. Our single trial results provide evidence for the OPT, while our results over time suggest that sharpening and dampening effects emerge at different stages of learning.

A hypothalamus-brainstem circuit governs the prioritization of safety over essential needs
Animals continously adapt their behavior to balance survival and fulfilling essential needs. This balancing act involves prioritization of safety over the pursuit of other needs. However, the specific deep brain circuits that regulate safety-seeking behaviors in conjuction with motor circuits remain poorly understood. Here we identify a class of glutamatergic neurons in the lateral hypothalamic area (LHA) that target the midbrain locomotor-promoting pedunculopontine nucleus (PPN). Upon activation, this LHA-PPN pathway orchestrates context-dependent locomotion, prioritizing safety-directed movement over other essential needs such as foraging or mating. Remarkably, the neuronal activity of these circuits correlates directly with safety-seeking behavior. These circuits may respond to both intrinsic and external cues, playing a pivotal role in ensuring survival. Our findings uncover a circuit motif within the lateral hypothalamus that when recruited, prioritizes critical needs through the recruitment of an appropriate motor action.

Deciphering the nanoscale architecture of presynaptic actin using a micropatterned presynapse-on-glass model
Chemical synapses are fundamental units for the transmission of information throughout the nervous system. The cytoskeleton allows to build, maintain and transform both pre- and postsynaptic contacts, yet its organization and the role of its unique synaptic nanostructures are still poorly understood. Here we present a presynapse-on-glass model where presynaptic specializations are robustly induced along the axons of cultured neurons by micropatterned dots of neuroligin, allowing the controlled orientation and easy optical visualization of functional induced presynapses. We demonstrate the relevance and usefulness of this presynapse-on-glass model for the study of presynaptic actin architecture, showing that a majority of induced presynapses are enriched in actin, with this enrichment being correlated to higher synaptic cycling activity. We confirm our previous results on bead-induced presynapses by identifying the same distinct actin nanostructures within presynapses: corrals, rails and mesh. Furthermore, we leverage the controlled orientation of the presynapse-on-glass model, visualizing the arrangement of these actin structures relative to the active zone nanoclusters using multicolor 3D Single Molecule Localization Microscopy (SMLM), and relative to the sub-diffractive localization exocytic events using a correlative live-cell and SMLM approach.

Functional Roles of Sensorimotor Alpha and Beta Oscillations in Overt Speech Production
Power decreases, or desynchronization, of sensorimotor alpha and beta oscillations (i.e., alpha and beta ERD) have long been considered as indices of sensorimotor control in overt speech production. However, their specific functional roles are not well understood. Hence, we first conducted a systematic review to investigate how these two oscillations are modulated by speech motor tasks in typically fluent speakers (TFS) and in persons who stutter (PWS). Eleven EEG/MEG papers with source localization were included in our systematic review. The results revealed consistent alpha and beta ERD in the sensorimotor cortex of TFS and PWS. Furthermore, the results suggested that sensorimotor alpha and beta ERD may be functionally dissociable, with alpha related to (somato-)sensory feedback processing during articulation and beta related to motor processes throughout planning and articulation. To (partly) test this hypothesis of a potential functional dissociation between alpha and beta ERD, we then analyzed existing intracranial electroencephalography (iEEG) data from the primary somatosensory cortex (S1) of picture naming. We found moderate evidence for alpha, but not beta, ERD's sensitivity to speech movements in S1, lending supporting evidence for the functional dissociation hypothesis identified by the systematic review.

Widespread Associations between Behavioral Metrics and Brain Microstructure in ASD
Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by deficits in social communication and repetitive behaviors. A diagnosis of ASD is provided by a clinician following cognitive and behavioral evaluations, but there is currently no biomarker associating these metrics with neurological changes. Our lab has previously found that g-ratio, the proportion of axon width to myelin diameter, and axonal conduction velocity, which is associated with the capacity of an axon to carry information, are both decreased in ASD individuals. By associating these differences with performance on cognitive and behavioral tests, we can evaluate which tests most reveal changes in the brain. Analyzing 273 participants (148 with ASD) ages 8-to-17 (49% female) through an NIH-sponsored Autism Centers of Excellence (ACE) network (Grant#: MH100028), we observe widespread associations between behavioral and cognitive evaluations of autism and between behavioral and microstructural metrics. Analyzing data from all participants, conduction velocity but not g-ratio was significantly associated with many behavioral metrics. However, this pattern was reversed when looking solely at ASD participants. This reversal may suggest that the mechanism underlying differences between autistic and non-autistic individuals may be distinct from the mechanism underlying ASD behavioral severity. Two additional machine learning cluster analyses applied to neuroimaging data reinforce the association between neuroimaging and behavioral metrics and suggest that age-related maturation of brain metrics may drive changes in ASD behavior. By associating neuroimaging metrics with ASD, it may be possible to measure and identify individuals at high risk of ASD before behavioral tests can detect them. Significance Statement: This study establishes numerous relationships between multiple behavioral, language, and social metrics in ASD. Subsequently, this study is the first to then show associations between diffusion microstructure and subscales of behavioral assessments. Limited associations of these behaviors with conduction velocity may indicate that axonal diameter is a predominating factor in characterizing ASD over other metrics, such as myelination, however within ASD subjects the g-ratio is more closely related to behavioral metrics, suggesting a potential role for myelination in ASD severity. These findings suggest that some subscales and metrics more accurately capture behaviors associated neurologically with ASD than others, including composite scores, demonstrating the potential to identify children at high risk for ASD at an earlier age.

Neuropathic pain and distinct CASPR2 autoantibody IgG subclasses drive neuronal hyperexcitability
Patients with autoantibodies (aAbs) against the contactin-associated protein-like 2 (CASPR2) suffer from a variety of clinical syndromes including neuropathic pain, in some patients even as the only symptom. CASPR2 is an adhesion protein of the neurexin IV family and part of the voltage-gated potassium channel complex (VGKC) in neurons of dorsal root ganglia (DRG). The subsequent pathological mechanisms following the binding of CASPR2 aAbs and their association with pain are only partially understood. CASPR2 aAbs are mainly of the IgG4 subclass. Previous studies have neglected subclass- dependent effects. Here we investigated 49 subclassified patient serum samples positive for CASPR2 aAbs. To unravel underlying molecular mechanisms, we used a combination of super-resolution lattice structural illumination microscopy (SIM2) and functional readouts by calcium imaging and electrophysiological recordings. CASPR2-positive patient sera subclassified in IgG4 together with at least one other IgG subclass (IgGX) and patients with only IgG4 were further subdivided into the pain and no pain group. Patient subclassification shed further light on the pathological mechanisms of CASPR2 aAbs. A decrease of CASPR2 expression after long-term exposure to CASPR2 aAbs was only observed for the patient group without pain. Upon withdrawal of the CASPR2 aAbs, CASPR2 expression returned to normal level. Structural alterations were obtained by increased distances between CASPR2 and associated potassium channels along DRG axons using high-resolution lattice SIM2 microscopy but only following binding of CASPR2 aAbs from patients with pain. Similarly, CASPR2 aAbs of patients with pain significantly increased overall neuronal excitability of cultured DRG neurons as measured by calcium imaging. Patch-clamp recordings revealed significantly decreased current amplitudes of voltage-gated potassium (Kv) channels after incubation with all four CASPR2 aAbs subclassifications with the most prominent effect of serum samples harboring IgG4 aAbs. Notably, a patient serum sample lacking IgG4 did not alter Kv channel function. Withdrawal of aAbs rescued Kv channel function to normal levels suggesting that the affected potassium channel function is rather due to a functional block of the VGKC rather than altered structural integrity of the VGKC. Taken together, we found IgG4 aAbs to be a major modifier of potassium channel function. The increase in DRG excitability is primarily due to impaired Kv channel conductance as a consequence of CASPR2 aAbs binding but additional and so far unidentified signal pathways contribute to this process in patients with neuropathic pain.

Motor learning is regulated by GDNF levels in postnatal cerebellar Purkinje cells
Purkinje cells, the sole output neurons of the cerebellar cortex, are crucial for cerebellum-dependent motor learning. Previously we demonstrated that a ubiquitous 2-3-fold increase of endogenous glial cell line-derived neurotrophic factor (GDNF) improves motor learning. However, GDNF impacts many organ systems and cell types throughout the body leaving the underlying mechanism elusive. Here, we utilize an innovative conditional GDNF Hypermorphic mouse model to show that a 2-fold increase in endogenous GDNF specifically in postnatal Purkinje cells (PCs) is sufficient to enhance motor learning in adult animals. We demonstrate that improved motor learning is associated with increased glutamatergic input to PCs and elevated spontaneous firing rate of these cells, opposite to cerebellar ataxia where reduction in motor function and learning associates with decreased spontaneous activity of PCs. Notably, the GDNF expression levels variation range studied in our mouse model's cerebellum falls within the normal range of variation observed in healthy human cerebellums. Our findings uncover a molecular pathway and a specific cell type that regulate motor learning, potentially explaining some individual differences in human motor skill acquisition.

Adiponectin signaling modulates fat taste responsiveness in mice
We previously reported that the adiponectin receptor agonist AdipoRon selectively enhances cellular responses to fatty acids in a human taste cell line. The enhancement role of AdipoRon on fatty acid-induced cell responses is mediated by the activation of AMPK and translocation of CD36 on human taste cells. It has also been shown that adiponectin selectively increases taste behavioral responses to intralipid in mice. However, the molecular mechanism underlying the physiological effects of adiponectin on fat taste in mice remains unclear. Here we define AdipoR1 as the mediator responsible for the enhancement role of adiponectin/AdipoRon on fatty acid-induced responses in mouse taste bud cells. Calcium imaging data demonstrate that AdipoRon enhances linoleic acid-induced calcium responses in a dose-dependent fashion in mouse taste cells isolated from circumvallate and fungiform papillae. Similar to the human taste cells, the enhancement role of AdipoRon on fatty acid-induced responses was impaired by the co-administration of an AMPK inhibitor (Compound C) or a CD36 inhibitor (SSO). Utilizing Adipor1-deficient animals we determined the enhancement role of AdipoRon/adiponectin is dependent on AdipoR1 since AdipoRon/adiponectin failed to increase fatty acid-induced calcium responses in taste bud cells isolated from these mice. Brief-access taste tests were performed to determine whether AdipoRon's enhancement role was correlated with any differences in taste behavioral responses to fat. Although AdipoRon enhances the cellular responses of taste bud cells to fatty acids, it does not appear to alter fat taste behavior in mice. However, fat naive Adipor1-/- animals were indifferent to increasing concentrations of intralipid, suggesting that adiponectin signaling may have profound effects on the ability of mice to detect fatty acids in the absence of previous exposure to fatty acids and fat-containing diets.

DNMT1-Mediated Regulation of Inhibitory Interneuron Migration Impacts Cortical Architecture and Function
The fine-tuned establishment of neuronal circuits during the formation of the cerebral cortex is pivotal for its functionality. Developmental abnormalities affecting the composition of cortical circuits, which consist of excitatory neurons and inhibitory interneurons, are linked to a spectrum of neuropsychiatric disorders. Excitatory neurons originate in cortical proliferative zones, while inhibitory interneurons migrate from discrete domains of the basal telencephalon into the cortex. This migration is intricately governed by intrinsic genetic programs and extrinsic cues. Our current study reveals the role of the DNA methyltransferase 1 (DNMT1) in controlling expression of key genes implicated in mouse cortical interneuron development and in guiding the migration of somatostatin-expressing interneurons within the developing cortex. Dnmt1 deletion causes interneurons to exit prematurely from the superficial migratory stream. In addition to the perturbed migration pattern and altered gene expression signatures, Dnmt1-deficient interneurons had a discernible non-cell autonomous effect on cortical progenitors, which culminated in nuanced alterations of layer thicknesses in the adult cortex. Our study reveals that an epigenetic mechanism governs the migration of cortical interneurons and through this, their instructive role in sculpting the intricate cortical layer architecture by signaling to cortical progenitors, with pronounced effects on cortical network function.

Interhemispheric CA1 projections support spatial cognition and are affected in a mouse model of the 22q11.2 deletion syndrome
Untangling the hippocampus connectivity is critical for understanding the mechanisms supporting learning and memory. However, the function of interhemispheric connections between hippocampal formations is still poorly understood. So far, two major hippocampal commissural projections have been characterized in rodents. Mossy cells from the hilus of the dentate gyrus project to the inner molecular layer of the contralateral dentate gyrus and CA3 and CA2 pyramidal neuron axonal collaterals to contralateral CA3, CA2 and CA1. In contrary, little is known about commissural projection from the CA1 region. Here, we show that CA1 pyramidal neurons from the dorsal hippocampus project to contralateral dorsal CA1 as well as dorsal subiculum. We further demonstrate that the interhemispheric projection from CA1 to dorsal subiculum supports spatial memory and spatial working memory in WT mice, two cognitive functions impaired in male mice from the Df16(A)+/- model of 22q11.2 deletion syndrome (22q11.2DS) associated with schizophrenia. Investigation of the CA1 interhemispheric projections in Df16(A)+/- mice revealed that these projections are disrupted with male mutants showing stronger anatomical defects compared to females. Overall, our results characterize a novel interhemispheric projection from dCA1 to dorsal subiculum and suggest that dysregulation of this projection may contribute to the cognitive deficits associated with the 22q11.2DS.

Endocytic BDNF secretion through extracellular vesicle-dependent secretory pathways in astrocytes
Brain-derived neurotrophic factor (BDNF) plays an essential role in regulating diverse neuronal functions in an activity-dependent manner. Although BDNF is synthesized primarily in neurons, astrocytes can also supply BDNF through various routes, including the recycling of neuron-derived BDNF. Despite accumulating evidence for astrocytic BDNF uptake and resecretion of neuronal BDNF, the detailed mechanisms underlying astrocytic BDNF recycling remain unclear. Here, we report that astrocytic resecretion of endocytosed BDNF is mediated by an extracellular vesicle (EV)-dependent secretory pathway. In cultured primary astrocytes, extracellular BDNF was endocytosed into CD63-positive EVs, and stimulation of astrocytes with ATP could evoke the release of endocytosed BDNF from CD63-positive vesicles. Downregulation of vesicle-associated membrane protein 3 (Vamp3) led to an increase in the colocalization of endosomal BDNF and CD63 but a decrease in extracellular vesicle release, suggesting the necessity of Vamp3-dependent signaling for EV-mediated BDNF secretion. Collectively, our findings demonstrate that astrocytic recycling of neuronal BDNF is dependent on the EV-mediated secretory pathway via Vamp3-associated signaling.