bioRxiv Subject Collection: Neuroscience's Journal

Superoxide enters neurons via LRRC8A-containing volume-regulated anion channels
Superoxide (O2-) is both an intercellular signaling molecule and a cause of neuronal oxidative stress. Superoxide entry into neurons is thought to be indirect, requiring its dismutation to nonpolar hydrogen peroxide. Here we show instead that superoxide enters neurons directly, via LRRC8A-containing volume-sensitive organic anion channels. In primary cultures, neuronal oxidative stress induced either by NMDA receptor stimulation or exposure to authentic superoxide was blocked by the anion channel blockers DIDS and DCPIB and by LRRC8A gene disruption. In mouse cortex, neuronal oxidative stress induced by either NMDA injection or transient ischemia was likewise blocked by both DCPIB and LRRC8A gene disruption. These findings identify a role for LRRC8A-containing volume-sensitive organic anion channels in neuronal oxidative signaling, stress, and glutamate excitotoxicity.

Normative and individual, non-normative intrinsic networks and the transition to impaired cognition
Despite their temporal lobe pathology, a significant subgroup of temporal lobe epilepsy (TLE) patients are able to maintain normative cognitive functioning. Here, we identify TLE patients with intact versus impaired cognitive profiles, and interrogate for the presence of both normative and highly individual intrinsic connectivity networks(ICN) all towards understanding the transition from impaired to intact neurocognitive status. We retrospectively investigated data from 88 TLE patients and matched 91 healthy controls with resting-state functional MRI. Functional MRI data were decomposed using independent component analysis to obtain individualized ICNs. Here, we calculated the degree of match between individualized ICNs and canonical ICNs (e.g., Yeo et.al 17 resting-state network) and divided each participant's ICNs into normative or non-normative status based on the degree of match. We found that the individualized networks matched the canonical networks less well in the cognitively impaired compared to the cognitively intact TLE patients. The cognitively impaired patients showed significant abnormalities in the profiles of both normative and non-normative networks, whereas the intact patients showed abnormalities only in non-normative networks. At the same time, we found normative networks held a strong, positive association with the neuropsychological measures, with this association negative in non-normative networks. We were able to provide the initial data demonstrating that significant cognitive deficits are associated with the status of highly-individual ICNs, making clear that the transition from intact to impaired cognitive status is not simply the result of disruption to normative brain networks.

Feature selectivity of corticocortical feedback along the primate dorsal visual pathway
Anatomical studies have revealed a prominent role for feedback projections in the primate visual cortex. Theoretical models suggest that these projections support important brain functions, like attention, prediction, and learning. However, these models make different predictions about the relationship between feedback connectivity and neuronal stimulus selectivity. We have therefore performed simultaneous recordings in different regions of the primate dorsal visual pathway. Specifically, we recorded neural activity from the medial superior temporal (MST) area, and one of its main feedback targets, the middle temporal (MT) area. We estimated functional connectivity from correlations in the single-neuron spike trains and performed electrical microstimulation in MST to determine its causal influence on MT. Both methods revealed that inhibitory feedback occurred more commonly when the source and target neurons had very different stimulus preferences. At the same time, the strength of feedback suppression was greater for neurons with similar preferences. Excitatory feedback projections, in contrast, showed no consistent relationship with stimulus preferences. These results suggest that corticocortical feedback could play a role in shaping sensory responses according to behavioral or environmental context.

Graph analysis of the guilt network highlights associations with subclinical anxiety and self-blame
Maladaptive forms of guilt, such as excessive self-blame, are common characteristics of anxiety disorders. The associated network includes the superior anterior temporal lobe (sATL), underlying the conceptual representations of social meaning, and fronto-subcortical areas involved in the affective dimension of guilt. Nevertheless, despite understanding the anatomy of the guilt processing circuitry, network-level changes related to subclinical anxiety and self-blaming behaviour have not been depicted. To fill this gap, we used graph theory analyses on a resting-state functional and diffusion-weighted magnetic resonance imaging dataset of 78 healthy adults. Within the guilt network, we found increased functional contributions (higher clustering coefficient, local efficiency and strength) of the left sATL for individuals with higher self-blaming and trait-anxiety, while functional isolation (lower clustering coefficient and local efficiency) of the left pars opercularis and insula was related to higher trait-anxiety. Trait-anxiety was also linked to the structural network's global parameters (mean clustering coefficient), with the circuitry's architecture favouring increased local information processing in individuals with increased anxiety levels. Previous research suggests that aberrant interactions between conceptual (sATL) and affective (fronto-limbic) regions underlie maladaptive guilt and the current results align and expand on this theory by detailing network changes associated with self-blame and trait-anxiety.

Gustatory-neuron-supplied R-spondin-2 is required for taste bud replenishment
Taste buds undergo continuous cell turnover throughout life, and taste cell replenishment relies strictly on innervation, a phenomenon first described almost 150 years ago. Recently, we provided evidence that R-spondin 2 (Rspo2) may be the long-sought gustatory neuron-supplied factor that regulates taste stem cell activity, via its interaction with taste stem/progenitor cell-expressed receptor Rnf43/Znrf3. Yet, whether gustatory-neuron-supplied Rspo2 is strictly required for taste tissue maintenance has not been resolved. Here, we set out to determine the necessity of gustatory-neuron-supplied Rspo2 in taste tissue homeostasis using genetic approaches. We used a mouse line that harbors the neomycin-resistance gene (NeoR) in one of the intron regions of the Rspo2 gene, which results in reduced expression of Rspo2. The number of taste buds is significantly reduced in these mice, compared to wild-type mice, in both anterior and posterior tongue. This phenotypic change was completely reversed by removing NeoR from the Rspo2 gene, thus making it normal. We also combined adeno-associated virus (AAV)-based delivery of Cre recombinase with a mouse line amenable to Cre-based ablation of the Rspo2 exons encoding the receptor-binding domains. Such deletion of Rspo2 in the nodose-petrosal-jugular ganglion complex led to nearly complete loss of taste buds in the circumvallate papilla. Thus, we demonstrate that Rspo2 is the long-sought gustatory-neuron-supplied factor that acts on taste stem cells to maintain taste tissue homeostasis.

ACE1 knockout in neurons selectively dysregulates the hippocampal renin angiotensin system and causes vascular loss
Angiotensin I converting enzyme (ACE1) maintains blood pressure homeostasis by converting angiotensin I (angI) into angiotensin II (angII) in the renin-angiotensin system (RAS). ACE1 is expressed in the brain, where an intrinsic RAS regulates complex cognitive functions including learning and memory. ACE1 has been implicated in neurodegenerative disorders including Alzheimer's disease (AD) and Parkinson's disease (PD), but the mechanisms remain incompletely understood. Here, we performed single-nucleus RNA sequencing to characterize the expression RAS genes in the hippocampus and discovered that Ace is mostly expressed in CA region excitatory neurons. To gain a deeper understanding of the function of neuronal ACE1, we generated ACE1 conditional knockout (cKO) mice lacking ACE1 expression specifically in hippocampal and cortical excitatory neurons. Interestingly, ACE1 cKO mice exhibited hippocampus-dependent memory impairment in the Morris water maze, y-maze, and fear conditioning tests, but exhibited normal motor skills in rotarod. Total ACE1 level was significantly reduced in the cortex and hippocampus of ACE1 cKO mice showing that excitatory neurons are the predominant cell type expressing ACE1 in the forebrain. Despite similar reductions in total ACE1 level in both the hippocampus and cortex, the RAS pathway was dysregulated in the hippocampus only. Importantly, ACE cKO mice exhibited exacerbated age-related capillary loss selectively in the hippocampus. Here, we show selective vulnerability of the hippocampal microvasculature and RAS pathway to neuronal ACE1 knockout. Our results provide important insights into the function of ACE1 in the brain and demonstrate a connection between neuronal ACE and cerebrovascular function in the hippocampus.

Infant neural sensitivity to affective touch is associated with maternal postpartum depression
Classic attachment theory emphasizes the sensitivity of the parent to perceive and appropriately respond to the infant's cues. However, parent-child attachment is a dyadic interaction that is also dependent upon the sensitivity of the child to the early caregiving environment. Individual differences in infant sensitivity to parental cues is likely shaped by both the early caregiving environment as well as the infant's neurobiology, such as perceptual sensitivity to social stimuli. Here, we investigated associations between maternal postpartum depression and infant neurological sensitivity to affective touch using brain signal entropy - a metric of the brain's moment-to-moment variability related to signal processing. We recruited two independent samples of infants aged 0-5 months. In Sample 1 (n=67), we found increased levels of maternal postpartum depression were associated with diminished perceptual sensitivity - i.e. lower entropy - to affective tactile stimulation specifically within the primary somatosensory cortex. In Sample 2 (n=36), we replicated this finding and showed that this effect was not related to characteristics of the touch administered during the experiment. These results suggest that decreased affective touch early in life, a common consequence of postpartum depression, likely impacts the infant's perceptual sensitivity to affective touch and ultimately the experience-dependent neural networks that support the successful formation of attachment relationships.

Age-related dysregulation of the retinal transcriptome in African turquoise killifish
Age-related vision loss caused by neurodegenerative pathologies in the retina is becoming more prevalent in our ageing society. To understand the physiological and molecular impact of ageing on retinal homeostasis, we used the short-lived African turquoise killifish, a model known to naturally develop central nervous system (CNS) ageing hallmarks. Bulk and single-cell RNA-sequencing (scRNA-seq) of three age groups (6-, 12-, and 18-week-old) identified transcriptional ageing fingerprints in the killifish retina, unveiling pathways also identified in the aged brain, including oxidative stress, gliosis, and inflammageing. These findings were comparable to observations in ageing mouse retina. Additionally, transcriptional changes in genes related to retinal diseases, such as glaucoma and age-related macular degeneration, were observed. The cellular heterogeneity in the killifish retina was characterised, confirming the presence of all typical vertebrate retinal cell types. Data integration from age-matched samples between the bulk and scRNA-seq experiments revealed a loss of cellular specificity in gene expression upon ageing, suggesting potential disruption in transcriptional homeostasis. Differential expression analysis within the identified cell types highlighted the role of glial/immune cells as important stress regulators during ageing. Our work emphasises the value of the fast-ageing killifish in elucidating molecular signatures in age-associated retinal disease and vision decline. This study contributes to the understanding of how age-related changes in molecular pathways may impact CNS health, providing insights that may inform future therapeutic strategies for age-related pathologies.

Responses of neurons in macaque V4 to object and texture images
Humans and monkeys can effortlessly recognize objects in everyday scenes. This ability relies on neural computations in the ventral stream of visual cortex. The intermediate computations that lead to object selectivity are not well understood, but previous studies implicate V4 as an early site of selectivity for object shape. To explore the mechanisms of this selectivity, we generated a continuum of images between "scrambled" textures and photographic images of both natural and manmade environments, using techniques that preserve the local statistics of the original image while discarding information about scene and shape. We measured the responses of single units in awake macaque V4 to these images. On average, V4 neurons were slightly more active in response to photographic images than to their scrambled counterparts. However, responses in V4 varied widely both across different cells and different sets of images. An important determinant of this variation was the effectiveness of image families at driving strong neural responses. Across the full V4 population, a cell's average evoked firing rate for a family reliably predicted that family's preference for photographic over scrambled images. Accordingly, the cells that respond most strongly to each image family showed a much stronger difference between photographic and scrambled images and a graded level of modulation for images scrambled at intermediate levels. This preference for photographic images was not evident until ~50 ms after the onset of neuronal activity and did not peak in strength until 140 ms after activity onset. Finally, V4 neural responses seemed to categorically separate photographic images from all of their scrambled counterparts, despite the fact that the least scrambled images in our set appear similar to the originals. When these same images were analyzed with DISTS (Deep Image Structure and Texture Similarity), an image-computable similarity metric that predicts human judgements of image degradation, this same pattern emerged. This suggests that V4 responses are highly sensitive to small deviations from photographic image structure.

The Dorsal Column Nuclei Scales Mechanical Allodynia During Neuropathic Pain
Tactile perception relies on reliable transmission and modulation of low-threshold information as it travels from the periphery to the brain. During pathological conditions, tactile stimuli can aberrantly engage nociceptive pathways leading to the perception of touch as pain, known as mechanical allodynia. Two main drivers of peripheral tactile information, low-threshold mechanoreceptors (LTMRs) and postsynaptic dorsal column neurons (PSDCs), terminate in the brainstem dorsal column nuclei (DCN). Activity within the DRG, spinal cord, and DCN have all been implicated in mediating allodynia, yet the DCN remains understudied at the cellular, circuit, and functional levels compared to the other two. Here, we show that the gracile nucleus (Gr) of the DCN mediates tactile sensitivity for low-threshold stimuli and contributes to mechanical allodynia during neuropathic pain. We found that the Gr contains local inhibitory interneurons in addition to VPL-projecting neurons, which are differentially innervated by primary afferents and spinal inputs. Functional manipulations of these distinct Gr neuronal populations resulted in bidirectional changes to tactile sensitivity, but did not affect noxious mechanical or thermal sensitivity. During neuropathic pain, silencing Gr projection neurons or activating Gr inhibitory neurons was able to reduce tactile hypersensitivity, and enhancing inhibition was able to ameliorate paw withdrawal signatures of neuropathic pain, like shaking. Collectively, these results suggest that the Gr plays a specific role in mediating hypersensitivity to low-threshold, innocuous mechanical stimuli during neuropathic pain, and that Gr activity contributes to affective, pain-associated phenotypes of mechanical allodynia. Therefore, these brainstem circuits work in tandem with traditional spinal circuits underlying allodynia, resulting in enhanced signaling of tactile stimuli in the brain during neuropathic pain.

Monkeys engage in visual simulation to solve complex problems
Visual simulation - i.e., using internal reconstructions of the world to experience potential future versions of events that are not currently happening - is among the most sophisticated capacities of the human mind. But is this ability in fact uniquely human? To answer this question, we tested monkeys on a series of experiments involving the 'Planko' game, which we have previously used to evoke visual simulation in human participants. We found that monkeys were able to successfully play the game using a simulation strategy, predicting the trajectory of a ball through a field of planks while demonstrating a level of accuracy and behavioral signatures comparable to humans. Computational analyses further revealed that the monkeys' strategy while playing Planko aligned with a recurrent neural network (RNN) that approached the task using a spontaneously learned simulation strategy. Finally, we carried out awake functional magnetic resonance imaging while monkeys played Planko. We found activity in motion-sensitive regions of the monkey brain during hypothesized simulation periods, even without any perceived visual motion cues. This neural result closely mirrors previous findings from human research, suggesting a shared mechanism of visual simulation across species. In all, these findings challenge traditional views of animal cognition, proposing that nonhuman primates possess a complex cognitive landscape, capable of invoking imaginative and predictive mental experiences to solve complex everyday problems.

Contracted Functional Connectivity Profiles in Autism
Autism spectrum disorder (ASD) is a pervasive neurodevelopmental condition that is associated with atypical brain network organization, with prior work suggesting differential connectivity alterations with respect to functional connection length. Here, we tested whether functional connectopathy in ASD specifically relates to disruptions in long- relative to short-range functional connectivity profiles. Our approach combined functional connectomics with geodesic distance mapping, and we studied associations to macroscale networks, microarchitectural patterns, as well as socio-demographic and clinical phenotypes. We studied 211 males from three sites of the ABIDE-I dataset comprising 103 participants with an ASD diagnosis (mean (SD) age=20.8(8.1) years) and 108 neurotypical controls (NT, 19.2(7.2 years)). For each participant, we computed cortex-wide connectivity distance (CD) measures by combining geodesic distance mapping with resting-state functional connectivity profiling. We compared CD between ASD and NT participants using surface-based linear models, and studied associations with age, symptom severity, and intelligence scores. We contextualized CD alterations relative to canonical networks and explored spatial associations with functional and microstructural cortical gradients as well as cytoarchitectonic cortical types. Compared to NT, ASD participants presented with widespread reductions in CD, generally indicating shorter average connection length and thus suggesting reduced long-range connectivity but increased short-range connections. Peak reductions were localized in transmodal systems (i.e., heteromodal and paralimbic regions in the prefrontal, temporal, and parietal and temporo-parieto-occipital cortex), and effect sizes correlated with the sensory-transmodal gradient of brain function. ASD-related CD reductions appeared consistent across inter-individual differences in age and symptom severity, and we observed a positive correlation of CD to IQ scores. Our study showed reductions in CD as a relatively stable imaging phenotype of ASD that preferentially impacted paralimbic and heteromodal association systems. CD reductions in ASD corroborate previous reports of ASD-related imbalance between short-range overconnectivity and long-range underconnectivity.

Ephrin-B2 promotes nociceptive plasticity and hyperalgesic priming through EphB2-MNK-eIF4E signaling in both mice and humans
Ephrin-B-EphB signaling promotes pain through signaling between dorsal root ganglion (DRG) neurons and spinal cord neurons in the dorsal horn, and through signaling between peripheral cells and EphB receptors expressed by DRG neurons. Previous findings link ephrin-B expression in painful peripheral tissues in patients to chronic pain, suggesting the clinical significance of this signaling, but the direct effects of ephrins on DRG neurons have not been widely studied. We hypothesized that ephrin-B2 would promote nociceptor plasticity and hyperalgesic priming through MNK-eIF4E signaling, a critical mechanism for nociceptive plasticity induced by growth factors, cytokines and nerve injury. Our work demonstrates that ephrin-B2-EphB2 signaling drives activation of MNK-eIF4E in DRG neurons to cause an enhanced response to inflammatory mediator signaling in both mice and humans and hyperalgesic priming in two models in mice. Both male and female mice developed dose-dependent mechanical hypersensitivity in response to ephrin-B2, and both sexes showed hyperalgesic priming when challenged with PGE2 injection into the same hindpaw. Acute nociceptive behaviors and hyperalgesic priming were blocked in mice lacking MNK1 (Mknk1 knockout mice) and by the MNK inhibitor eFT508. Similar effects on hyperalgesic priming were seen in a dural injection model. We generated a sensory neuron specific knockout of EphB2 using Pirt-Cre mice and found that these mice lacked responses to ephrin-B2 injection. We used Ca2+-imaging to determine direct effects of ephrin-B2 on DRG neurons and found that ephrin-B2 treatment enhanced Ca2+ transients in response to PGE2 which were absent in DRG neurons from MNK1-/- and EphB2-PirtCre mice. In experiments on human DRG neurons we found that ephrin-B2 increased eIF4E phosphorylation and enhanced Ca2+ responses to PGE2 treatment, both of which were blocked by eFT508 treatment. We conclude that ephrin-B2 acts directly on mouse and human sensory neurons to induce nociceptor plasticity via MNK-eIF4E signaling. The findings offer insight into how ephrin-B signaling promotes pain, and suggests treatment avenues for prevention or reversal of chronic pain associated with EphB activation in sensory neurons.

Development of novel tools for dissection of central versus peripheral dopamine D2-like receptor signaling in dysglycemia
Dopamine (DA) D2-like receptors in both the central nervous system (CNS) and the periphery are key modulators of metabolism. Moreover, disruption of D2-like receptor signaling is implicated in dysglycemia. Yet, the respective metabolic contributions of CNS versus peripheral D2-like receptors including D2 (D2R) and D3 (D3R) receptors remain poorly understood. To address this, we developed new pharmacological tools, D2-like receptor agonists with diminished and delayed blood-brain barrier capability, to selectively manipulate D2R/D3R signaling in the periphery. We designated bromocriptine methiodide (BrMeI), a quaternary methiodide analogue of D2/3R agonist and diabetes drug bromocriptine, as our lead compound based on preservation of D2R/D3R binding and functional efficacy. We then used BrMeI and unmodified bromocriptine to dissect relative contributions of CNS versus peripheral D2R/D3R signaling in treating dysglycemia. Systemic administration of bromocriptine, with unrestricted access to CNS and peripheral targets, significantly improved both insulin sensitivity and glucose tolerance in obese, dysglycemic mice in vivo. In contrast, metabolic improvements were attenuated when access to bromocriptine was restricted either to the CNS through intracerebroventricular administration or delayed access to the CNS via BrMeI. Our findings demonstrate that the coordinated actions of both CNS and peripheral D2-like receptors are required for correcting dysglycemia. Ultimately, the development of a first-generation of drugs designed to selectively target the periphery provides a blueprint for dissecting mechanisms of central versus peripheral DA signaling and paves the way for novel strategies to treat dysglycemia.

Improved BOLD Detection with Sliced Inverse Regression
Functional magnetic resonance imaging (fMRI) has been effective in linking task-related brain responses to changes in blood oxygen level density (BOLD). However, its reliance on BOLD measurements makes it vulnerable to artifacts and false-positive signals. Commonly, researchers use many regressors in a General Linear Model to filter true signals, but this adds noise and complicates interpretation. In this paper we suggest using Sliced Inverse Regression (SIR) to simplify covariate dimensionality and identify relevant regressors. We compare a general linear model applied to both original and SIR-adjusted data, demonstrating that SIR improves signal detection, reduces noise, and yields statistically significant results even with conservative measures.

Transient DREADD manipulation of the dorsal Dentate Gyrus in rats impairs disambiguation of similar place-outcome associations
The dentate gyrus subfield of the hippocampus is thought to be critically involved in the disambiguation of similar episodic experiences and places in a context-dependent manner. However, most empirical evidence has come from lesion and gene knock-out studies in rodents, in which the dentate gyrus function is permanently perturbed and compensation of affected functions via other areas within the memory circuit could take place. The acute and causal role of the dentate gyrus herein remains therefore elusive. The present study aimed to investigate the acute role of the dorsal dentate gyrus in disambiguation learning using reversible inhibitory DREADDs. Rats were trained on a location discrimination task and learnt to discriminate between a rewarded and unrewarded location with either small (similar condition) or large (dissimilar condition) separation. Reward contingencies switched after a reversal rule, allowing us to track the temporal engagement of the dentate gyrus during the task. Bilateral but not unilateral DREADD modulation of the dentate gyrus impaired the initial acquisition learning of place-reward associations, but performance rapidly recovered to control levels within the same session. Modelling of the behavioural patterns revealed that reward learning and reward sensitivity were not associated with the DREADD-dependent impairment during acquisition learning, suggesting that either the ability to encode place-reward associations, or the fine-grained coding of place were instead affected. Our study thus provides novel evidence that the dorsal dentate gyrus is acutely and bilaterally engaged during the initial acquisition learning of ambiguous place-reward associations, although the exact neural mechanisms supporting this function still need to be fully understood.

Probabilistic Inference on Virtual Brain Models of Disorders
Connectome-based models, also known as Virtual Brain Models (VBMs), have been well established in network neuroscience to investigate pathophysiological causes underlying a large range of brain diseases. The integration of an individual's brain imaging data in VBMs has improved patient-specific predictivity, although Bayesian estimation of spatially distributed parameters remains challenging even with state-of-the-art Monte Carlo sampling. VBMs imply latent nonlinear state space models driven by noise and network input, necessitating advanced probabilistic machine learning techniques for widely applicable Bayesian estimation. Here we present Simulation-Based Inference on Virtual Brain Models (SBI-VBMs), and demonstrate that training deep neural networks on both spatio-temporal and functional features allows for accurate estimation of generative parameters in brain disorders. The systematic use of brain stimulation provides an effective remedy for the non-identifiability issue in estimating the degradation of intra-hemispheric connections. By prioritizing model structure over data, we show that the hierarchical structure in SBI-VBMs renders the inference more effective, precise and biologically plausible. This approach could broadly advance precision medicine by enabling fast and reliable prediction of patient-specific brain disorders.

Spatial context non-uniformly modulates inter-laminar communication in the primary visual cortex
Our visual experience is a result of the concerted activity of neuronal ensembles in the sensory hierarchy. Yet how the spatial organization of objects influences neural activity in this hierarchy remains poorly understood. We investigate how the inter-laminar interactions in the primary visual cortex (V1) are affected by visual stimuli in isolation or with flanking stimuli at various spatial configurations that are known to cause non-uniform degradation of perception. By employing dimensionality reduction approaches to simultaneous layer-specific population recordings, we establish that cortical layers interact through a structurally stable communication subspace. Spatial configuration of contextual stimuli differentially modulates inter-laminar communication efficacy, the balance between feedforward and feedback signaling, and contextual signaling in the superficial layers. Remarkably, these modulations mirror the spatially non-uniform aspects of perceptual degradation. Our results suggest a model of retinotopically non-uniform cortical connectivity in the output layers of V1 that influences communication in the sensory hierarchy.

A site-wise reliability analysis of the ABCD diffusion fractional anisotropy data, impact of the scanner and analytical pipeline
The Adolescent Brain and Cognitive Development (ABCD) project is the largest longitudinal study of brain development that tracts 11,820 subjects from 21 sites using standardized protocols for multi-site data collection and analysis. Adolescence is a critical period of brain development associated with white matter myelination and requires reliable measures to detect these changes. We assessed confounding non-biological variances in diffusion tensor imaging (DTI) data that may be present due to technological variations, participant compliance and data analysis protocols. ABCD imaging data were collected biannually, and thus ongoing maturation may artificially introduce bias to classical test-retest approaches such as the interclass correlation coefficients (ICC). To address this, we developed a site-wise adaptive ICC (AICC) to systematically evaluate the quality of imaging-derived phenotypes while accounting for ongoing brain development. We measured the age-related brain development trajectory and estimated site-wise AICC iteratively, adjusting the weight for each site based on the ICC scores. We evaluated longitudinal reliability of diffusion fractional anisotropy (FA) data for each site, considering the impact of MRI scanner platform and standard ABCD versus ENIGMA-DTI data extraction pipelines, and comparing longitudinal stability of FA measurements to these of the cortical thickness. The ENIGMA structural and diffusion pipeline with QA/QC improved the average reliability for cortical FA to AICC=0.70{+/-}0.19, compared to 0.61{+/-}0.19 for the standard ABCD pipeline (Wilcoxon test p<0.001). Furthermore, we showed that the AICC for sites that used Siemens scanners significantly outperformed those using GE/Phillips scanners (AICC=0.78{+/-}0.11 vs 0.62{+/-}0.21, p<0.001). In conclusion, variations in data quality among study sites and preprocessing pipelines underscore the necessity for meticulous data curation in subsequent association analyses.

HippoMaps: Multiscale cartography of the human hippocampal formation
AO_SCPLOWBSTRACTC_SCPLOWThe hippocampus has a unique microarchitecture, is situated at the nexus of multiple macroscale functional networks, contributes to numerous cognitive as well as affective processes, and is highly susceptible to brain pathology across common disorders. These features make the hippocampus a model to understand how brain structure covaries with function, in both health and disease. Here, we introduce HippoMaps, an open access toolbox and online data warehouse for the mapping and contextualization of hippocampal data in the human brain (http://hippomaps.readthedocs.io). HippoMaps capitalizes on a novel hippocampal unfolding approach as well as shape intrinsic registration capabilities to allow for cross-subject and cross-modal data aggregation. We initialize this repository with data spanning 3D post-mortem histology, ex-vivo 9.4 Tesla MRI, as well as in-vivo structural MRI and resting-state functional MRI (rsfMRI) obtained at 3 and 7 Tesla, together with intracranial encephalography (iEEG) recordings in epilepsy patients. HippoMaps also contains validated tools for spatial map association analysis in the hippocampus that correct for autocorrelation. All code and data are compliant with community standards, and comprehensive online tutorials facilitate broad adoption. Applications of this work span methodologies and modalities, spatial scales, as well as clinical and basic research contexts, and we encourage community feedback and contributions in the spirit of open and iterative scientific resource development.

Investigating the ability of music to induce calm in young adults.
Music medicine may allow individuals with sub-clinical anxiety levels to self-medicate when and where they choose. The current study used subjective and objective anxiety measures to compare musics ability to change emotional states. Subjective measures included ratings of a songs pleasantness, arousal, dominance, and likability, as well as state and trait anxiety estimates. Objective measures were selected for skin conductance, heart rate (HR), and blood volume pulse (BVP) amplitude. The commercially available music consisted of ambient, metal, and pop songs. The participants, 28 young adults, listened to the six songs. During the songs, objective measurements were obtained, rating the songs affective dimensions as they listened and their state of anxiety after each song. Results support the notion that different music genres can differentially affect subjective and objective measures of negative emotion. Specifically, low arousal / high valance songs were associated with lower state anxiety and physiological arousal levels. Discussion around the promise of music medicine and aspects of its management are presented, along with avenues of further inquiry.

Memory load influences our preparedness to act on visual representations in working memory without affecting their accessibility
It is well established that when we hold more content in working memory, we are slower to act upon specific content when it becomes relevant for behavior. Here, we asked whether slower responses with higher working-memory load can be accounted for by slower access to sensory representations held in working memory (according to a serial internal search), or by a lower preparedness to act upon them. To address this, we designed a visual-motor working-memory task in which participants memorized the orientation of two or four colored bars, of which one was cued for reproduction. We independently tracked the selection of visual (cued item location) and motor (relevant manual action) information from the EEG time-frequency signal, and compared their latencies between our memory-load conditions. We confirm slower memory-guided behavior with higher working-memory load and show that this is associated with delayed motor selection, but find no evidence for a concomitant delay in the latency of visual selection. Moreover, we show that variability in decision times within each memory-load condition is associated with corresponding changes in the latency of motor, but not visual selection. These results reveal how memory load affects our preparedness to act on, without necessarily changing the ability to access, sensory representations in working memory. This posits action readiness is a key factor that shapes the speed of memory-guided behavior and that underlies delayed responses with higher working-memory load.

Spiral ganglion neuron degeneration in deafened rats involves innate and adaptive immune responses not requiring complement
Spiral ganglion neurons (SGNs) transmit auditory information from cochlear hair cells to the brain. SGNs are thus not only important for normal hearing, but also for effective functioning of cochlear implants, which stimulate SGNs when hair cells are missing. SGNs slowly degenerate following aminoglycoside-induced hair cell loss, a process thought to involve an immune response. However, the specific immune response pathways involved remain unknown. We used RNAseq to gain a deeper understanding immune-related and other transcriptomic changes that occur in the rat spiral ganglion after kanamycin-induced deafening. Among the immune and inflammatory genes that were selectively upregulated in deafened spiral ganglia, the complement cascade genes were prominent. We then assessed SGN survival, as well as immune cell infiltration and activation, in the spiral ganglia of rats with a CRISPR-Cas9-mediated knockout of complement component 3 (C3). Similar to previous findings in our lab and other deafened rodent models, we observed infiltration of macrophages and increased expression of CD68, a marker of phagocytic activity and cell activation, in the deafened ganglia. Moreover, we found that the immune response also includes MHCII+ macrophages and CD45+ and lymphocytes, indicative of an adaptive response. However, C3 knockout did affect SGN survival or macrophage infiltration/activation, indicating that complement activation does not play a role in SGN death after deafening. Together, these data suggest that both innate and adaptive immune responses are activated in the deafened spiral ganglion, with the adaptive response directly contributing to cochlear neurodegeneration.

A multi-symptomatic model of heroin use disorder in rats reveals distinct behavioral profiles and neuronal correlates of heroin vulnerability versus resiliency
ObjectiveThe behavioral and diagnostic heterogeneity within human opioid use disorder (OUD) diagnosis is not readily captured in current animal models, limiting translational relevance of the mechanistic research that is conducted in experimental animals. We hypothesize that a non-linear clustering of OUD-like behavioral traits will capture population heterogeneity and yield subpopulations of OUD vulnerable rats with distinct behavioral and neurocircuit profiles.

MethodsOver 900 male and female heterogeneous stock rats, a line capturing genetic and behavioral heterogeneity present in humans, were assessed for several measures of heroin use and rewarded and non-rewarded seeking behaviors. Using a non-linear stochastic block model clustering analysis, rats were assigned to OUD vulnerable, intermediate and resilient clusters. Additional behavioral tests and circuit analyses using c-fos activation were conducted on the vulnerable and resilient subpopulations.

ResultsOUD vulnerable rats exhibited greater heroin taking and seeking behaviors relative to those in the intermediate and resilient clusters. Akin to human OUD diagnosis, further vulnerable rat sub- clustering revealed subpopulations with different combinations of behavioral traits, including sex differences. Lastly, heroin cue-induced neuronal patterns of circuit activation differed between resilient and vulnerable phenotypes. Behavioral sex differences were recapitulated in patterns of circuitry activation, including males preferentially engaging extended amygdala stress circuitry, and females cortico-striatal drug cue-seeking circuitry.

ConclusionUsing a non-linear clustering approach in rats, we captured behavioral diagnostic heterogeneity reflective of human OUD diagnosis. OUD vulnerability and resiliency were associated with distinct neuronal activation patterns, posing this approach as a translational tool in assessing neurobiological mechanisms underpinning OUD.

Investigating the effects of repetitive paired-pulse transcranial magnetic stimulation on visuomotor training using TMS-EEG.
ObjectivesI-wave periodicity repetitive paired-pulse transcranial magnetic stimulation (iTMS) can modify acquisition of a novel motor skill, but the associated neurophysiological effects remain unclear. The current study therefore used combined TMS-electroencephalography (TMS-EEG) to investigate the neurophysiological effects of iTMS on subsequent visuomotor training (VT).

MethodsSixteen young adults (26.1 {+/-} 5.1 years) participated in three sessions including real iTMS and VT (iTMS + VT), control iTMS and VT (iTMSsham + VT), or iTMS alone. Motor-evoked potentials (MEPs) and TMS-evoked potentials (TEPs) were measured before and after iTMS, and again after VT, to assess neuroplastic changes.

ResultsIrrespective of the intervention, MEP amplitude was not changed after iTMS or VT (P = 0.211). Motor skill was improved compared with baseline (P < 0.001), but no differences were found between stimulus conditions. In contrast, the P30 peak was altered by VT when preceded by sham iTMS (P < 0.05), but this effect was not apparent when VT was preceded by iTMS or following iTMS alone (all P > 0.15).

ConclusionIn contrast to expectations, iTMS was unable to modulate MEP amplitude or influence motor learning. Despite this, changes in P30 amplitude suggested that motor learning was associated with altered cortical reactivity. Furthermore, this effect was abolished by priming with iTMS, suggesting an influence of priming that failed to impact learning.

Authorship statementsConceptualization: JGS; Data curation: RS, BJH, and WL; Formal analysis: RS; Funding acquisition: RS; Investigation: RS, BJH, and WL; Methodology: RS, GMO, BJH and JGS; Project administration: GMO and JGS; Supervision: GMO and JGS; Roles/Writing - original draft: RS and GMO; Writing - review & editing: BJH, WL, and JGS.

ErbB inhibition rescues nigral dopamine neuron hyperactivity and repetitive behaviors in a mouse model of fragile X syndrome
Repetitive behaviors are core symptoms of autism spectrum disorders (ASD) and fragile X syndrome (FXS), the prevalent genetic cause of intellectual disability and autism. The nigrostriatal dopamine (DA) circuit rules movement and habit formation; therefore, its dysregulation stands as a leading substrate for repetitive behaviors. However, beyond indirect evidence, specific assessment of nigral DA neuron activity in ASD and FXS models is lacking. Here, we show that hyperactivity of substantia nigra pars compacta (SNpc) DA neurons is an early feature of FXS. The underlying mechanisms rely on mGluR1 and ErbB receptors. Up-regulation of ErbB4 and ErbB2 in nigral DA neurons drives neuronal hyperactivity and repetitive behaviors of the FXS mouse, simultaneously rescued by ErbB inhibition. In conclusion, beyond providing the first evidence of dysregulation of the SNpc DA nucleus in FXS, we identify novel targets - ErbB receptors - whose inhibition proficiently attenuates repetitive behaviors, thus opening an avenue toward innovative therapies for ASD and FXS.

Emergence of a synergistic scaffold in the brains of human infants
The human brain is a complex organ comprising billions of interconnected neurons which enables interaction with both physical and social environments. Neural dynamics of the whole brain go far beyond just the sum of its individual elements; a property known as "synergy". Previously it has been shown that synergy is crucial for many complex brain functions and cognition, however, it remains unknown how and when the large number of discrete neurons evolve into the unified system able to support synergistic interactions. Here we analysed high-density electroencephalography data from late fetal to early postnatal period. We found that the human brain transitions from redundancy-dominated to synergy-dominated system around birth. Frontal regions lead the emergence of a synergistic scaffold comprised of overlapping subsystems, while the integration of sensory areas developed gradually, from occipital to central regions. Strikingly, early developmental trajectories of brain synergy were modulated by environmental enrichment associated with enhanced mother-infant interactions, and the level of synergy near term equivalent age was associated with later neurocognitive development.

Knockout of AMPA receptor binding protein Neuron-Specific Gene 2 (NSG2) enhances associative learning and cognitive flexibility
The vast majority of gene mutations and/or gene knockouts result in either no observable changes, or significant deficits in molecular, cellular, or organismal function. However, in a small number of cases, mutant animal models display enhancements in specific behaviors such as learning and memory. To date, most gene deletions shown to enhance cognitive ability generally affect a limited number of pathways such as NMDA receptor- and translation-dependent plasticity, or GABA receptor- and potassium channel-mediated inhibition. While endolysosomal trafficking of AMPA receptors is a critical mediator of synaptic plasticity, mutations in genes that affect AMPAR trafficking either have no effect or are deleterious for synaptic plasticity, learning and memory. NSG2 is one of the three-member family of Neuron-specific genes (NSG1-3), which have been shown to regulate endolysosomal trafficking of a number of proteins critical for neuronal function, including AMPAR subunits (GluA1-2). Based on these findings and the largely universal expression throughout mammalian brain, we predicted that genetic knockout of NSG2 would result in significant impairments across multiple behavioral modalities including motor, affective, and learning/memory paradigms. However, in the current study we show that loss of NSG2 had highly selective effects on associative learning and memory, leaving motor and affective behaviors intact. For instance, NSG2 KO animals performed equivalent to wild-type C57Bl/6n mice on rotarod and Catwalk motor tasks, and did not display alterations in anxiety-like behavior on open field and elevated zero maze tasks. However, NSG2 KO animals demonstrated enhanced recall in the Morris water maze, accelerated reversal learning in a touch-screen task, and accelerated acquisition and recall on a Trace Fear Conditioning task. Together, these data point to a specific involvement of NSG2 on multiple types of associative learning, and expand the repertoire of pathways that can be targeted for cognitive enhancement.

Activity-dependent regulation of vascular cholesterol metabolism acts as a negative feedback mechanism for neurovascular coupling
Brain function is dependent on a continuous supply of bloodborne oxygen and nutrients. Because neurons require a greater supply of oxygen and nutrients when active, there is increased local blood flow following neuronal activity. The underlying mechanisms of this hyperemia are termed neurovascular coupling (NVC). Many complex processes contribute to NVC, and there is still much unknown about how vascular physiology adapts to changes in neuronal activity and blood flow. Here we show that neuronal activity increases brain endothelial expression of genes related to cholesterol synthesis and uptake in vivo, and that shear stress is sufficient for upregulation of these genes in vitro. We previously found that treatment with PLX5622 induces upregulation of the same cassette of cholesterol-related genes in brain endothelial cells. In the present study, we find that increasing brain endothelial cholesterol synthesis and/or uptake, either with PLX5622 or targeted AAV-mediated expression of LDLR, inhibits brain arteriole dilation in response to capillary K+ stimulation, and this deficit is rescued by cholesterol depletion. Together, these data suggest that neuronal activity regulates brain endothelial cholesterol, which in turn blocks endothelial retrograde signaling and vasodilation, thus acting as a negative feedback mechanism for NVC.