bioRxiv Subject Collection: Neuroscience's Journal

Inverse and Postponed Impacts of Extracellular Tau PHF on Astrocytes and Neurons' Mitochondrial Function
Background: Tauopathies encompass a spectrum of neurodegenerative disorders which are marked by the pathological aggregation of tau protein into paired helical filaments (PHF-tau), neurofibrillary tangles (NFTs) and Glial-fibrillary tangles (GFTs). These aggregates impair cellular, mitochondrial, and synaptic functions. The emergence of extracellular tau (ePHF-tau), featuring a myriad of isoforms and phosphorylation states, presents a challenge in comprehending its nuanced effects on neural cells, particularly concerning synaptic and mitochondrial integrity. Methods: We studied the impact of ePHF-tau (2N4R) on different states and ages of primary cultures of rat neuroglia. Using confocal microscopy and proteomic analysis of synaptosomes, we studied the impact of ePHF-tau on neurite and synapse number. We monitored mitochondrial responses in neurons and astrocytes over 72 hours using advanced fluorescence microscopy for dynamic, high-throughput analysis. Results: Treatment with ePHF-tau has a strong effect on the neurites of immature neurons, but its toxicity is negligible when the neurons are more mature. At the mature stage of their development, we observed a substantial increase in the density of the PSD-95/vGlut1 zone in neurite, suggesting altered synaptic connectivity and ePHF-tau excitotoxicity. Proteomics revealed significant changes in mitochondrial protein in synaptosomes following exposure to ePHF-tau. In the neuronal compartment, real-time imaging revealed rapid and persistent mitochondrial dysfunction, increased ATP production, and reduced mitochondrial turnover. In contrast, we observed increased mitochondrial turnover and filamentation after treatment in the astrocyte processes, indicating cell-specific adaptive responses to ePHF-tau. Conclusions: This study sheds light on the intricate effects of extracellular tau aggregates on neuronal and astrocytic mitochondrial populations, highlighting how tau pathology can lead to mitochondrial disturbances and synaptic alterations. By delineating the differential responses of neurons and astrocytes to ePHF-tau, our findings pave the way for developing targeted therapeutic interventions to mitigate the detrimental impacts of tau aggregates in neurodegenerative diseases.

Parallel Encoding of Speech in Human Frontal and Temporal Lobes
Models of speech perception are centered around a hierarchy in which auditory representations in the thalamus propagate to primary auditory cortex, then to the lateral temporal cortex, and finally through dorsal and ventral pathways to sites in the frontal lobe. However, evidence for short latency speech responses and low-level spectrotemporal representations in frontal cortex raises the question of whether speech-evoked activity in frontal cortex strictly reflects downstream processing from lateral temporal cortex or whether there are direct parallel pathways from the thalamus or primary auditory cortex to the frontal lobe that supplement the traditional hierarchical architecture. Here, we used high-density direct cortical recordings, high-resolution diffusion tractography, and hemodynamic functional connectivity to evaluate for evidence of direct parallel inputs to frontal cortex from low-level areas. We found that neural populations in the frontal lobe show speech-evoked responses that are synchronous or occur earlier than responses in the lateral temporal cortex. These short latency frontal lobe neural populations encode spectrotemporal speech content indistinguishable from spectrotemporal encoding patterns observed in the lateral temporal lobe, suggesting parallel auditory speech representations reaching temporal and frontal cortex simultaneously. This is further supported by white matter tractography and functional connectivity patterns that connect the auditory nucleus of the thalamus (medial geniculate body) and the primary auditory cortex to the frontal lobe. Together, these results support the existence of a robust pathway of parallel inputs from low-level auditory areas to frontal lobe targets and illustrate long-range parallel architecture that works alongside the classical hierarchical speech network model.

Impact of analytic decisions on test-retest reliability of individual and group estimates in functional magnetic resonance imaging: a multiverse analysis using the monetary incentive delay task
Empirical studies reporting low test-retest reliability of individual blood oxygen-level dependent (BOLD) signal estimates in functional magnetic resonance imaging (fMRI) data have resurrected interest among cognitive neuroscientists in methods that may improve reliability in fMRI. Over the last decade, several individual studies have reported that modeling decisions, such as smoothing, motion correction and contrast selection, may improve estimates of test-retest reliability of BOLD signal estimates. However, it remains an empirical question whether certain analytic decisions consistently improve individual and group level reliability estimates in an fMRI task across multiple large, independent samples. This study used three independent samples (Ns: 60, 81, 120) that collected the same task (Monetary Incentive Delay task) across two runs and two sessions to evaluate the effects of analytic decisions on the individual (intraclass correlation coefficient [ICC(3,1)]) and group (Jaccard/Spearman rho) reliability estimates of BOLD activity of task fMRI data. The analytic decisions in this study vary across four categories: smoothing kernel (five options), motion correction (four options), task parameterizing (three options) and task contrasts (four options), totaling 240 different pipeline permutations. Across all 240 pipelines, the median ICC estimates are consistently low, with a maximum median ICC estimate of .44 - .55 across the three samples. The analytic decisions with the greatest impact on the median ICC and group similarity estimates are the Implicit Baseline contrast, Cue Model parameterization and a larger smoothing kernel. Using an Implicit Baseline in a contrast condition meaningfully increased group similarity and ICC estimates as compared to using the Neutral cue. This effect was largest for the Cue Model parameterization, however, improvements in reliability came at the cost of interpretability. This study illustrates that estimates of reliability in the MID task are consistently low and variable at small samples, and a higher test-retest reliability may not always improve interpretability of the estimated BOLD signal.

Otoferlin requires a free intravesicular C-terminal end for synaptic vesicle docking and fusion
Our understanding of how otoferlin, the major calcium sensor in inner hair cells (IHCs) synaptic transmission, contributes to the overall dynamics of synaptic vesicle (SV) trafficking remains limited. To address this, we generated a knock-in mouse model expressing an otoferlin-GFP protein, where GFP was fused to its C-terminal transmembrane domain. Similar to the wild type protein, the GFP-tagged otoferlin showed normal expression and was associated with IHC SV. Surprisingly, while the heterozygote Otof+/GFP mice exhibited a normal hearing function, homozygote OtofGFP/GFP mice were profoundly deaf attributed to severe reduction in SV exocytosis. Fluorescence recovery after photobleaching revealed a markedly increased mobile fraction of the otof-GFP-associated SV in OtofGFP/GFP IHCs. Correspondingly, 3D-electron tomographic of the ribbon synapses indicated a reduced density of SV attached to the ribbon active zone. Collectively, these results indicate that otoferlin requires a free intravesicular C-terminal end for normal SV docking and fusion.

Eye-movement artifact correction in infant EEG
Background Independent Component Analysis (ICA) is a well-established approach to clean EEG and remove the impact of signals of non-neural origin, such as those from muscular activity and eye movements. However, evidence suggests that ICA removes artifacts less effectively in infants than in adults. This study systematically compares ICA and Artifact Blocking (AB), an alternative approach proposed to improve eye-movement artifact correction in infant EEG. Methods We analyzed EEG collected from 50 infants between 6 and 18 months of age as part of the International Infant EEG Data Integration Platform (EEGIP), a longitudinal multi-study dataset. EEG was recorded while infants sat on their caregivers laps and watched videos. We used ICA and AB to correct for eye-movement artifacts in the EEG and calculated the proportion of effectively corrected segments, signal-to-noise ratio (SNR), power-spectral density (PSD), and multiscale entropy (MSE) in manually selected segments with and without eye-movement artifacts. Results On the one hand, the proportion of effectively corrected segments indicated that ICA corrected eye-movement artifacts (sensitivity) better than AB. SNR and PSD indicated that both AB and ICA correct eye-movement artifacts with equal sensitivity. MSE gave mixed results. On the other hand, AB caused less distortion to the clean segments (specificity) for SNR, PSD, and MSE. Conclusions Our results suggest that ICA is more sensitive (i.e., it better removes artifacts) but less specific (it distorts clean signals) than AB for correcting eye-movement artifacts in infant EEG.

When spatial attention cannot be divided: Quadrantic enhancement of early visual processing across task-relevant and irrelevant locations
Spatial attention enables us to select regions of space and prioritize visual processing at the attended locations. Previous research has shown that spatial attention can be flexibly tuned to broader or narrower regions in space, and in some cases be split amongst multiple locations. Here, we investigate how attentional resources are distributed within a visual quadrant when participants are instructed to either focus attention narrowly, broadly, or split attention among two non-contiguous locations. Using a combination of behavior and steady-state visual-evoked potentials (SSVEP), the oscillatory response of the visual cortex to incoming flickering stimuli, we find clear evidence for ineffective splitting of spatial attention within a visual quadrant. Importantly, by assessing visual-cortical processing across locations at a high spatial resolution (by flickering nearby locations at distinct frequencies), our results reveal that attention was distributed in the exact same manner regardless of whether participants were instructed to attend broadly across a large region of space, or divide attention amongst two non-contiguous locations: In both cases, the intermediate location showed the strongest boost in visual-cortical processing, no matter whether it was the center of the attended region (broad-focus condition), or the uncued, to-be-ignored location (split-focus condition). Thus, the present study provides strong evidence that when trying to attend to multiple separate locations within a visual quadrant, sustained attention inadvertently enhances visual processing at the intermediate location even when it is detrimental to task performance.

Assistive sensory-motor perturbations influence learned neural representations
Task errors are used to learn and refine motor skills. We investigated how task assistance influences learned neural representations using Brain-Computer Interfaces (BCIs), which map neural activity into movement via a decoder. We analyzed motor cortex activity as monkeys practiced BCI with a decoder that adapted to improve or maintain performance over days. Population dimensionality remained constant or increased with learning, counter to trends with non-adaptive BCIs. Yet, over time, task information was contained in a smaller subset of neurons or population modes. Moreover, task information was ultimately stored in neural modes that occupied a small fraction of the population variance. An artificial neural network model suggests the adaptive decoders contribute to forming these compact neural representations. Our findings show that assistive decoders manipulate error information used for long-term learning computations, like credit assignment, which informs our understanding of motor learning and has implications for designing real-world BCIs.

Deciphering the Role of Aggrecan in Parvalbumin Interneurons: Unexpected Outcomes from a Conditional ACAN Knockout That Eliminates WFA+ Perineuronal Nets
The transition from juvenile to adult is accompanied by the maturation of inhibitory parvalbumin-positive (PV+) neurons and reduced plasticity. This transition involves the formation of perineuronal nets (PNNs), a dense configuration of the extracellular matrix that predominantly envelops parvalbumin-positive (PV+) neurons. Aggrecan, a proteoglycan encoded by the ACAN gene, has been shown to have a key role in the PNNs as knock-out of ACAN in the adult brain reactivates juvenile plasticity, but the contribution of different cell populations is unknown

Here, we establish and characterize a mouse model in which ACAN is selectively knocked out (KO) in PV+ neurons (ACANflx/PVcre). Moreover, we develop a viral tool to perform similar cell-type directed KO in adult mice. Both models are compared with the traditional method of PNN removal, namely enzymatic degradation of PNNs with Chondroitinase ABC (chABC).

We show that PV+ neurons in adult ACANflx/PVcre mice do not produce PNNs that are labeled by Wisteria floribunda agglutinin (WFA), the most commonly used PNN marker. Surprisingly, electrophysiological properties of PV+ interneurons in the visual cortex (V1) and ocular dominance plasticity of adult ACANflx/PVcre mice were similar to controls. In contrast, AAV-mediated ACAN knockout in adult mice increased ocular dominance plasticity. Moreover, in vivo chABC treatment of KO mice resulted in reduced firing rate of PV+ cells and increased frequency of spontaneous excitatory postsynaptic currents (sEPSC), a phenotype associated with chABC treatment of WT animals. This suggests compensatory mechanisms in the germline KO. Indeed, qPCR of bulk tissue indicates that other PNN components are expressed at higher levels in the KO animals. Finally, we perform memory-and behavioral testing to see if the lack of ACAN from PV+ neurons throughout development affected stereotypic behaviors and memory processing. ACANflx/PVcre mice have learning and memory abilities similar to controls, but use bold search strategies during navigation in the Morris water maze. The low level of anxiety-related behavior is confirmed in an open field and zero maze, where they spent nearly twice the time in open areas.

Sub-clinical glutamate receptor antagonist combinations prevent progressive demyelination.
Multiple sclerosis (MS) affects almost 3 million people globally who suffer demyelination as a series of relapses and remissions that tend towards progressive deterioration over time. The proximate cause is auto-immune attack by the adaptive immune system; therapies directed against this are effective during the relapsing-remitting phase but are less effective or ineffective during progression where other injury mechanisms may be significant. LPS- and cuprizone-induced experimental demyelination share features of progressive demyelination in MS but the underlying mechanisms are not well understood. We show here that these demyelination models can be reproduced ex vivo using short protocols, revealing that combined antagonism of two types of glutamate receptor, NMDA and AMPA, using clinically approved antagonists at sub-clinical doses, can protect against these forms of demyelination. Combined low dose therapy was subsequently shown to be effective in vivo against dietary cuprizone and experimental autoimmune-encephalomyelitis (EAE) models of demyelination and, in particular, protected the smaller myelinated axons that are the main substrate of the function loss in progressive MS.

Theta transcranial alternating current stimulation is not effective in improving working memory performance
Extensive research has established a significant relationship between frontal midline theta (FMT) activity in the 4-8 Hz range and working memory (WM) performance. Transcranial alternating current stimulation (tACS) is recognized for inducing lasting changes in brain oscillatory activity. Across two experiments, we tested the possibility that WM could be improved through tACS stimulation of dorsomedial prefrontal cortex (dmPFC) and anterior cingulate cortex (ACC), by affecting executive control networks associated with FMT. In Experiment 1, following either a 20-minute verum or sham stimulation applied to Fpz-CPz at 1 mA and 6 Hz, 31 participants performed WM tasks, while EEG was recorded. The task required participants to either mentally manipulate memory items or retain them in memory as they were originally presented. No significant effects were observed in behavioral performance, and we found no change in theta activity during rest and task following stimulation. However, alpha activity during retention or manipulation of information in WM was less strongly enhanced following verum stimulation as compared with sham. In Experiment 2 (N = 25), tACS was administered during and after the task in two separate sessions. Here, we changed the order of the stimulation blocks: a 25-minute task block was either accompanied first by sham stimulation and then by verum stimulation, or vice versa. Taken together, our results show no improvements in WM performance through tACS after-effects or online stimulation and demonstrate that theta frequency tACS applied at the midline is not an effective method for enhancing WM performance.

Variations in clustering of multielectrode local field potentials in the motor cortex of macaque monkeys during a reach-and-grasp task
There is experimental evidence of varying correlation among the elements of the neuromuscular system over the course of the reach-and-grasp task. Several neuromuscular disorders are accompanied by anomalies in muscular coupling during the task. The aim of this study was to investigate if modifications in correlations and clustering can be detected in the Local Field Potential (LFP) recordings of the motor cortex during the task. To this end, we analyzed the LFP recordings from a previously published study on monkeys which performed a reach-and-grasp task for targets with a vertical or horizontal orientation. LFP signals were recorded from the motor and premotor cortex of macaque monkeys as they performed the task. We found very robust changes in the correlations of the multielectrode LFP recordings which corresponded to task epochs. Mean LFP correlation increased significantly during reaching and then decreased during grasp. This pattern was very robust for both left and right arm reaches irrespective of target orientation. A hierarchical cluster analysis supported the same conclusion - a decreased number of clusters during reach followed by an increase for grasp. A sliding window computation of the number of clusters was performed to probe the predictive capacities of these LFP clusters for upcoming task events. For a very high percentage of trials (95.3%), there was a downturn in cluster number following the Pellet Drop (GO signal) which reached a minimum shortly preceding the Start of grasp, hence indicating that cluster analyses of LFP signals could provide online indications of the Start of grasp.

Biphasic Internetwork Coordination is Funneled through an Electrical Synapse
Linked rhythmic behaviors, such as respiration/locomotion or swallowing/chewing often require coordination for proper function. Despite its prevalence, the cellular mechanisms controlling coordination of the underlying neural networks remain undetermined in most systems. We use the stomatogastric nervous system of the crab Cancer borealis to investigate mechanisms of internetwork coordination, due to its small, well characterized feeding-related networks (gastric mill [chewing, [~]0.1 Hz]; pyloric [filtering food, [~]1 Hz]). Here, we investigate coordination between these networks during the Gly1-SIFamide (SIF) neuropeptide modulatory state. SIF activates a unique triphasic gastric mill rhythm in which the typically pyloric-only LPG neuron generates dual pyloric-plus gastric mill-timed oscillations. Additionally, the pyloric rhythm exhibits increased cycle frequency during gastric mill rhythm-timed LPG bursts, and decreased cycle frequency during IC, or IC plus LG gastric mill neuron bursts. Hyperpolarizing current injections and photoinactivation of network neurons demonstrate that gastric mill rhythm bursts in IC, but not LG, are responsible for decreasing the pyloric frequency, whereas LPG increases pyloric frequency through its rectified electrical coupling to pyloric pacemaker neurons. Surprisingly, LPG photoinactivation also eliminated slowing of the pyloric rhythm. IC firing frequency and gastric mill burst duration were not altered by LPG photoinactivation, suggesting that IC slows the pyloric rhythm primarily via synaptic inhibition of LPG, which then slows the pyloric pacemakers via electrical coupling. Thus, despite its rectification, an electrical synapse directly conveys endogenous bursting and indirectly funnels neurotransmitter-mediated inhibition to enable one network to alternately increase and decrease the frequency of a related network.

Significance StatementRelated rhythmic behaviors frequently exhibit coordination, yet the cellular mechanisms coordinating the underlying neural networks are not determined in most systems. We investigated coordination between two small, well-characterized crustacean feeding-associated networks during a neuropeptide-elicited modulatory state. We find that a dual fast/slow network neuron directly increases fast network frequency during its slow, intrinsically generated bursts, via electrical coupling to fast network pacemakers, despite rectification favoring the opposite direction. Additionally, the fast network is indirectly slowed during another slow-network phase, via chemical synaptic inhibition funneled through the same electrical synapse. Thus, a rectifying electrical synapse alternately reinforces and diminishes neuropeptide actions, enabling distinct frequencies of a faster network across different phases of a related slower rhythm.

Convergent effects of different anesthetics are due to changes in phase alignment of cortical oscillations
Many different anesthetics cause loss of responsiveness despite having diverse underlying molecular and circuit actions. To explore the convergent effects of these drugs, we examined how ketamine, an N-methyl-D-aspartate (NMDA) receptor antagonist, and dexmedetomidine, an 2 adrenergic receptor agonist, affected neural oscillations in the prefrontal cortex of nonhuman primates. Previous work has shown that anesthesia increases phase locking of low-frequency local field potential activity across cortex. We observed similar increases with anesthetic doses of ketamine and dexmedetomidine in the ventrolateral and dorsolateral prefrontal cortex, within and across hemispheres. However, the nature of the phase locking varied between regions. We found that oscillatory activity in different prefrontal subregions within each hemisphere became more anti-phase with both drugs. Local analyses within a region suggested that this finding could be explained by broad cortical distance-based effects, such as a large traveling wave. By contrast, homologous areas across hemispheres increased their phase alignment. Our results suggest that the drugs induce strong patterns of cortical phase alignment that are markedly different from those in the awake state, and that these patterns may be a common feature driving loss of responsiveness from different anesthetic drugs.

Effects of context changes on memory reactivation
The efficient utilization of limited working memory (WM) resources involves transferring task-relevant information to long-term memory (LTM) through repetition. While the interaction between context and LTM has been extensively studied, its influence on the dynamics between WM and LTM is less understood. In this study, we explored these dynamics using a delayed match-to-sample task, where participants encountered the same target object across six consecutive trials, facilitating the transition from WM to LTM. Notably, during half of these target repetitions, the background color changed. To measure the WM storage of the target, we analyzed the contralateral delay activity (CDA) in electroencephalography (EEG). Our results showed that a task-irrelevant context change triggers the reactivation of LTM in WM. This reactivation may be attributed to content-context binding in WM and hippocampal pattern separation.

Comparing the effect of multi gradient echo and multi band fMRI during a semantic task
The Blood Oxygenation Level Dependent (BOLD) signal, as measured using functional magnetic resonance imaging (fMRI), is known to vary in sensitivity across the brain due to magnetic susceptibility artefacts. In particular, the ventral anterior temporal lobes (vATL) have been implicated with semantic cognition using convergent methods (i.e., neuropsychology, PET, MEG, brain stimulation) but less so with fMRI using conventional gradient-echo protocols. There are methods to alleviate signal loss but multi-echo fMRI has gained popularity. Here, additional volumes are collected that span across a range of T2* values, however, this results sub-optimum parameters (i.e., repetition times, resolution, acceleration). "Multi-band" imaging has been used with multi-echo to speed up data acquisition; however, it is unclear how these modifications contribute to fMRI sensitivity across the brain and for univariate/multivariate analyses. In the current study, we used a factorial design where we manipulated the echo and/or band to assess how well the semantic network can be detected. When comparing the precision with which activations were detected (i.e, average T-statistics), we found that multi-band protocols were beneficial, with no evidence of signal leakage artefacts. When comparing the magnitude of activations, multi-echo protocols increased activations in regions prone to susceptibility artefacts (specifically the anterior temporal lobes, ATLs). Both multi-banding and independent component analysis (ICA)-denoising of multi-echo data tended to improve multi-voxel decoding of conditions. However, multi-echo protocols reduced activation magnitude in more central regions, such as the medial temporal lobes, possibly due to higher in-plane acceleration required to collect multiple-echoes. Nonetheless, the multi-echo multi-band protocol is a promising default option for fMRI on most regions, particularly those that suffer from susceptibility artefacts, as well as offering the potential to apply advanced post-processing methods to take advantage of the increased temporal (or spatial) resolution of multi-band protocols and more principled ICA-denoising based on TE-dependence of BOLD signals.

Ultrasound as a reliable guide for lumbar intrathecal injection in rats: A pilot study
Lumbar intrathecal administration provides an ideal route for drug delivery into the central nervous system, especially when dorsal root ganglions are the main target for the therapy in rat model of chronic pain. Two main methods of lumbar intrathecal administrations are chronic catheter implantation and the acute needle puncture. Chronic catheter implantation involves surgical manipulation to insert micro indwelling catheter into the intrathecal space. However, this method is invasive, produces inflammatory reactions, and generates more surgical stress. Acute needle puncture is less invasive and cheaper but is technically challenging to perform. We performed an ultrasound-guided lumbar intrathecal injection in six male Sprague Dawley rat cadavers, on average weighing 250-300 grams. Fresh rat cadavers were positioned in a sternal recumbent position, vertebrae were palpated and scanned using a linear probe ultrasound. A 25G needle insertion was advanced with real-timeultrasound guidance, and placement was confirmed prior to dye injection (Methylene blue, Sigma Aldrich). Cadavers were then dissected, and the vertebrae were visually inspected for dye staining. All three cadavers that underwent intrathecal injection with sagittal and axial plane ultrasound guidance showed positive dye staining within the intrathecal space, confirming successful acute intrathecal administration. There was one successful intrathecal injection under sagittal plane-only ultrasound guidance. Ultrasound is a useful, operator-dependent tool to guide acute needle puncture intrathecal administration.

Cell-Type Specific Reductions in Interneuron Gene Expression within Subregions of the Anterior and Posterior Cingulate Gyrus of Schizophrenia and Bipolar Disorder Subjects
Schizophrenia (SZ) and bipolar disorder (BP) patients share overlapping and distinct neurocognitive deficits. Neuroimaging of these patients and postmortem gene expression analyses suggest that compromised cingulate gyrus GABA-ergic interneurons may contribute to cognitive impairments in SZ and BP. Therefore, we investigated potential gene expression signatures for SZ and BP using interneuron cell-type specific markers including glutamic acid decarboxylase (GAD67), parvalbumin (PV), somatostatin (SST), and vasoactive intestinal peptide (VIP) within cingulate Brodmanns areas (BA). We report reduced GAD67 mRNA in anterior midcingulate cortex (aMCC) of SZ and BP subjects with BA24c being most dysregulated across disorders, demonstrating reduced PV (SZ), SST (BP), and VIP mRNA (SZ and BP). Dorsal posterior cingulate (dPCC) displayed decreased SST (BP) whereas retrosplenial cortex (RSC) showed reduced PV (SZ and BP) and SST mRNA (BP). Our results show shared and unique transcription signatures of two disorders in specific cingulate gyrus regions and cell types. SZ and BP show a similar profile of aMCC gene expression reductions suggesting subregional dysregulation within areas associated with error/action monitoring and the saliency network. In dPCC/RSC, transcriptional changes are associated with disease-specific gene/subregion signatures, possibly underlying differential effects on allocation of attentional resources and visuospatial memory processing unique to each disorder.

Enhanced Working Memory Representations for Rare Events
Rare events (oddballs) produce a variety of enhanced physiological responses relative to frequent events (standards), including the P3b component of the event-related potential (ERP) waveform. Previous research has suggested that the P3b component is related to working memory, which implies that working memory representations will be enhanced for rare stimuli. To test this hypothesis, we devised a modified oddball paradigm in which the target was a disk presented at one of 16 different locations, which were divided into a rare set and a frequent set. Participants made a binary response on each trial to report whether the target appeared in the rare set or the frequent set. As expected, the P3b was much larger for stimuli appearing at a location within the rare set. We also included occasional probe trials in which the subject reported the exact location of the target. We found that these reports were more accurate for locations within the rare set than for locations within the frequent set. Moreover, the mean accuracy of these reports was correlated with the mean amplitude of the P3b. We also applied multivariate pattern analysis to the ERP data to "decode" the remembered location of the target. Decoding accuracy was greater for locations within the rare set than for locations within the frequent set. These behavioral and electrophysiological results demonstrate that although both frequent and rare events are stored in working memory, the representations are enhanced for rare events.

Significance StatementFor many decades, researchers have observed that rare events elicit a broad range of physiological responses, and there has been much speculation about the functional significance of these responses. One such response is the P3b component, which is a large voltage deflection in scalp EEG recordings. Over 40 years ago, the P3b was hypothesized to reflect "context updating" (now often called "working memory updating"). However, there has been no direct evidence that working memory is actually enhanced for rare, P3b-eliciting events. In the present study, we found that both behavioral and electrophysiological measures of working memory were enhanced for rare events. This is potentially related to the release of norepinephrine across the cortex.

Autonomic Nervous System activity correlates with peak experiences induced by DMT and predicts increases in wellbeing
Non-ordinary states of consciousness induced by psychedelics can be accompanied by so-called peak experiences, characterized at the emotional level by their intensity and positive valence. These experiences are strong predictors of positive outcomes following psychedelic-assisted therapy, and it is therefore important to better understand their biology. Despite growing evidence that the autonomic nervous system (ANS) plays an important role in mediating emotional experiences, its involvement in the psychedelic experience is poorly understood. The aim of this study was to investigate to what extant changes in the relative influence of the sympathetic (SNS) and parasympathetic nervous systems (PNS) over cardiac activity may reflect the subjective experience induced by the short-acting psychedelic N,N-Dimethyltryptamine (DMT). We derived measures of SNS and PNS activity from the electrocardiogram data of 17 participants (11 males, 6 females, mean age = 33.8 y, SD = 8.3) while they received either DMT or placebo. Results show that the joint influence of SNS and PNS ( sympatho-vagal coactivation) over cardiac activity was robustly correlated with participants ratings of Spiritual Experience and Insightfulness during the DMT experience, while also being related to improved wellbeing scores two weeks after the session. In addition, we found that the state of balance between the two ANS branches ( sympatho-vagal balance) before DMT injection predicted scores of Insightfulness during the DMT experience. These findings demonstrate the important involvement of the ANS in psychedelic-induced peak experiences and may pave the way to the development of biofeedback-based tools to enhance psychedelic-therapy.

Significance statementPsychedelics can give rise to intense positive subjective experiences - aligned with Maslows notion of peak experiences - that can have a positive and enduring impact on mental health. Understanding how these experiences relate to peripheral physiology before and during the acute effects of psychedelics is an important object of enquiry, as it may help advance the therapeutic use of these compounds. In this study, we demonstrate that specific peripheral states computed from heart rate activity recordings predicted and correlated with acute peak experiences and increases in wellbeing. These findings have implications for the relationship between peripheral physiology and altered states of consciousness. Moreover, they highlight a putative marker of physiological readiness prior the psychedelic experience that could predict therapeutically relevant mechanisms that might be modified to improve mental health outcomes in psychedelic-therapy.

Reduced STMN2 and pathogenic TDP-43, two hallmarks of ALS, synergize to accelerate motor decline in mice
Pathological TDP-43 loss from the nucleus and cytoplasmic aggregation occurs in almost all cases of ALS and half of frontotemporal dementia patients. Stathmin2 (Stmn2) is a key target of TDP-43 regulation and aberrantly spliced Stmn2 mRNA is found in patients with ALS, frontotemporal dementia, and Alzheimers Disease. STMN2 participates in the axon injury response and its depletion in vivo partially replicates ALS-like symptoms including progressive motor deficits and distal NMJ denervation. The interaction between STMN2 loss and TDP-43 dysfunction has not been studied in mice because TDP-43 regulates human but not murine Stmn2 splicing. Therefore, we generated trans-heterozygous mice that lack one functional copy of Stmn2 and express one mutant TDP-43Q331K knock-in allele to investigate whether reduced STMN2 function exacerbates TDP-43-dependent pathology. Indeed, we observe synergy between these two alleles, resulting in an early onset, progressive motor deficit. Surprisingly, this behavioral defect is not accompanied by detectable neuropathology in the brain, spinal cord, peripheral nerves or at neuromuscular junctions (NMJs). However, the trans-heterozygous mice exhibit abnormal mitochondrial morphology in their distal axons and NMJs. As both STMN2 and TDP-43 affect mitochondrial dynamics, and neuronal mitochondrial dysfunction is a cardinal feature of many neurodegenerative diseases, this abnormality likely contributes to the observed motor deficit. These findings demonstrate that partial loss of STMN2 significantly exacerbates TDP-43-associated phenotypes, suggesting that STMN2 restoration could ameliorate TDP-43 related disease before the onset of degeneration.

Loss of prohibitin 2 in Schwann cells dysregulates key transcription factors controlling developmental myelination
Schwann cells are critical for the proper development and function of the peripheral nervous system, where they form a mutually beneficial relationship with axons. Past studies have highlighted that a pair of proteins called the prohibitins play major roles in Schwann cell biology. Prohibitins are ubiquitously expressed and versatile proteins. We have previously shown that while prohibitins play a crucial role in Schwann cell mitochondria for long-term myelin maintenance and axon health, they may also be present at the Schwann cell-axon interface during development. Here, we expand on this work, showing that drug-mediated modulation of prohibitins in vitro disrupts myelination and confirming that Schwann cell-specific ablation of prohibitin 2 (Phb2) in vivo results in early and severe defects in peripheral nerve development. Using a proteomic approach in vitro, we identify a pool of candidate PHB2 interactors that change their interaction with PHB2 depending on the presence of axonal signals. Furthermore, we show in vivo that loss of Phb2 in mouse Schwann cells causes ineffective proliferation and dysregulation of transcription factors EGR2 (KROX20), POU3F1 (OCT6) and POU3F2 (BRN2) that are necessary for proper Schwann cell maturation. Schwann cell-specific deletion of Jun, a transcription factor associated with negative regulation of myelination, confers partial rescue of the development defect seen in mice lacking Schwann cell Phb2. This work develops our understanding of Schwann cell biology, revealing that Phb2 may directly or indirectly modulate the timely expression of transcription factors necessary for proper peripheral nervous system development, and proposing candidates that may play a role in PHB2-mediated integration of axon signals in the Schwann cell.

The effect of corticosterone on the acquisition of Pavlovian conditioned approach behavior is dependent on sex and vendor
Cues in the environment become predictors of biologically relevant stimuli, such as food, through associative learning. These cues can not only act as predictors but can also be attributed with incentive motivational value and gain control over behavior. When a cue is imbued with incentive salience, it attains the ability to elicit maladaptive behaviors characteristic of psychopathology. We can capture the propensity to attribute incentive salience to a reward cue in rats using a Pavlovian conditioned approach paradigm, in which the presentation of a discrete lever-cue is followed by the delivery of a food reward. Upon learning the cue-reward relationship, some rats, termed sign-trackers, develop a conditioned response directed towards the lever-cue; whereas others, termed goal-trackers, approach the food cup upon lever-cue presentation. Here, we assessed the effects of systemic corticosterone (CORT) on the acquisition and expression of sign- and goal-tracking behaviors in male and female rats, while examining the role of the vendor (Charles River or Taconic) from which the rats originated in these effects. Male and female rats from Charles River had a greater tendency to sign-track than those from Taconic. Administration of CORT enhanced the acquisition of sign-tracking behavior in males from Charles River and females from both vendors. Conversely, administration of CORT had no effect on the expression of the conditioned response. These findings demonstrate a role for CORT in cue-reward learning and suggest that inherent tendencies towards sign- or goal-tracking may interact with this physiological mediator of motivated behavior.

HighlightsO_LIMale and female rats from Charles River exhibit more sign-tracking relative to those from Taconic.
C_LIO_LICorticosterone increases the acquisition of sign-tracking in male rats from Charles River.
C_LIO_LICorticosterone increases the acquisition of sign-tracking in female rats, regardless of vendor.
C_LIO_LIThere is no effect of corticosterone on the expression of sign-tracking behavior in either male or female rats.
C_LI

Decoding Continuous Character-based Language from Non-invasive Brain Recordings
Deciphering natural language from brain activity through non-invasive devices remains a formidable challenge. Previous non-invasive decoders either require multiple experiments with identical stimuli to pinpoint cortical regions and enhance signal-to-noise ratios in brain activity, or they are limited to discerning basic linguistic elements such as letters and words. We propose a novel approach to decoding continuous language from single-trial non-invasive fMRI recordings, in which a three-dimensional convolutional network augmented with information bottleneck is developed to automatically identify responsive voxels to stimuli, and a character-based decoder is designed for the semantic reconstruction of continuous language characterized by inherent character structures. The resulting decoder can produce intelligible textual sequences that faithfully capture the meaning of perceived speech both within and across subjects, while existing decoders exhibit significantly inferior performance in cross-subject contexts. The ability to decode continuous language from single trials across subjects demonstrates the promising applications of non-invasive language brain-computer interfaces in both healthcare and neuroscience.

Inflammasome-Inhibiting Nanoligomers are Neuroprotective Against Space-Induced Pathology in Healthy and Diseased 3D Human Motor and Pre-Frontal Cortex Brain Organoids
Microgravity and space environment has been linked to deficits in neuromuscular and cognitive capabilities, hypothesized to occur due to accelerated aging and neurodegeneration in space. While the specific mechanisms are still being investigated, spaceflight-associated neuropathology is an important health risk to space astronauts and tourists, and is being actively investigated for the development of appropriate countermeasures. However, such space-induced neuropathology offers an opportunity for accelerated screening of therapeutic targets and lead molecules for treating neurodegenerative diseases. Here we show, a proof-of-concept high-throughput target screening (on Earth), target validation, and mitigation of microgravity-induced neuropathology using our Nanoligomer platform, onboard the 43-day SpaceX CRS-29 mission to the International Space Station (ISS). First, comparing 3D healthy and diseased pre-frontal cortex (PFC, for cognition) and motor neuron (MN, for neuromuscular function) organoids, we assessed space-induced pathology using biomarkers relevant to Alzheimers Disease (AD), Frontotemporal Dementia (FTD), and Amyotrophic Lateral Sclerosis (ALS). Both healthy and diseased PFC and MN organoids showed significantly enhanced neurodegeneration in space, as measured through relevant disease biomarkers, when compared to their respective Earth controls. Second, we tested the top two lead molecules, NI112 which targeted NF-{kappa}B, and NI113 that targeted IL-6. We observed that these Nanoligomers significantly mitigate the AD, FTD, and ALS relevant biomarkers like amyloid beta-42 (A{beta}42), phosphorylated Tau (pTau), Kallikrein (KLK-6), Tar DNA-binding protein 43 (TDP-43), and others. Moreover, the 43-day Nanoligomer treatment of these brain organoids did not appear to cause any observable toxicity or safety issues in the target organoid tissue, suggesting good tolerability for these molecules in the brain at physiologically relevant doses. Together, these results show significant potential for both the development and translation of NI112 and NI113 molecules as potential neuroprotective countermeasures for safer space travel, and demonstrate the usefulness of the space environment for rapid, high-throughput screening of targets and lead molecules for clinical translation. We assert that the use of microgravity in drug development and screening may ultimately benefit millions of patients suffering from debilitating neurodegenerative diseases on Earth.

Mitochondrial pyruvate transport regulates presynaptic metabolism and neurotransmission
Glucose has long been considered the primary fuel source for the brain. However, glucose levels fluctuate in the brain during sleep, intense circuit activity, or dietary restrictions, posing significant metabolic stress. Here, we demonstrate that the mammalian brain utilizes pyruvate as a fuel source, and pyruvate can support neuronal viability in the absence of glucose. Nerve terminals are sites of metabolic vulnerability within a neuron and we show that mitochondrial pyruvate uptake is a critical step in oxidative ATP production in hippocampal terminals. We find that the mitochondrial pyruvate carrier is post-translationally modified by lysine acetylation which in turn modulates mitochondrial pyruvate uptake. Importantly, our data reveal that the mitochondrial pyruvate carrier regulates distinct steps in synaptic transmission, namely, the spatiotemporal pattern of synaptic vesicle release and the efficiency of vesicle retrieval, functions that have profound implications for synaptic plasticity. In summary, we identify pyruvate as a potent neuronal fuel and mitochondrial pyruvate uptake as a critical node for the metabolic control of synaptic transmission in hippocampal terminals.

HIGHLIGHTSO_LISerum pyruvate is taken up by the brain and efficiently oxidized in the TCA cycle.
C_LIO_LIThe mitochondrial pyruvate carrier (MPC) is essential for presynaptic energy metabolism.
C_LIO_LIAcetylation of the MPC complex modulates mitochondrial pyruvate uptake.
C_LIO_LIMPC activity regulates the release and retrieval of synaptic vesicles in nerve terminals.
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Identifying EEG Biomarkers of Depression with Novel Explainable Deep Learning Architectures
Deep learning methods are increasingly being applied to raw electro-encephalogram (EEG) data. However, if these models are to be used in clinical or research contexts, methods to explain them must be developed, and if these models are to be used in research contexts, methods for combining explanations across large numbers of models must be developed to counteract the inherent randomness of existing training approaches. Model visualization-based explainability methods for EEG involve structuring a model architecture such that its extracted features can be characterized and have the potential to offer highly useful insights into the patterns that they uncover. Nevertheless, model visualization-based explainability methods have been underexplored within the context of multichannel EEG, and methods to combine their explanations across folds have not yet been developed. In this study, we present two novel convolutional neural network-based architectures and apply them for automated major depressive disorder diagnosis. Our models obtain slightly lower classification performance than a baseline architecture. However, across 50 training folds, they find that individuals with MDD exhibit higher {beta} power, potentially higher {delta} power, and higher brain-wide correlation that is most strongly represented within the right hemisphere. This study provides multiple key insights into MDD and represents a significant step forward for the domain of explainable deep learning applied to raw EEG. We hope that it will inspire future efforts that will eventually enable the development of explainable EEG deep learning models that can contribute both to clinical care and novel medical research discoveries.