bioRxiv Subject Collection: Neuroscience's Journal

Objective Markers of Sustained Attention Fluctuate Independently of Mind-Wandering Reports
Sustained attention fluctuates between periods of good and poor attentional performance. Two major methodologies exist to study these fluctuations: an objective approach that identifies "in-the-zone" states of consistent response times (RTs) and "out-of-the-zone" states of erratic RTs and a subjective approach that asks participants whether they are on-task or mind wandering. Although both approaches effectively predict attentional lapses, it remains unclear whether they capture the same or distinct attentional fluctuations. We combined both approaches within a single sustained attention task requiring frequent responses and response inhibition to rare targets to explore their consistency (N=40). Behaviorally, both objective out-of-the-zone and subjective mind-wandering states were associated with more attentional lapses. However, the percentage of time spent out-of-the-zone did not differ between on-task and mind-wandering periods and both objective and subjective states independently predicted error-proneness, suggesting that the two methods do not capture the same type of attention fluctuations. Whereas attentional preparation before correct inhibitions was greater during out-of-the-zone compared to in-the-zone periods, preparation did not differ by subjective state. In contrast, post-error slowing differed by both objective and subjective states, but in opposite directions: slowing was observed when participants were objectively out-of-the-zone or subjectively on-task. Overall, our results provide evidence that objective and subjective approaches capture distinct attention fluctuations during sustained attention tasks. Integrating both objective and subjective measures is crucial for fully understanding the mechanisms underlying our ability to remain focused.

Co-activation of selective nicotinic acetylcholine receptor subtypes is required to reverse hippocampal network dysfunction and prevent fear memory loss in Alzheimer's disease
Alzheimer's disease (AD) is the most common form of dementia with no known cause and cure. Research suggests that a reduction of GABAergic inhibitory interneurons' activity in the hippocampus by beta-amyloid peptide (A{beta}) is a crucial trigger for cognitive impairment in AD via hyperexcitability. Therefore, enhancing hippocampal inhibition is thought to be protective against AD. However, hippocampal inhibitory cells are highly diverse, and these distinct interneuron subtypes differentially regulate hippocampal inhibitory circuits and cognitive processes. Moreover, A{beta} unlikely affects all subtypes of inhibitory interneurons in the hippocampus equally. Hence, identifying the affected interneuron subtypes in AD to enhance hippocampal inhibition optimally is conceptually and practically challenging. We have previously found that A{beta} selectively binds to two of the three major hippocampal nicotinic acetylcholine receptor (nAChR) subtypes, 7- and 4{beta}2-nAChRs, but not 3{beta}4-nAChRs, and inhibits these two receptors in cultured hippocampal inhibitory interneurons to decrease their activity, leading to hyperexcitation and synaptic dysfunction in excitatory neurons. We have also revealed that co-activation of 7- and 4{beta}2-nAChRs is required to reverse the A{beta}-induced adverse effects in hippocampal excitatory neurons. Here, we discover that 7- and 4{beta}2-nAChRs predominantly control the nicotinic cholinergic signaling and neuronal activity in hippocampal parvalbumin-positive (PV+) and somatostatin-positive (SST+) inhibitory interneurons, respectively. Furthermore, we reveal that co-activation of these receptors is necessary to reverse hippocampal network dysfunction and fear memory loss in the amyloid pathology model mice. We thus suggest that co-activation of PV+ and SST+ cells is a novel strategy to reverse hippocampal dysfunction and cognitive decline in AD.

Development of a DSM test battery to determine depression-like marmoset
Depression is a serious and high-incidence mental disorder that can lead to suicide. Despite much depression research using humans and rodents to date, it has been difficult to completely overcome depression and elucidate its etiology. Marmoset monkeys have been utilized to study neuropsychiatric disorders in recent years. Since the clinical diagnostic criteria for psychiatric disorders are mainly based on multiple behavioral changes, test battery systems, a multifaceted and comprehensive strategy, are applied to depression research. Here, we devised a test battery with six tests to investigate depression-like symptoms corresponding to clinical criteria and set criteria for a test indicator-based judgment. We did a usability confirmation experiment using a drug and judged three of nine marmosets as depression-like. This rate is comparable with the incidence rate of human patients; i.e., 10-30% of patients who received reserpine treatment suffer from depression. Thus, we propose the test battery we constructed in this study will contribute to the study of depression.

Aberrant remodelling of astrocytic architecture in acute hepatic encephalopathy: complexity of oedematic atrophic astrocytes
Hepatic encephalopathy (HE) following acute liver failure (ALF) is a primary toxic astrocytopathy, although in-depth characterisation of underlying pathogenesis is far from complete. Among the multitude of astrocyte-specific proteins guiding brain functionality, plasmalemma-cytoskeletal linker ezrin, actin-binding protein profilin-1, and water channel aquaporin 4 (AQP4) contribute to astrocytic morphological plasticity through regulation of cell shape, volume, complexity of primary and terminal processes, and positioning astrocytes against other CNS constituents. Changes in these proteins might contribute to the brain oedema and astrocytic morphological remodelling in the HE. Using transmission electron microscopy, confocal fluorescent microscopy, and 3D reconstruction, we found complex morphological alterations of cortical astrocytes in mice with azoxymethane-induced ALF. Astrocytic primary branches demonstrated hypertrophy, whereas terminal leaflets showed atrophy quantified by the reduced area occupied by astrocytes, decreased number and the length of leaflets, decreased leaflets volume fraction, and altered astrocyte-to-neurone landscape. These morphological changes correlat with decreased expression of AQP4, phosphorylated leaflet-associated ezrin, and the actin dynamics regulator, profilin 1, suggesting the contribution of these proteins to astrocytic pathological remodelling. Pathological changes in astrocytes develop in parallel, and are likely causally linked to, the HE-linked neurological decline, manifested by a reduction in electroencephalography power and by excessive glutamate in the brain microdialysates.

Degradation in Binaural and Spatial Hearing and Auditory Temporal Processing Abilities as a Function of Aging
Objectives: Sensorineural hearing loss is common with advancing age, but even when hearing is normal or near normal in older persons, performance deficits are often seen for suprathreshold listening tasks such as understanding speech in background noise or localizing the direction sounds are coming from. This suggests there is also a more central source of the problem. Objectives of this study were to examine as a function of age (young adult to septuagenarian) performance on: 1) a spatial acuity task examining lateralization ability, and a spatial speech-in-noise (SSIN) recognition task, both measured in a hemi-anechoic sound field using a circular horizontal-plane loudspeaker array, and 2) a suprathreshold auditory temporal processing task and a spectro-temporal processing task, both measured under headphones. Further, we examined any correlations between the measures. Design: Subjects were 48 adults, aged 21 to 78, with either normal hearing or only a mild sensorineural hearing loss through 4000 Hz. The lateralization task measured minimum audible angle (MAA) for 500 and 4000 Hz narrowband noise (NBN) bursts in diffuse background noise for both an on-axis (subject facing 0{ring}) and off-axis (facing 45{ring}) listening condition at signal-to-noise ratios (SNRs) of -3, -6, -9, and -12 dB. For 42 of the subjects, SSIN testing was also completed for key word recognition in sentences in multi-talker babble noise; specifically, the separation between speech and noise loudspeakers was adaptively varied to determine the difference needed for 40% and 80% correct performance levels. Finally, auditory temporal processing ability was examined using the Temporal Fine Structure test (44 subjects), and the Spectro-Temporal Modulation test (46 subjects). Results: Mean lateralization performances were poorer (larger MAAs) in older compared to younger subjects, particularly in the more adverse listening conditions (i.e., for 4000 Hz, off-axis, and at poorer SNRs). Performance variability was notably higher for older subjects than for young adults. The 4000 Hz NBN bursts produced larger MAAs than did 500 Hz NBN bursts. The SSIN data also showed declining mean performance with age at both criterion levels, with greater variability again found for older subjects. Spearman rho analyses revealed some low to moderate, but significant correlation coefficients for age versus MAA and for age versus SSIN results. Results from both the TFS and STM showed decreased mean performance with aging, and revealed moderate, significant correlations, with the strongest relationship shown with the TFS test. Finally, of note, extended-high-frequency (EHF) hearing loss (measured between 9000 and 16,000 Hz) was found to increase with aging, but was not seen in the young adult subjects. Conclusions: Particularly for more adverse listening conditions, age-related deficits were found on both of the spatial hearing tasks and in temporal and spectro-temporal processing abilities. It may be that deficits in temporal processing ability contribute to poorer spatial hearing performance in older subjects due to inaccurate coding of binaural/interaural timing information sent from the periphery to the brainstem. In addition, EHF hearing loss may be a coexisting factor that impacts performance in older subjects.

A multi-region recurrent circuit for evidence accumulation in rats
Decision-making based on noisy evidence requires accumulating evidence and categorizing it to form a choice. Here we evaluate a proposed feedforward and modular mapping of this process in rats: evidence accumulated in anterodorsal striatum (ADS) is categorized in prefrontal cortex (frontal orienting fields, FOF). Contrary to this, we show that both regions appear to be indistinguishable in their encoding/decoding of accumulator value and communicate this information bidirectionally. Consistent with a role for FOF in accumulation, silencing FOF to ADS projections impacted behavior throughout the accumulation period, even while nonselective FOF silencing did not. We synthesize these findings into a multi-region recurrent neural network trained with a novel approach. In-silico experiments reveal that multiple scales of recurrence in the cortico-striatal circuit rescue computation upon nonselective FOF perturbations. These results suggest that ADS and FOF accumulate evidence in a recurrent and distributed manner, yielding redundant representations and robustness to certain perturbations.

Cell-Type-Specific Regulation of Cocaine Reward by the E2F3a Transcription Factor in Nucleus Accumbens
The development of drug addiction is characterized by molecular changes in brain reward regions that lead to the transition from recreational to compulsive drug use. These neurobiological processes in brain reward regions, such as the nucleus accumbens (NAc), are orchestrated in large part by transcriptional regulation. Our group recently identified the transcription factor E2F3a as a novel regulator of cocaine's rewarding effects and gene expression regulation in the NAc of male mice. Despite this progress, no information is available about the role of E2F3a in regulating cocaine reward at the sex- and cell-specific levels. Here, we used male and female mice expressing Cre-recombinase in either D1- or D2-type medium spiny neurons (MSNs) combined with viral-mediated gene transfer to bidirectionally control levels of E2F3a in a cell-type-specific manner in the NAc during conditioned place preference (CPP) to cocaine. Our findings show that selective overexpression of E2F3a in D1-MSNs increased cocaine CPP in both male and female mice, whereas opposite effects were observed under knockdown conditions. In contrast, equivalent E2F3a manipulations in D2-MSNs had no significant effects. To further explore the role of E2F3a in sophisticated operant and motivated behaviors, we performed viral manipulations of all NAc neurons in combination with cocaine self-administration and behavioral economics procedures in rats and demonstrated that E2F3a regulates sensitivity aspects of cocaine seeking and taking. These results confirm E2F3a as a central substrate of cocaine reward and demonstrate that this effect is mediated in D1-MSNs, thereby providing increased knowledge of cocaine action at the transcriptional level.

High-speed three-dimensional random access scanning with SPARCLS
High-speed volumetric imaging is crucial for observing fast and distributed processes such as neuronal activity. Multiphoton microscopy helps to mitigate scattering effects inside tissue, but the standard raster scanning approach limits achievable volume rates. Random-access scanning can lead to a considerable speed-up by sampling only pre-selected locations, but existing techniques based on acousto-optic deflectors are still limited to a point rate of up to ~50 kHz. This limits the number of parallel targets at the high acquisition rates necessary, for example, in voltage imaging or imaging of fast synaptic events. Here we introduce SPARCLS, a method for 3D random-access scanning at up to 340 kHz point rate using a single 1D phase modulator. We show the potential of this method by imaging synaptic events with fluorescent glutamate sensors in mammalian organotypic slices as well as in zebrafish larvae.

Interoceptive Signals Bias Decision Making in Rhesus Macaques
Several influential theories have proposed that interoceptive signals, sent from the body to the brain, contribute to neural processes that coordinate complex behaviors. Using pharmacological agents that do not cross the blood-brain barrier, we altered interoceptive states and evaluated their effect on decision-making in rhesus monkeys. We used glycopyrrolate, a non-specific muscarinic (parasympathetic) antagonist, and isoproterenol, a beta-1/2 (sympathetic) agonist, to create a sympathetic-dominated physiological state indexed by increased heart rate. Rhesus monkeys were trained on two variants of an approach-avoidance conflict task, where they chose between enduring mildly aversive stimuli in exchange for a steady flow of rewards, or cancelling the aversive stimuli, forgoing the rewards. The delay to interrupt the aversive stimuli and the reward were used as a measure of the cost-benefit estimation that drove the monkeys' decisions. Both drugs altered approach-avoidance decisions, substantially reducing the delay to interrupt the aversive stimuli. To determine whether this autonomic state lowered tolerance to aversive stimuli or reduced the subjective value of the reward, we tested the effects of glycopyrrolate on a food preference task. Food preference was unaltered, suggesting that the sympathetic dominated state selectively reduces tolerance for aversive stimuli without altering reward-seeking behaviors. As these drugs have no direct effect on brain physiology, interoceptive afferents are the most likely mechanism by which decision making was biased toward avoidance.

Translating human drug use patterns into rat models: exploring spontaneous interindividual differences via refined drug self-administration procedures
Users of heroin and cocaine self-regulate the dosage and frequency of administration to experience drugs' rewarding effects and avoid withdrawal. In contrast, most preclinical self-administration and choice procedures use experimenter-imposed unit-doses and timeout after infusions. Here, we introduce a no-timeout procedure that overcomes this limitation. We analyzed the heroin and cocaine taking- and seeking-patterns and estimated drug-brain levels in the presence or absence of timeout between drug injections. We further assessed the effect of timeout and drug or social peer access time on drug preference. Removing the timeout had a profound effect on pattern of heroin taking and seeking, promoting the emergence of burst-like drug intake. Timeout removal had a modest effect on cocaine taking and seeking. Drug or social peer access time increased heroin but not cocaine preference. Removal of timeout during self-administration and increasing the access time during choice resulted in a self-administration procedure that more closely mimic human heroin intake, offering a platform to identify novel medications.

Dynamic control of neural manifolds
In the central nervous system, sequences of neural activity form trajectories on low dimensional neural manifolds. The neural computation underlying flexible cognition and behavior relies on dynamic control of these structures. For example different tasks or behaviors are represented on different subspaces, requiring fast timescale subspace rotation to move from one behavior to the next. For flexibility in a particular behavior, the neural trajectory must be dynamically controllable within that behaviorally determined subspace. To understand how dynamic control of neural trajectories and their underlying subspaces may be implemented in neural circuits, we first characterized the relationship between features of neural activity sequences and aspects of the low dimensional projection. Based on this, we propose neural mechanisms that can act within local circuits to modulate activity sequences thereby controlling neural trajectories in low dimensional subspaces. In particular, we show that gain modulation and transient synaptic currents control the speed and path of neural trajectories and clustered inhibition determines manifold orientation. Together, these neural mechanisms may enable a substrate for fast timescale computation on neural manifolds.

Detrimental Influence of Arginase-1 in Infiltrating Macrophages on Post-Stroke Functional Recovery and Inflammatory Milieu
Post-stroke inflammation critically influences functional outcomes following ischemic stroke. Arginase-1 (Arg1) is conventionally understood as a marker for anti-inflammatory macrophages, associated with the resolution of inflammation and promotion of tissue repair in various pathological conditions. However, its specific role in post-stroke recovery remains to be elucidated. This study investigates the functional impact of Arg1 expressed in macrophages on post-stroke recovery and inflammatory milieu. We observed a time-dependent increase in Arg1 expression, peaking at 7 days after photothrombotic stroke in mice. Cellular mapping analysis revealed that Arg1 was predominantly expressed in LysM-positive infiltrating macrophages. Using a conditional knockout (cKO) mouse model, we examined the role of Arg1 expressed in infiltrating macrophages. Contrary to its presumed beneficial effects, Arg1 cKO in LysM-positive macrophages significantly improved skilled forelimb motor function recovery after stroke. Mechanistically, Arg1 cKO attenuated fibrotic scar formation, enhanced peri-infarct remyelination, and increased synaptic density while reducing microglial synaptic elimination in the peri-infarct cortex. Gene expression analysis of FACS-sorted microglia revealed decreased TGF-{beta} signaling and pro-inflammatory cytokine activity in peri-infarct microglia from Arg1 cKO animals. In vitro co-culture experiments demonstrated that Arg1 activity in macrophages modulates microglial synaptic phagocytosis, providing evidence for macrophage-microglia interaction. These findings provide new insights into Arg1 function in CNS injury and highlight an interaction between infiltrating macrophages and resident microglia in shaping the post-stroke inflammatory milieu. Our study identifies Arg1 in macrophages as a potential therapeutic target for modulating post-stroke inflammation and improving functional recovery.

Mineral Phase Changes During Intervertebral Disc Degeneration
Intervertebral disc disease is a common cause of pain and neurological deficits and is known to be associated with degeneration and calcification. Here we analysed samples of herniated disc material and compared it to material taken from non-herniated discs following surgical treatment in dogs. Our clinical approach to these cases allows collection of samples providing a unique opportunity for a case-controlled study such as this, an opportunity which is not available to the human neurosurgeon. We analysed all samples using Fourier transform infrared (FTIR) spectroscopy, as well as a proportion with X-ray diffraction (XRD) and transmission electron microscopy (TEM). FTIR spectra of the majority of herniated samples were consistent with the presence of crystalline hydroxyapatite, whereas most of the non-herniated discs showed spectra consistent with amorphous phosphate material. XRD analysis and TEM confirmed these findings and identified the amorphous material as amorphous calcium phosphate nanoparticle clusters of [~] 20 nm diameter and the crystalline hydroxyapatite material as needles up to 100 nm in length.

The differences between the herniated and non-herniated discs indicate that the degenerative process involves a conversion of amorphous calcium phosphate into crystalline hydroxyapatite which precedes and may predispose the disc to herniate.

Spectral-switching analysis reveals real-time neuronal network representations of concurrent spontaneous naturalistic behaviors in human brain
Despite abundant evidence of functional networks in the human brain, their neuronal underpinnings, and relationships to real-time behavior have been challenging to resolve. Analyzing brain-wide intracranial-EEG recordings with video monitoring, acquired in awake subjects during clinical epilepsy evaluation, we discovered the tendency of each brain region to switch back and forth between 2 distinct power spectral densities (PSDs 2-55Hz). We further recognized that this spectral switching occurs synchronously between distant sites, even between regions with differing baseline PSDs, revealing long-range functional networks that would be obscured in analysis of individual frequency bands. Moreover, the real-time PSD-switching dynamics of specific networks exhibited striking alignment with activities such as conversation and hand movements, revealing a multi-threaded functional network representation of concurrent naturalistic behaviors. Network structures and their relationships to behaviors were stable across days, but were altered during N3 sleep. Our results provide a new framework for understanding real-time, brain-wide neural-network dynamics.

Newly discovered base barrier cells provide compartmentalization of choroid plexus, brain and CSF
The choroid plexus (ChP) is a highly understudied structure of the central nervous system (CNS). The structure hangs in the brain ventricles, is composed of an epithelial cell layer, which produces the cerebrospinal fluid (CSF) and forms the blood-CSF barrier. It encapsulates a stromal mix of fenestrated capillaries, fibroblasts and a broad range of immune cells. Here, we report that the ChP base region harbors unique fibroblasts that cluster together, are connected by tight junctions and seal the ChP stroma from brain and CSF, thereby forming ChP base barrier cells (ChP BBCs). ChP BBCs are derived from meningeal mesenchymal precursors, arrive early during embryonic development, are maintained throughout life and are conserved across species. Moreover, we provide transcriptional profiles and key markers to label ChP BBCs and observe a striking transcriptional similarity with meningeal arachnoid barrier cells (ABCs). Finally, we provide evidence that this fibroblast cluster functions as a barrier to control communication between CSF and the ChP stroma and between the latter and the brain parenchyma. Moreover, loss of barrier function was observed during an inflammatory insult. Altogether, we have identified a novel barrier that provides functional compartmentalization of ChP, brain and CSF.

GRAPHICAL ABSTRACT

O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=146 SRC="FIGDIR/small/601696v1_ufig1.gif" ALT="Figure 1">
View larger version (47K):
org.highwire.dtl.DTLVardef@2a782borg.highwire.dtl.DTLVardef@377b3eorg.highwire.dtl.DTLVardef@7c642eorg.highwire.dtl.DTLVardef@953fa6_HPS_FORMAT_FIGEXP M_FIG Newly discovered base barrier cells provide compartmentalization of choroid plexus, brain and CSF

The choroid plexus (ChP) hangs in the brain ventricles and is composed of an epithelial cell layer which produces the cerebrospinal fluid (CSF) and forms the blood-CSF barrier. The ChP epithelial cells are continuous with the ependymal cells lining the ventricle wall. At this base region, we identified and characterized a novel subtype of fibroblasts coined the ChP base barrier cells (BBCs). ChP BBCs express tight junctions (TJs), cluster together and seal the ChP stroma from CSF and brain parenchyma. The subarachnoid space (SAS) CSF penetrates deep into choroid plexus invaginations where it is halted by ChP BBCs.

Abbreviations: E9-16.5 (embryonic day 9-16.5); P1-4 (postnatal day 1-4).

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Prefrontal and ventral striatal dendritic morphology: effects of life-long complex housing and amphetamine administration
Complex housing is one of the most effective experiences in producing plastic changes in the brain. For example, animals living in complex environments show widespread synaptic changes both in cerebral cortex and the striatum. Similarly, repeatedly treating animals with psychomotor stimulants such as amphetamine also induces changes in prefrontal cortex and the striatum. The purpose of the current study was to determine the effects of life-long housing in complex environments versus standard laboratory caging and this experience influenced the later effects of amphetamine. Both male and female Long-Evans rats were placed in complex environments for about 110 days, beginning at conception, until adulthood at which time they were administered saline or amphetamine daily (1 mg/kg, IP) for 14 days. A week later the brains were harvested and processed for Golgi-Cox staining to analyze dendritic length, branching, and spine density in prefrontal cortex (areas Cg3 and AID) and Nucleus Accumbens (NAcc). The results showed that the prolonged period of enriched housing produced significant synaptic changes in all three measures in all three areas measured, but the effects differed in the two sexes. Amphetamine produced large synaptic changes in Cg3 and NAcc in males but only spine changes in those regions in females. Complex housing did not interact with the later effects of amphetamine administration. Thus, both complex housing and amphetamine can produce a range of synaptic changes depending upon sex and area examined. Furthermore, the effect of complex housing varies depending on the details of when complex housing is begun and how long it lasts.

Temporal resolution of spike coding in feedforward networks with signal convergence and divergence
Convergent and divergent structures in the networks that make up biological brains are found universally across many species and brain regions at various scales. Neurons in these networks fire action potentials, or "spikes", whose precise timing is becoming increasingly appreciated as large sources of information about both sensory input and motor output. While previous theories on coding in convergent and divergent networks have largely neglected the role of precise spike timing, our model and analyses place this aspect at the forefront. For a suite of stimuli with different timescales, we demonstrate that structural bottlenecks (small groups of neurons) post-synaptic to network convergence have a stronger preference for spike timing codes than expansion layers created by structural divergence. Additionally, we found that a simple network model with similar convergence and divergence ratios to those found experimentally can reproduce the relative contribution of spike timing information about motor output in the hawkmoth Manduca sexta. Our simulations and analyses suggest a relationship between the level of convergent/divergent structure present in a feedforward network and the loss of stimulus information encoded by its population spike trains as their temporal resolution decreases, which could be confirmed experimentally across diverse neural systems in future studies. We further show that this relationship can be generalized across different models and measures, implying a potentially fundamental link between network structure and coding strategy using spikes.

Behavioral and anatomical effects of complex rearing after day 7 neonatal frontal lesions vary with sex
Rats received medial frontal lesions, or sham surgery, on postnatal day 7 (P7), and were placed in complex environments or standard lab housing at weaning. Three months later the animals were tested in a spatial learning task and in a skilled reaching task. Rats with P7 lesions had smaller deficits in spatial learning than similar adult operates, and males performed better than females. Complex housing further improved the performance of male, but not female, lesion rats. The opposite was seen in motor performance as female lesion rats performed better than males and benefited from experience whereas males did not. There was a correlation between behavior and dendritic change as complex housing reversed lesion-induced dendritic atrophy, an effect that was greater in males. P7 frontal males, but not females, showed an increase in spine density that was reversed by complex housing. Experience thus can affect functional and anatomical outcome after early brain injury, but the effects vary with sex.

On the replicability of diffusion weighted MRI-based brain-behavior models
Establishing replicable inter-individual brain-wide associations is key to advancing our understanding of the crucial links between brain structure, function, and behavior, as well as applying this knowledge in clinical contexts. While the replicability and sample size requirements for anatomical and functional MRI-based brain-behavior associations have been extensively discussed recently, systematic replicability assessments are still lacking for diffusion-weighted imaging (DWI), despite it being the dominant non-invasive method to investigate white matter microstructure and structural connectivity. We report results of a comprehensive evaluation of the replicability of various DWI-based multivariate brain-behavior models. This evaluation is based on large-scale data from the Human Connectome Project, including five different DWI-based brain features (from fractional anisotropy to structural connectivity) and 58 different behavioral phenotypes. Our findings show an overall moderate replicability, with 24-31% of phenotypes replicable with sample sizes of fewer than 500. As DWI yields trait-like brain features, we restricted the analysis to trait-like phenotypes, such as cognitive and motor skills, and found much more promising replicability estimates, with 67-75% of these phenotypes replicable with n<500. Contrasting our empirical results to analytical replicability estimates substantiated that the replicability of DWI-based models is primarily a function of the true, unbiased effect size. Our work highlights the potential of DWI to produce replicable brain-behavior associations. However, it shows that achieving replicability with small-to-moderate samples requires stable, reliable and neurobiologically relevant target phenotypes. Our work highlights the potential of DWI to produce replicable brain-behavior associations, but only for stable, reliable and neurobiologically relevant target phenotypes.

HIGHLIGHTSO_LIModerate replicability in DWI-based models: Overall replicability of DWI-based brain-behavior associations ranges from 24-31% with sample sizes under 500.
C_LIO_LIImproved replicability for trait-like phenotypes: Trait-like phenotypes e.g., cognitive and motor skills exhibit higher replicability estimates of 67-75%, compared to state-like phenotypes such as emotion.
C_LIO_LIEffect size as a key factor: Replicability is primarily influenced by the true, unbiased effect size, highlighting the importance of targeting stable and reliable phenotypes.
C_LIO_LIPromise of -based multivariate associations: DWI-based brain-behaviour models should focus on phenotypes that display a sufficient temporal stability and test-retest reliability.
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Goal-directed action preparation in humans entails a mixture of corticospinal neural computations
The seemingly effortless ability of humans to transition from thinking about actions to initiating them relies on sculpting corticospinal output from primary motor cortex. This study tested whether canonical additive and multiplicative neural computations, well-described in sensory systems, generalize to the corticospinal pathway during human action preparation. We used non-invasive brain stimulation to measure corticospinal input-output across varying action preparation contexts during instructed-delay finger response tasks. Goal-directed action preparation was marked by increased multiplicative gain of corticospinal projections to task-relevant muscles and additive suppression of corticospinal projections to non-selected and task-irrelevant muscles. Individuals who modulated corticospinal gain to a greater extent were faster to initiate prepared responses. Our findings provide physiological evidence of combined additive suppression and gain modulation in the human motor system. We propose these computations support action preparation by enhancing the contrast between selected motor representations and surrounding background activity to facilitate response selection and execution.

Significance statementNeural computations determine what information is transmitted through brain circuits. We investigated whether the motor system uses computations similar to those observed in sensory systems by noninvasively stimulating the corticospinal pathway in humans during movement preparation. We discovered that corticospinal projections to behaviorally relevant muscles exhibit nonlinear gain computations, while projections to behaviorally irrelevant muscles exhibit linear suppression. Notably, individuals with stronger signatures of these computations had faster motor responses. Our findings suggest that certain computational principles generalize to the human motor system and serve to enhance the contrast between relevant and background neural activity.

VTA μ-opioidergic neurons facilitate low sociability in protracted opioid withdrawal
Opioids initiate dynamic maladaptation in brain reward and affect circuits that occur throughout chronic exposure and withdrawal that persist beyond cessation. Protracted withdrawal is characterized by negative affective behaviors such as heightened anxiety, irritability, dysphoria, and anhedonia, which pose a significant risk factor for relapse. While the ventral tegmental area (VTA) and mu-opioid recep-tors (MORs) are critical for opioid reinforcement, the specific contributions of VTA-MOR neurons in mediating protracted withdrawal-induced negative affect is not fully understood. In our study, we elucidate the role of VTA-MOR neurons in mediating negative affect and altered brain-wide neuronal activities following opioid exposure and withdrawal in male and female mice. Utilizing a chronic oral mor-phine administration model, we observe increased social deficit, anxiety-related, and despair-like behaviors during protracted with-drawal. VTA-MOR neurons show heightened neuronal FOS activation at the onset of withdrawal and connect to an array of brain regions that mediate reward and affective processes. Viral re-expression of MORs selectively within the VTA of MOR knockout mice demon-strates that the disrupted social interaction observed during protracted withdrawal is facilitated by this neural population, without affect-ing other protracted withdrawal behaviors. Lastly, VTA-MORs contribute to heightened neuronal FOS activation in the anterior cingulate cortex (ACC) in response to an acute morphine challenge, suggesting their unique role in modulating ACC-specific neuronal activity. These findings identify VTA-MOR neurons as critical modulators of low sociability during protracted withdrawal and highlight their potential as a mechanistic target to alleviate negative affective behaviors associated with opioid withdrawal.

Acute rapamycin treatment reveals novel mechanisms of behavioral, physiological, and functional dysfunction in a maternal inflammation mouse model of autism and sensory over-responsivity
Maternal inflammatory response (MIR) during early gestation in mice induces a cascade of physiological and behavioral changes that have been associated with autism spectrum disorder (ASD). In a prior study and the current one, we find that mild MIR results in chronic systemic and neuro-inflammation, mTOR pathway activation, mild brain overgrowth followed by regionally specific volumetric changes, sensory processing dysregulation, and social and repetitive behavior abnormalities. Prior studies of rapamycin treatment in autism models have focused on chronic treatments that might be expected to alter or prevent physical brain changes. Here, we have focused on the acute effects of rapamycin to uncover novel mechanisms of dysfunction and related to mTOR pathway signaling. We find that within 2 hours, rapamycin treatment could rapidly rescue neuronal hyper-excitability, seizure susceptibility, functional network connectivity and brain community structure, and repetitive behaviors and sensory over-responsivity in adult offspring with persistent brain overgrowth. These CNS-mediated effects are also associated with alteration of the expression of several ASD-,ion channel-, and epilepsy-associated genes, in the same time frame. Our findings suggest that mTOR dysregulation in MIR offspring is a key contributor to various levels of brain dysfunction, including neuronal excitability, altered gene expression in multiple cell types, sensory functional network connectivity, and modulation of information flow. However, we demonstrate that the adult MIR brain is also amenable to rapid normalization of these functional changes which results in the rescue of both core and comorbid ASD behaviors in adult animals without requiring long-term physical alterations to the brain. Thus, restoring excitatory/inhibitory imbalance and sensory functional network modularity may be important targets for therapeutically addressing both primary sensory and social behavior phenotypes, and compensatory repetitive behavior phenotypes.

A shared threat-anticipation circuit is dynamically engaged at different moments by certain and uncertain threat
Temporal dynamics play a central role in models of emotion: "fear" is widely conceptualized as a phasic response to certain-and-imminent danger, whereas "anxiety" is a sustained response to uncertain-or-distal harm. Yet the underlying human neurobiology remains contentious. Leveraging an ethnoracially diverse sample, translationally relevant paradigm, and theory-driven modeling approach, we demonstrate that certain and uncertain threat recruit a shared threat-anticipation circuit. This circuit exhibits persistently elevated activation when anticipating uncertain threat encounters and a transient burst of activation in the moments before certain encounters. For many scientists and clinicians, feelings are the defining feature of human fear and anxiety. Here we used an independently validated brain signature to covertly decode the momentary dynamics of anticipatory distress for the first time. Results mirrored the dynamics of neural activation. These observations provide fresh insights into the neurobiology of threat-elicited emotions and set the stage for more ambitious clinical and mechanistic research.

Brain Segregation and Integration Relate to Word-Finding Abilities in Older and Younger Adults
Previous research has shown that word-finding difficulties in older age are associated with functional and structural brain changes. However, the use of functional brain networks, measured through electroencephalography, to predict word-finding in older and younger adults has not yet been investigated. This study utilised resting-state electroencephalography data (61 channels) from the Leipzig Study for Mind-Body-Emotion Interactions dataset (Babayan et al., 2019) to investigate the relationship between functional brain networks and word-finding ability in healthy younger and older adults. Graph theory-based measures in individualised delta, theta, alpha, and beta bands were computed to assess brain segregation and integration of 53 older (aged 59-77) and 53 younger right-handed adults (aged 20-35). Word-finding ability was quantified as the number of orally produced words during a semantic and letter fluency task. Multiple linear regression revealed that, in older adults, greater functional connectedness in the delta band was associated with lower semantic fluency. Irrespective of age, greater modularity in the alpha band was related to lower semantic fluency. A greater small-world index in the delta band was related to better semantic fluency, irrespective of age. Increased brain integration in the delta band corresponded to greater semantic fluency in older adults. Hence, word-finding ability seems to be related to brain segregation and integration specific to the frequency band, possibly indicating alterations in cognitive control or compensatory shifts to less functionally specific frequency bands. The article further provides a discussion on neural dedifferentiation, hyper-synchronisation, study limitations, and directions for future research.

The replication principle revisited: a shared functional organization between pulvinar-cortical and cortico-cortical connectivity and its structural and molecular imaging correlates
The pulvinar, the largest nucleus in the human thalamus, is a complex, highly interconnected structure. Through a dense, organized network of cortical and subcortical areas, it provides adequate cooperation between neural systems, which is crucial for multiple high-order functions such as perception, visuospatial attention, and emotional processing. Such a central role is made possible by a precise internal topographical organization, which is mirrored by anatomical connections as well as by the expression of neurochemical markers. While being traditionally subdivided into sub-nuclei, each characterized by distinct connectional and morphological features, recent studies in both primate and human brains have highlighted that this topographical organization only marginally aligns with the conventional histological subdivision. Instead, it has been delineated in the context of continuous gradients of cortical connections along the dorsoventral and mediolateral axes. While this multi-gradient organization has been extensively documented in primate models, it remains relatively underexplored in the human brain. The present work combines high-quality, multi-modal structural and functional imaging data with a recently published whole-brain, large-scale, positron emission tomography (PET) atlas detailing 19 neurotransmitters and receptors distributed across the human brain. By applying diffusion embedding analysis to tractography, functional connectivity, and receptor coexpression data, we identify and characterize multiple topographically organized gradients of structural connections, functional coactivation, and molecular binding patterns. We demonstrate that such gradients converge on a shared representation along the dorsoventral and mediolateral axes of the human pulvinar. This representation aligns with transitions in both structural and functional connectivity, spanning from lower-level to higher-order cortical regions. Moreover, it is paralleled by gradual changes in the expression of molecular markers associated with key neuromodulator systems, including serotoninergic, noradrenergic, dopaminergic, and opioid systems. We contend that our findings mark a significant stride towards a more comprehensive understanding of pulvinar anatomy and function, providing a nuanced characterization of its role in health and disease.

Disentangling the Roles of Distinct Cell Classes with Cell-Type Dynamical Systems
Latent dynamical systems have been widely used to characterize the dynamics of neural population activity in the brain. However, these models typically ignore the fact that the brain contains multiple cell types. This limits their ability to capture the functional roles of distinct cell classes, or to accurately predict the effects of cell-specific optogenetic perturbations on neural activity or behavior. To overcome these limitations, we introduce the "cell-type dynamical systems" (CTDS) model. This model extends latent linear dynamical systems to contain distinct latent variables for each cell class, with biologically inspired constraints on both dynamics and emissions. To illustrate our approach, we consider neural recordings with distinct excitatory (E) and inhibitory (I) populations. The CTDS model defines separate latents for E and I cells, and constrains the dynamics so that E (I) latents have a strictly positive (negative) effects on other latents. We applied CTDS to recordings from rat frontal orienting fields (FOF) and anterior dorsal striatum (ADS) during an auditory decision-making task. The model achieved higher accuracy than a standard linear dynamical system (LDS), and revealed that both E and I latents could be used to decode the animal's choice, showing that choice-related information is not restricted to a single cell class. We also performed in-silico optogenetic perturbation experiments in the FOF and ADS, and found that CTDS was able to replicate the causal effects of different perturbations on behavior, whereas a standard LDS model which lacks the ability to capture cell-specific perturbations did not. Crucially, our model allowed us to understand the effects of these perturbations by revealing the dynamics of different cell-specific latents. Finally, CTDS can also be used to identify cell types for neurons whose class labels are unknown in electrophysiological recordings. These results illustrate the power of the CTDS model to provide more accurate and more biologically interpretable descriptions of neural population dynamics and their relationship to behavior.

Deep learning-driven neuromorphogenesis screenings identify repurposable drugs for mitochondrial disease
Mitochondrial disease encompasses untreatable conditions affecting tissues with high energy demands. A severe manifestation of mitochondrial disease is Leigh syndrome (Leigh), which causes defects in basal ganglia and midbrain regions, psychomotor regression, lactic acidosis, and early death. We previously generated isogenic pairs of Leigh cerebral organoids and uncovered defects in neuromorphogenesis. Here, we leveraged on this disease feature to devise drug discovery pipelines. We developed a deep learning algorithm tailored for cell type-specific drug repurposing to identify drugs capable of promoting neuronal commitment. In parallel, we performed a survival drug screen in yeast and validated the repurposable hits on branching capacity in Leigh neurons. The two approaches independently highlighted azole compounds, Talarozole and Sertaconazole, both of which lowered lactate release and improved neurogenesis and neurite organization in Leigh midbrain organoids. Hence, targeting neuromorphogenesis has led to identify potential new drugs for mitochondrial disease and could prove an effective strategy for further drug discovery.

Sleep induced by mechanosensory stimulation provides cognitive and health benefits in Drosophila
Study Objectives: Sleep is a complex phenomenon regulated by various factors, including sensory input. Anecdotal observations have suggested that gentle rocking helps babies fall asleep, and experimental studies have verified that rocking promotes sleep in both humans and mice. Recent studies have expanded this understanding, demonstrating that gentle vibration also induces sleep in Drosophila. Natural sleep serves multiple functions, including learning and memory, synaptic downscaling, and clearance of harmful substances associated with neurodegenerative diseases. Here, we investigated whether vibration-induced sleep provides similar cognitive and health benefits in Drosophila. Methods: We administered gentle vibration to flies that slept very little due to a forced activation of wake-promoting neurons and investigated how the vibration influenced learning and memory in the courtship conditioning paradigm. Additionally, we examined the effects of VIS on synaptic downscaling by counting synapse numbers of select neurons. Finally, we determined whether vibration could induce sleep in Drosophila models of Alzheimer's disease (AD) and promote the clearance of Amyloid {beta} (A{beta}) and Tubulin Associated Unit (TAU). Results: Vibration-induced sleep enhanced performance in a courtship conditioning paradigm and reduced the number of synapses in select neurons. Moreover, vibration improved sleep in Drosophila models of AD, promoting the clearance of A{beta} and TAU. Conclusions: Mechanosensory stimulation offers a promising non-invasive avenue for enhancing sleep, potentially providing associated cognitive and health benefits.

Oral cannabidiol administration in mice during pregnancy and lactation affects early postnatal body weight, fasting glucose, ingestive behavior, anxiety- and obsessive compulsive-like behaviors, and long-term object-memory in adult offspring in a sex-de
Rationale: The consequences of perinatal cannabidiol (CBD) exposure are severely understudied, but are important, given its widespread use and believed safety as a natural supplement. Objective: The objective of this study was to test the health, metabolic, and behavioral consequences of perinatal CBD exposure on dams and their offspring raised to adult. Methods: Primiparous female C57BL/6J mice were orally administered 100 mg/kg CBD in strawberry jam to expose offspring during gestation, lactation, or both using a cross-fostering design. Adult offspring were metabolically profiled using indirect calorimetry and intraperitoneal glucose tolerance testing. Adults were behaviorally phenotyped, video recorded, and mouse position tracked using DeepLabCut. Results: CBD was detected in maternal plasma using LC-MS 10-min post consumption (34.2 + 1.7 ng/ul) and peaked within 30 min (371.0 + 34.0 ng/ul). Fetal exposure to CBD significantly decreased survival of the pups, and decreased male postnatal development, but did not alter litter size, maternal body weight or pup birth weight. We observed many sex-dependent effects of perinatal CBD exposure. Exposure to CBD during gestation and lactation increased meal size, caloric intake, and respiratory exchange ratio for adult male offspring, while exposure during lactation decreased fasting glucose, but had no effect on clearance. Adult female offspring exposed to CBD during lactation showed increased drink size. Perinatal CBD exposure increased obsessive compulsive- and decreased anxiety-like behaviors (marble burying, light-dark box, elevated-plus maze) in female mice, decreased long-term object memory in male mice, and had no effect on attention tasks for either sex. Conclusions: We conclude that orally-administered CBD during pregnancy affects behavior and metabolism in a sex-dependent manner, and mice are differentially sensitive to exposure during gestation vs. lactation, or both. Because long-term changes are observed following perinatal exposure to the drug, and exposure significantly decreases survival to weaning, more research during development is warranted.

L-type calcium channel blockade with verapamil prevents noise induced neuronal dyssynchrony
Previous studies have established the protective effects of calcium channel blockade on the peripheral auditory system in response to noise exposure. While these studies implicate L-type calcium channels (LTCCs) in noise generated dysfunction in the auditory periphery, contributions of LTCCs to noise-induced central dysfunction remains unclear. To begin to elucidate the roles of LTCCs in hearing, peripheral and central auditory function were assessed longitudinally after LTCC blockade. Neuronal synchrony and activity were assessed by analyzing wave I (peripheral) and wave V (central) auditory brainstem responses (ABRs). Just prior to a noise exposure resulting in a temporary shift in hearing thresholds, rats were administered verapamil (LTCC blocker) or saline. Verapamil administration prevented the noise-induced decrease in ABR wave I and V amplitudes. Interestingly, when non-noise exposed animals were administered verapamil, wave V amplitude decreased, suggesting that LTCCs are critical for neuronal synchrony in the inferior colliculus. The inferior colliculus mediates inhibition of the acoustic startle reflex (giASR). Following noise exposure giASR was enhanced, but the enhancement was not prevented by LTCC blockade. These results suggest that while LTCCs are necessary for auditory-related synchronous activity, these channels do not contribute to noise-induced hyperactivity in the inferior colliculus.

Oxidative stress promotes axonal atrophy through alterations in microtubules and EB1 function
Axons are crucial for transmitting neurochemical signals. As organisms age, the ability of neurons to maintain their axons declines; hence aged axons are more susceptible to damage or dysfunction. Understanding what causes axonal vulnerability is crucial for developing strategies to enhance overall resilience of neurons, and to prevent their deterioration during ageing or in age-related neurodegenerative diseases. Increasing levels of reactive oxygen species (ROS) causes oxidative stress, a hallmark of ageing and age-related diseases. Despite this association, a causal relationship between oxidative stress and neuronal ageing remains unclear, particularly how subcellular physiology is affected by ROS. By using Drosophila-derived primary neuronal cultures and a recently developed in vivo neuronal model of ageing, which involves the visualisation of Drosophila medulla neurons, we investigated the interplay between oxidative stress, neuronal ageing and the microtubule cytoskeleton. We find that oxidative stress as a key driver of axonal and synaptic decay, including the appearance of axonal swellings, microtubule alterations in both axons and synapses and the morphological transformation of axonal terminals during ageing. We demonstrate that increased ROS sensitises the microtubule plus end binding factor, end-binding protein 1 (EB1), leading to microtubule defects, affecting neuronal integrity. Furthermore, manipulating EB1 proved to be a valuable therapeutic strategy to prevent ageing hallmarks observed in conditions of elevated ROS. In summary, we demonstrate a mechanistic pathway linking cellular oxidative stress, the microtubule cytoskeleton and axonal deterioration during ageing and provide evidence of the therapeutic potential of enhancing microtubule plus end physiology to improve the resilience of axons.

Translatome analysis reveals cellular network in DLK-dependent hippocampal glutamatergic neuron degeneration
The conserved MAP3K12/Dual Leucine Zipper Kinase (DLK) plays versatile roles in neuronal development, axon injury and stress responses, and neurodegeneration, depending on cell-type and cellular contexts. Emerging evidence implicates abnormal DLK signaling in several neurodegenerative diseases. However, our understanding of the DLK-dependent gene network in the central nervous system remains limited. Here, we investigated the roles of DLK in hippocampal glutamatergic neurons using conditional knockout and induced overexpression mice. We found that dorsal CA1 and dentate gyrus neurons are vulnerable to elevated expression of DLK, while CA3 neurons appear largely unaffected. We identified the DLK-dependent translatome that includes conserved molecular signatures and displays cell-type specificity. Increasing DLK signaling is associated with disruptions to microtubules, potentially involving STMN4. Additionally, primary cultured hippocampal neurons expressing different levels of DLK show altered neurite outgrowth, axon specification, and synapse formation. The identification of translational targets of DLK in hippocampal glutamatergic neurons has relevance to our understanding of neurodegenerative diseases.

Sarm1-Dependent Metabolic Reprogramming of Schwann Cells Following Nerve Injury
Schwann cells (SCs) transition into a repair phenotype after peripheral nerve injury, which is crucial for supporting axon regeneration. However, the early SC injury response preceding the repair state remains poorly understood. Here, we demonstrate that Sarm1, a key regulator of axon degeneration, is expressed in SCs and has a critical role in the early SC injury response. Leveraging the fact that Sarm1 deletion impairs the SC transition to the repair state, we used single-nucleus RNA sequencing to compare the transcriptional responses of wild-type and Sarm1 knockout SCs 24 hours after nerve injury. Remarkably, Sarm1-deficient SCs, unlike wild-type SCs, showed increased expression of genes involved in oxidative phosphorylation and the TCA cycle. These findings were functionally validated, revealing that Sarm1 knockout SCs displayed increased mitochondrial respiration in response to injury. Intriguingly, Sarm1 knockout SCs also exhibited enhanced axon protection compared to wild-type SCs in an in vitro model of axon degeneration. We propose that Sarm1 gates the transition of SCs from a protective, oxidative phosphorylation-dependent state (which we term Protection Associated Schwann Cells or PASCs) to a glycolytic, pro-regenerative repair phenotype after injury. Our findings challenge the prevailing view of Sarm1 as an exclusively axon-autonomous regulator of degeneration and reveal a paradigm shift in understanding the role of Sarm1 in the SC injury response, with broad implications for the treatment of peripheral neuropathies and neurodegenerative diseases.