Multisensory integration in the mouse striatum

A latent pool of neurons silenced by sensory-evoked inhibition can be recruited to enhance perception

To investigate which activity patterns in sensory cortex are relevant for perceptual decision-making, we combined two-photon calcium imaging and targeted two-photon optogenetics to interrogate barrel cortex activity during perceptual discrimination. We trained mice to discriminate bilateral whisker deflections and report decisions by licking left or right. Two-photon calcium imaging revealed sparse coding of contralateral and ipsilateral whisker input in layer 2/3, with most neurons remaining silent during the task. Activating pyramidal neurons using two-photon holographic photostimulation evoked a perceptual bias that scaled with the number of neurons photostimulated. This effect was dominated by optogenetic activation of non-coding neurons, which did not show sensory or motor-related activity during task performance. Photostimulation also revealed potent recruitment of cortical inhibition during sensory processing, which strongly and preferentially suppressed non-coding neurons. Our results suggest that a pool of non-coding neurons, selectively suppressed by network inhibition during sensory processing, can be recruited to enhance perception.

SHIELD: Skull-shaped hemispheric implants enabling large-scale electrophysiology datasets in the mouse brain

To understand the neural basis of behavior, it is essential to measure spiking dynamics across many interacting brain regions. Although new technologies, such as Neuropixels probes, facilitate multi-regional recordings, significant surgical and procedural hurdles remain for these experiments to achieve their full potential. Here, we describe skull-shaped hemispheric implants enabling large-scale electrophysiology datasets (SHIELD). These 3D-printed skull-replacement implants feature customizable insertion holes, allowing dozens of cortical and subcortical structures to be recorded in a single mouse using repeated multi-probe insertions over many days. We demonstrate the procedure's high success rate, biocompatibility, lack of adverse effects on behavior, and compatibility with imaging and optogenetics. To showcase SHIELD's scientific utility, we use multi-probe recordings to reveal novel insights into how alpha rhythms organize spiking activity across visual and sensorimotor networks. Overall, this method enables powerful, large-scale electrophysiological experiments for the study of distributed neural computation.

Beta-frequency sensory stimulation enhances gait rhythmicity through strengthened coupling between striatal networks and stepping movement

Stepping movement is delta (1-4 Hz) rhythmic and depends on sensory inputs. In addition to delta rhythms, beta (10-30 Hz) frequency dynamics are also prominent in the motor circuits and are coupled to neuronal delta rhythms both at the network and the cellular levels. Since beta rhythms are broadly supported by cortical and subcortical sensorimotor circuits, we explore how beta-frequency sensory stimulation influences delta-rhythmic stepping movement, and dorsal striatal circuit regulation of stepping. We delivered audiovisual stimulation at 10 Hz or 145 Hz to mice voluntarily locomoting, while simultaneously recording stepping movement, striatal cellular calcium dynamics and local field potentials (LFPs). We found that 10 Hz, but not 145 Hz stimulation prominently entrained striatal LFPs. Even though sensory stimulation at both frequencies promoted locomotion and desynchronized striatal network, only 10 Hz stimulation enhanced the delta rhythmicity of stepping movement and strengthened the coupling between stepping and striatal LFP delta and beta oscillations. These results demonstrate that higher frequency sensory stimulation can modulate lower frequency dorsal striatal neural dynamics and improve stepping rhythmicity, highlighting the translational potential of non-invasive beta-frequency sensory stimulation for improving gait.

Contributions of Basal Ganglia Circuits to Perception, Attention, and Consciousness

Research into ascending sensory pathways and cortical networks has generated detailed models of perception. These same cortical regions are strongly connected to subcortical structures, such as the basal ganglia (BG), which have been conceptualized as playing key roles in reinforcement learning and action selection. However, because the BG amasses experiential evidence from higher and lower levels of cortical hierarchies, as well as higher-order thalamus, it is well positioned to dynamically influence perception. Here, we review anatomical, functional, and clinical evidence to demonstrate how the BG can influence perceptual processing and conscious states. This depends on the integrative relationship between cortex, BG, and thalamus, which allows contributions to sensory gating, predictive processing, selective attention, and representation of the temporal structure of events.

Sensory-Behavioral Deficits in Parkinson's Disease: Insights from a 6-OHDA Mouse Model

Parkinson's disease (PD) is characterized by the degeneration of dopaminergic neurons in the striatum, predominantly associated with motor symptoms. However, non-motor deficits, particularly sensory symptoms, often precede motor manifestations, offering a potential early diagnostic window. The impact of non-motor deficits on sensation behavior and the underlying mechanisms remains poorly understood. In this study, we examined changes in tactile sensation within a Parkinsonian state by employing a mouse model of PD induced by 6-hydroxydopamine (6-OHDA) to deplete striatal dopamine (DA). Leveraging the conserved mouse whisker system as a model for tactile-sensory stimulation, we conducted psychophysical experiments to assess sensory-driven behavioral performance during a tactile detection task in both the healthy and Parkinson-like states. Our findings reveal that DA depletion induces pronounced alterations in tactile sensation behavior, extending beyond expected motor impairments. We observed diverse behavioral deficits, spanning detection performance, task engagement, and reward accumulation, among lesioned individuals. While subjects with extreme DA depletion consistently showed severe sensory behavioral deficits, others with substantial DA depletion displayed minimal changes in sensory behavior performance. Moreover, some exhibited moderate degradation of behavioral performance, likely stemming from sensory signaling loss rather than motor impairment. The implementation of a sensory detection task is a promising approach to quantify the extent of impairments associated with DA depletion in the animal model. This facilitates the exploration of early non-motor deficits in PD, emphasizing the importance of incorporating sensory assessments in understanding the diverse spectrum of PD symptoms.

Pathological cell assembly dynamics in a striatal MSN network model

Under normal conditions the principal cells of the striatum, medium spiny neurons (MSNs), show structured cell assembly activity patterns which alternate sequentially over exceedingly long timescales of many minutes. It is important to understand this activity since it is characteristically disrupted in multiple pathologies, such as Parkinson's disease and dyskinesia, and thought to be caused by alterations in the MSN to MSN lateral inhibitory connections and in the strength and distribution of cortical excitation to MSNs. To understand how these long timescales arise we extended a previous network model of MSN cells to include synapses with short-term plasticity, with parameters taken from a recent detailed striatal connectome study. We first confirmed the presence of sequentially switching cell clusters using the non-linear dimensionality reduction technique, Uniform Manifold Approximation and Projection (UMAP). We found that the network could generate non-stationary activity patterns varying extremely slowly on the order of minutes under biologically realistic conditions. Next we used Simulation Based Inference (SBI) to train a deep net to map features of the MSN network generated cell assembly activity to MSN network parameters. We used the trained SBI model to estimate MSN network parameters from ex-vivo brain slice calcium imaging data. We found that best fit network parameters were very close to their physiologically observed values. On the other hand network parameters estimated from Parkinsonian, decorticated and dyskinetic ex-vivo slice preparations were different. Our work may provide a pipeline for diagnosis of basal ganglia pathology from spiking data as well as for the design pharmacological treatments.

Cell-type specific auditory responses in the striatum are shaped by feed forward inhibition

The posterior "tail" region of the striatum receives dense innervation from sensory brain regions and has been demonstrated to play a role in behaviors that require sensorimotor integration including discrimination 1,2 , avoidance 3 and defense 4 responses. The output neurons of the striatum, the D1 and D2 striatal projection neurons (SPNs) that make up the direct and indirect pathways, respectively, are thought to play differential roles in these behavioral responses, although it remains unclear if or how these neurons display differential responsivity to sensory stimuli. Here, we used whole-cell recordings in vivo and ex vivo to examine the strength of excitatory and inhibitory synaptic inputs onto D1 and D2 SPNs following the stimulation of upstream auditory pathways. While D1 and D2 SPNs both displayed stimulus-evoked depolarizations, D1 SPN responses were stronger and faster for all stimuli tested in vivo as well as in brain slices. This difference did not arise from differences in the strength of excitatory inputs but from differences in the strength of feed forward inhibition. Indeed, fast spiking interneurons, which are readily engaged by auditory afferents exerted stronger inhibition onto D2 SPNs compared to D1 SPNs. Our results support a model in which differences in feed forward inhibition enable the preferential recruitment of the direct pathway in response to auditory stimuli, positioning this pathway to initiate sound-driven actions.

Anti-Hebbian plasticity drives sequence learning in striatum

Spatio-temporal activity patterns have been observed in a variety of brain areas in spontaneous activity, prior to or during action, or in response to stimuli. Biological mechanisms endowing neurons with the ability to distinguish between different sequences remain largely unknown. Learning sequences of spikes raises multiple challenges, such as maintaining in memory spike history and discriminating partially overlapping sequences. Here, we show that anti-Hebbian spike-timing dependent plasticity (STDP), as observed at cortico-striatal synapses, can naturally lead to learning spike sequences. We design a spiking model of the striatal output neuron receiving spike patterns defined as sequential input from a fixed set of cortical neurons. We use a simple synaptic plasticity rule that combines anti-Hebbian STDP and non-associative potentiation for a subset of the presented patterns called rewarded patterns. We study the ability of striatal output neurons to discriminate rewarded from non-rewarded patterns by firing only after the presentation of a rewarded pattern. In particular, we show that two biological properties of striatal networks, spiking latency and collateral inhibition, contribute to an increase in accuracy, by allowing a better discrimination of partially overlapping sequences. These results suggest that anti-Hebbian STDP may serve as a biological substrate for learning sequences of spikes.

Role of Posterior Medial Thalamus in the Modulation of Striatal Circuitry and Choice Behavior

The posterior medial (POm) thalamus is heavily interconnected with sensory and motor circuitry and is likely involved in behavioral modulation and sensorimotor integration. POm provides axonal projections to the dorsal striatum, a hotspot of sensorimotor processing, yet the role of POm-striatal projections has remained undetermined. Using optogenetics with slice electrophysiology, we found that POm provides robust synaptic input to direct and indirect pathway striatal spiny projection neurons (D1- and D2-SPNs, respectively) and parvalbumin-expressing fast spiking interneurons (PVs). During the performance of a whisker-based tactile discrimination task, POm-striatal projections displayed learning-related activation correlating with anticipatory, but not reward-related, pupil dilation. Inhibition of POm-striatal axons across learning caused slower reaction times and an increase in the number of training sessions for expert performance. Our data indicate that POm-striatal inputs provide a behaviorally relevant arousal-related signal, which may prime striatal circuitry for efficient integration of subsequent choice-related inputs.

The Interactions of Temporal and Sensory Representations in the Basal Ganglia

In rodents and primates, interval estimation has been associated with a complex network of cortical and subcortical structures where the dorsal striatum plays a paramount role. Diverse evidence ranging from individual neurons to population activity has demonstrated that this area hosts temporal-related neural representations that may be instrumental for the perception and production of time intervals. However, little is known about how temporal representations interact with other well-known striatal representations, such as kinematic parameters of movements or somatosensory representations. An attractive hypothesis suggests that somatosensory representations may serve as the scaffold for complex representations such as elapsed time. Alternatively, these representations may coexist as independent streams of information that could be integrated into downstream nuclei, such as the substantia nigra or the globus pallidus. In this review, we will revise the available information suggesting an instrumental role of sensory representations in the construction of temporal representations at population and single-neuron levels throughout the basal ganglia.

GABAergic regulation of striatal spiny projection neurons depends upon their activity state

Synaptic transmission mediated by GABAA receptors (GABAARs) in adult, principal striatal spiny projection neurons (SPNs) can suppress ongoing spiking, but its effect on synaptic integration at subthreshold membrane potentials is less well characterized, particularly those near the resting down-state. To fill this gap, a combination of molecular, optogenetic, optical, and electrophysiological approaches were used to study SPNs in mouse ex vivo brain slices, and computational tools were used to model somatodendritic synaptic integration. In perforated patch recordings, activation of GABAARs, either by uncaging of GABA or by optogenetic stimulation of GABAergic synapses, evoked currents with a reversal potential near -60 mV in both juvenile and adult SPNs. Transcriptomic analysis and pharmacological work suggested that this relatively positive GABAAR reversal potential was not attributable to NKCC1 expression, but rather to HCO3- permeability. Regardless, from down-state potentials, optogenetic activation of dendritic GABAergic synapses depolarized SPNs. This GABAAR-mediated depolarization summed with trailing ionotropic glutamate receptor (iGluR) stimulation, promoting dendritic spikes and increasing somatic depolarization. Simulations revealed that a diffuse dendritic GABAergic input to SPNs effectively enhanced the response to dendritic iGluR signaling and promoted dendritic spikes. Taken together, our results demonstrate that GABAARs can work in concert with iGluRs to excite adult SPNs when they are in the resting down-state, suggesting that their inhibitory role is limited to brief periods near spike threshold. This state-dependence calls for a reformulation for the role of intrastriatal GABAergic circuits.

Multisensory Integration and Causal Inference in Typical and Atypical Populations

Multisensory perception is critical for effective interaction with the environment, but human responses to multisensory stimuli vary across the lifespan and appear changed in some atypical populations. In this review chapter, we consider multisensory integration within a normative Bayesian framework. We begin by outlining the complex computational challenges of multisensory causal inference and reliability-weighted cue integration, and discuss whether healthy young adults behave in accordance with normative Bayesian models. We then compare their behaviour with various other human populations (children, older adults, and those with neurological or neuropsychiatric disorders). In particular, we consider whether the differences seen in these groups are due only to changes in their computational parameters (such as sensory noise or perceptual priors), or whether the fundamental computational principles (such as reliability weighting) underlying multisensory perception may also be altered. We conclude by arguing that future research should aim explicitly to differentiate between these possibilities.

From Multisensory Integration to Multisensory Decision-Making

Organisms live in a dynamic environment in which sensory information from multiple sources is ever changing. A conceptually complex task for the organisms is to accumulate evidence across sensory modalities and over time, a process known as multisensory decision-making. This is a new concept, in terms of that previous researches have been largely conducted in parallel disciplines. That is, much efforts have been put either in sensory integration across modalities using activity summed over a duration of time, or in decision-making with only one sensory modality that evolves over time. Recently, a few studies with neurophysiological measurements emerge to study how different sensory modality information is processed, accumulated, and integrated over time in decision-related areas such as the parietal or frontal lobes in mammals. In this review, we summarize and comment on these studies that combine the long-existed two parallel fields of multisensory integration and decision-making. We show how the new findings provide insight into our understanding about neural mechanisms mediating multisensory information processing in a more complete way.

Pathways from the Superior Colliculus to the Basal Ganglia

The present work aims to review the structural organization of the mammalian superior colliculus (SC), the putative pathways connecting the SC and the basal ganglia, and their role in organizing complex behavioral output. First, we review how the complex intrinsic connections between the SC's laminae projections allow for the construction of spatially aligned, visual-multisensory maps of the surrounding environment. Moreover, we present a summary of the sensory-motor inputs of the SC, including a description of the integration of multi-sensory inputs relevant to behavioral control. We further examine the major descending outputs toward the brainstem and spinal cord. As the central piece of this review, we provide a thorough analysis covering the putative interactions between the SC and the basal ganglia. To this end, we explore the diverse thalamic routes by which information from the SC may reach the striatum, including the pathways through the lateral posterior, parafascicular, and rostral intralaminar thalamic nuclei. We also examine the interactions between the SC and subthalamic nucleus, representing an additional pathway for the tectal modulation of the basal ganglia. Moreover, we discuss how information from the SC might also be relayed to the basal ganglia through midbrain tectonigral and tectotegmental projections directed at the substantia nigra compacta and ventrotegmental area, respectively, influencing the dopaminergic outflow to the dorsal and ventral striatum. We highlight the vast interplay between the SC and the basal ganglia and raise several missing points that warrant being addressed in future studies.

Magnetogenetic stimulation inside MRI induces spontaneous and evoked changes in neural circuits activity in rats

The ability to modulate specific neural circuits and simultaneously visualize and measure brain activity with MRI would greatly impact understanding brain function in health and disease. The combination of neurostimulation methods and MRI in animal models have already shown promise in elucidating fundamental mechanisms associated with brain activity. We developed an innovative magnetogenetics neurostimulation technology that can trigger neural activity through magnetic fields. Similar to other genetic-based neuromodulation methods, magnetogenetics offers cell-, area- and temporal-specific control of neural activity. However, the magnetogenetics protein (Electromagnetic Preceptive Gene (EPG)) are activated by non-invasive magnetic fields, providing a unique way to target neural circuits by the MRI gradients while simultaneously measure their effect on brain activity. EPG was expressed in rat's visual cortex and the amplitude of low-frequency fluctuation (fALFF), resting-state functional connectivity (FC), and sensory activation was measured using a 7T MRI. The results demonstrate that EPG-expressing rats had significantly higher signal fluctuations in the visual areas and stronger FC in sensory areas consistent with known anatomical visuosensory and visuomotor connections. This new technology complements the existing neurostimulation toolbox and provides a mean to study brain function in a minimally-invasive way which was not possible previously.

Callosal inputs generate side-invariant receptive fields in the barrel cortex

Barrel cortex integrates contra- and ipsilateral whiskers' inputs. While contralateral inputs depend on the thalamocortical innervation, ipsilateral ones are thought to rely on callosal axons. These are more abundant in the barrel cortex region bordering with S2 and containing the row A-whiskers representation, the row lying nearest to the facial midline. Here, we ask what role this callosal axonal arrangement plays in ipsilateral tactile signaling. We found that novel object exploration with ipsilateral whiskers confines c-Fos expression within the highly callosal subregion. Targeting this area with in vivo patch-clamp recordings revealed neurons with uniquely strong ipsilateral responses dependent on the corpus callosum, as assessed by tetrodotoxin silencing and by optogenetic activation of the contralateral hemisphere. Still, in this area, stimulation of contra- or ipsilateral row A-whiskers evoked an indistinguishable response in some neurons, mostly located in layers 5/6, indicating their involvement in the midline representation of the whiskers' sensory space.

Corticostriatal pathways for bilateral sensorimotor functions

Corticostriatal pathways are essential for a multitude of motor, sensory, cognitive, and affective functions. They are mediated by cortical pyramidal neurons, roughly divided into two projection classes: the pyramidal tract (PT) and the intratelencephalic tract (IT). These pathways have been the focus of numerous studies in recent years, revealing their distinct structural and functional properties. Notably, their synaptic connectivity within ipsi- and contralateral cortical and striatal microcircuits is characterized by a high degree of target selectivity, providing a means to regulate the local neuromodulatory landscape in the striatum. Here, we discuss recent findings regarding the functional organization of the PT and IT corticostriatal pathways and its implications for bilateral sensorimotor functions.

Distinct Patterns of Connectivity between Brain Regions Underlie the Intra-Modal and Cross-Modal Value-Driven Modulations of the Visual Cortex

Past reward associations may be signaled from different sensory modalities; however, it remains unclear how different types of reward-associated stimuli modulate sensory perception. In this human fMRI study (female and male participants), a visual target was simultaneously presented with either an intra- (visual) or a cross-modal (auditory) cue that was previously associated with rewards. We hypothesized that, depending on the sensory modality of the cues, distinct neural mechanisms underlie the value-driven modulation of visual processing. Using a multivariate approach, we confirmed that reward-associated cues enhanced the target representation in early visual areas and identified the brain valuation regions. Then, using an effective connectivity analysis, we tested three possible patterns of connectivity that could underlie the modulation of the visual cortex: a direct pathway from the frontal valuation areas to the visual areas, a mediated pathway through the attention-related areas, and a mediated pathway that additionally involved sensory association areas. We found evidence for the third model demonstrating that the reward-related information in both sensory modalities is communicated across the valuation and attention-related brain regions. Additionally, the superior temporal areas were recruited when reward was cued cross-modally. The strongest dissociation between the intra- and cross-modal reward-driven effects was observed at the level of the feedforward and feedback connections of the visual cortex estimated from the winning model. These results suggest that, in the presence of previously rewarded stimuli from different sensory modalities, a combination of domain-general and domain-specific mechanisms are recruited across the brain to adjust the visual perception.SIGNIFICANCE STATEMENT Reward has a profound effect on perception, but it is not known whether shared or disparate mechanisms underlie the reward-driven effects across sensory modalities. In this human fMRI study, we examined the reward-driven modulation of the visual cortex by visual (intra-modal) and auditory (cross-modal) reward-associated cues. Using a model-based approach to identify the most plausible pattern of inter-regional effective connectivity, we found that higher-order areas involved in the valuation and attentional processing were recruited by both types of rewards. However, the pattern of connectivity between these areas and the early visual cortex was distinct between the intra- and cross-modal rewards. This evidence suggests that, to effectively adapt to the environment, reward signals may recruit both domain-general and domain-specific mechanisms.

Striatal Dopamine Signals and Reward Learning

We are constantly bombarded by sensory information and constantly making decisions on how to act. In order to optimally adapt behavior, we must judge which sequences of sensory inputs and actions lead to successful outcomes in specific circumstances. Neuronal circuits of the basal ganglia have been strongly implicated in action selection, as well as the learning and execution of goal-directed behaviors, with accumulating evidence supporting the hypothesis that midbrain dopamine neurons might encode a reward signal useful for learning. Here, we review evidence suggesting that midbrain dopaminergic neurons signal reward prediction error, driving synaptic plasticity in the striatum underlying learning. We focus on phasic increases in action potential firing of midbrain dopamine neurons in response to unexpected rewards. These dopamine neurons prominently innervate the dorsal and ventral striatum. In the striatum, the released dopamine binds to dopamine receptors, where it regulates the plasticity of glutamatergic synapses. The increase of striatal dopamine accompanying an unexpected reward activates dopamine type 1 receptors (D1Rs) initiating a signaling cascade that promotes long-term potentiation of recently active glutamatergic input onto striatonigral neurons. Sensorimotor-evoked glutamatergic input, which is active immediately before reward delivery will thus be strengthened onto neurons in the striatum expressing D1Rs. In turn, these neurons cause disinhibition of brainstem motor centers and disinhibition of the motor thalamus, thus promoting motor output to reinforce rewarded stimulus-action outcomes. Although many details of the hypothesis need further investigation, altogether, it seems likely that dopamine signals in the striatum might underlie important aspects of goal-directed reward-based learning.

An Open-Field-Based Unimodal Object Recognition Test (OF-UORT) for Assessment of Chronic Stress Effects on Visual and Tactile Unimodal Cognition in Mice

The open field (OF) test is a widely used behavioral assay in animal studies to assess locomotion, emotion, and cognition. In open-field-based object recognition tasks, the open arena is equipped with combinations of objects to allow the examination of various aspects of learning and memory. In this article, we provide a protocol for open-field-based unimodal memory tests that assess tactile or visual unimodal cognitive behavior in mice. These tests do not require mice to be restricted from eating or drinking and do not involve aversive stimuli, such as electric shock, high-decibel sound waves, bright light, or forced swimming. Inside the apparatus, mice can freely and spontaneously explore the objects and the environment. Sniffing of, or direct contact with, objects is considered a cognitive exploration of the objects, and the timing and number of such behaviors can be recorded. During the acquisition phase, two identical objects are provided. After an intertrial interval, the retrieval phase is initiated, during which one object is replaced with a new object that is different from the previous one. Decorative clear domes are used prevent direct tactile contact with the objects, whereas infrared illumination is used to block visual information from the objects. By alternating the access to visual or tactile features of the objects in the acquisition and retrieval phases, the experimenters can assess visual or tactile unimodal cognition. Here, we describe our own instrumentation and application for experiments, and demonstrate that the modified device is capable of testing visual or tactile unimodal cognition in mice. Although easy to perform, this task/test can accurately reflect unimodal cognitive performance in mice, which can provide solid and reproducible data support to related studies. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Validation of the open-field-based unimodal object recognition test Basic Protocol 2: Evaluation of chronic stress effects on unimodal cognition using the open-field-based unimodal cognitive test.

The respective activation and silencing of striatal direct and indirect pathway neurons support behavior encoding

The basal ganglia are known to control actions and modulate movements. Neuronal activity in the two efferent pathways of the dorsal striatum is critical for appropriate behavioral control. Previous evidence has led to divergent conclusions on the respective engagement of both pathways during actions. Using calcium imaging to evaluate how neurons in the direct and indirect pathways encode behaviors during self-paced spontaneous explorations in an open field, we observed that the two striatal pathways exhibit distinct tuning properties. Supervised learning algorithms revealed that direct pathway neurons encode behaviors through their activation, whereas indirect pathway neurons exhibit behavior-specific silencing. These properties remain stable for weeks. Our findings highlight a complementary encoding of behaviors with congruent activations in the direct pathway encoding multiple accessible behaviors in a given context, and in the indirect pathway encoding the suppression of competing behaviors. This model reconciles previous conflicting conclusions on motor encoding in the striatum.

Anterior cingulate glutamate levels associate with functional activation and connectivity during sensory integration in schizophrenia: a multimodal 1H-MRS and fMRI study

BACKGROUND

Glutamatergic dysfunction has been implicated in sensory integration deficits in schizophrenia, yet how glutamatergic function contributes to behavioural impairments and neural activities of sensory integration remains unknown.

METHODS

Fifty schizophrenia patients and 43 healthy controls completed behavioural assessments for sensory integration and underwent magnetic resonance spectroscopy (MRS) for measuring the anterior cingulate cortex (ACC) glutamate levels. The correlation between glutamate levels and behavioural sensory integration deficits was examined in each group. A subsample of 20 pairs of patients and controls further completed an audiovisual sensory integration functional magnetic resonance imaging (fMRI) task. Blood Oxygenation Level Dependent (BOLD) activation and task-dependent functional connectivity (FC) were assessed based on fMRI data. Full factorial analyses were performed to examine the Group-by-Glutamate Level interaction effects on fMRI measurements (group differences in correlation between glutamate levels and fMRI measurements) and the correlation between glutamate levels and fMRI measurements within each group.

RESULTS

We found that schizophrenia patients exhibited impaired sensory integration which was positively correlated with ACC glutamate levels. Multimodal analyses showed significantly Group-by-Glutamate Level interaction effects on BOLD activation as well as task-dependent FC in a 'cortico-subcortical-cortical' network (including medial frontal gyrus, precuneus, ACC, middle cingulate gyrus, thalamus and caudate) with positive correlations in patients and negative in controls.

CONCLUSIONS

Our findings indicate that ACC glutamate influences neural activities in a large-scale network during sensory integration, but the effects have opposite directionality between schizophrenia patients and healthy people. This implicates the crucial role of glutamatergic system in sensory integration processing in schizophrenia.

MAM-2201 acute administration impairs motor, sensorimotor, prepulse inhibition, and memory functions in mice: a comparison with its analogue AM-2201

RATIONALE

1-[(5-fluoropentyl)-1H-indol-3-yl](4-methyl-1-naphthalenyl) methanone (MAM-2201) is a potent synthetic cannabinoid receptor agonist illegally marketed in "spice" products and as "synthacaine" for its psychoactive effects. It is a naphthoyl-indole derivative which differs from its analogue 1-[(5-Fluoropentyl)-1H-indol-3-yl](1-naphthylenyl) methanone (AM-2201) by the presence of a methyl substituent on carbon 4 (C-4) of the naphthoyl moiety. Multiple cases of intoxication and impaired driving have been linked to AM-2201 and MAM-2201 consumption.

OBJECTIVES

This study aims to investigate the in vitro (murine and human cannabinoid receptors) and in vivo (CD-1 male mice) pharmacodynamic activity of MAM-2201 and compare its effects with those induced by its desmethylated analogue, AM-2201.

RESULTS

In vitro competition binding studies confirmed that MAM-2201 and AM-2201 possess nanomolar affinity for both CD-1 murine and human CB₁ and CB₂ receptors, with preference for the CB₁ receptor. In agreement with the in vitro binding data, in vivo studies showed that MAM-2201 induces visual, acoustic, and tactile impairments that were fully prevented by pretreatment with CB₁ receptor antagonist/partial agonist AM-251, indicating a CB₁ receptor mediated mechanism of action. Administration of MAM-2201 also altered locomotor activity and PPI responses of mice, pointing out its detrimental effect on motor and sensory gating functions and confirming its potential use liability. MAM-2201 and AM-2201 also caused deficits in short- and long-term working memory.

CONCLUSION

These findings point to the potential public health burden that these synthetic cannabinoids may pose, with particular emphasis on impaired driving and workplace performance.

Ethanol enhances JWH-018-induced impairment of sensorimotor and memory functions in mice: From preclinical evidence to forensic implication in Driving Under the Influence of Drugs

BACKGROUND

Several new Synthetic Cannabinoids have appeared each year since their introduction into the illicit drug market as recreational drugs. Among these, naphtalen-1-yl-(1-pentylindol-3-yl) methanone (JWH-018) is one of the most detected compounds in biological samples from patients involved in intoxication or death cases. Furthermore, consumption of JWH-018 has been linked to several cases of Driving Under the Influence of Drugs (DUID) suggesting that effects induced by this compound can affect individuals' ability to drive.

METHODS

Given the high spread of polydrug consumption and the wide number of alcohol-related traffic accidents, this study aims to investigate the acute effects induced by co-administration of JWH-018 with ethanol on sensorimotor and motor responses, grip strength and memory functions in CD-1 male mice. Acute impairments induced by JWH-018 and ethanol alone have also been investigated, in order to compare their effects with that induced by their concurrent administration.

RESULTS

In vivo behavioral experiments revealed a worsening of the cognitive and sensorimotor disruption after the co-administration of JWH-018 with ethanol compared to single compounds.

CONCLUSIONS

These animal-based findings suggest a potential increased impairment on psychomotor performances which could be related to driving abilities posed by poly-drug consumption involving SCs and ethanol.

State-dependent GABAergic regulation of striatal spiny projection neuron excitability

Synaptic transmission mediated by GABA A receptors (GABA A Rs) in adult, principal striatal spiny projection neurons (SPNs) can suppress ongoing spiking, but its effect on synaptic integration at sub-threshold membrane potentials is less well characterized, particularly those near the resting down-state. To fill this gap, a combination of molecular, optogenetic, optical and electrophysiological approaches were used to study SPNs in mouse ex vivo brain slices, and computational tools were used to model somatodendritic synaptic integration. Activation of GABA A Rs, either by uncaging of GABA or by optogenetic stimulation of GABAergic synapses, evoked currents with a reversal potential near -60 mV in perforated patch recordings from both juvenile and adult SPNs. Molecular profiling of SPNs suggested that this relatively positive reversal potential was not attributable to NKCC1 expression, but rather to a dynamic equilibrium between KCC2 and Cl-/HCO3-cotransporters. Regardless, from down-state potentials, optogenetic activation of dendritic GABAergic synapses depolarized SPNs. This GABAAR-mediated depolarization summed with trailing ionotropic glutamate receptor (iGluR) stimulation, promoting dendritic spikes and increasing somatic depolarization. Simulations revealed that a diffuse dendritic GABAergic input to SPNs effectively enhanced the response to coincident glutamatergic input. Taken together, our results demonstrate that GABA A Rs can work in concert with iGluRs to excite adult SPNs when they are in the resting down-state, suggesting that their inhibitory role is limited to brief periods near spike threshold. This state-dependence calls for a reformulation of the role intrastriatal GABAergic circuits.

Ongoing movement controls sensory integration in the dorsolateral striatum

The dorsolateral striatum (DLS) receives excitatory inputs from both sensory and motor cortical regions. In the neocortex, sensory responses are affected by motor activity, however, it is not known whether such sensorimotor interactions occur in the striatum and how they are shaped by dopamine. To determine the impact of motor activity on striatal sensory processing, we performed in vivo whole-cell recordings in the DLS of awake mice during the presentation of tactile stimuli. Striatal medium spiny neurons (MSNs) were activated by both whisker stimulation and spontaneous whisking, however, their responses to whisker deflection during ongoing whisking were attenuated. Dopamine depletion reduced the representation of whisking in direct-pathway MSNs, but not in those of the indirect-pathway. Furthermore, dopamine depletion impaired the discrimination between ipsilateral and contralateral sensory stimulation in both direct and indirect pathway MSNs. Our results show that whisking affects sensory responses in DLS and that striatal representation of both processes is dopamine- and cell type-dependent.

Sensory processing in external globus pallidus neurons

Sensory processing is crucial for execution of appropriate behavior. The external globus pallidus (GPe), a nucleus within the basal ganglia, is highly involved in the control of movement and could potentially integrate sensory-motor information. The GPe comprises prototypic and arkypallidal cells, which receive partially overlapping inputs. It is unclear, however, which inputs convey sensory information to them. Here, we used in vivo whole-cell recordings in the mouse GPe and optogenetic silencing to characterize the pathways that shape the response to whisker stimulation in prototypic and arkypallidal cells. Our results show that sensory integration in prototypic cells is controlled by the subthalamic nucleus and indirect pathway medium spiny neurons (MSNs), whereas in arkypallidal cells, it is primarily shaped by direct pathway MSNs. These results suggest that GPe subpopulations receive sensory information from largely different neural populations, reinforcing that the GPe consists of two parallel pathways, which differ anatomically and functionally.

Chronic multiscale resolution of mouse brain networks using combined mesoscale cortical imaging and subcortical fiber photometry

SIGNIFICANCE

Genetically encoded optical probes to image calcium levels in neurons in vivo are used widely as a real-time measure of neuronal activity in the brain. Mesoscale calcium imaging through a cranial window provides a method of studying the interaction of circuit activity between cortical areas but lacks access to subcortical regions.

AIM

We have developed an optical and surgical preparation that preserves wide-field imaging of the cortical surface while also permitting access to specific subcortical networks.

APPROACH

This was achieved using an optical fiber implanted in the striatum, along with a bilateral widefield cranial window, enabling simultaneous mesoscale cortical imaging and subcortical fiber photometry recording of calcium signals in a transgenic animal expressing GCaMP. Subcortical signals were collected from the dorsal regions of the striatum. We combined this approach with multiple sensory-motor tasks, including specific auditory and visual stimulation, and video monitoring of animal movements and pupillometry during head-fixed behaviors.

RESULTS

We found high correlations between cortical and striatal activity in response to sensory stimulation or movement. Furthermore, spontaneous activity recordings revealed that specific motifs of cortical activity are correlated with presynaptic activity recorded in the striatum, enabling us to select for corticostriatal activity motifs.

CONCLUSION

We believe that this method can be utilized to reveal not only global patterns but also cell-specific connectivity that provides insight into corticobasal ganglia circuit organization.

Cilia in the Striatum Mediate Timing-Dependent Functions

Almost all brain cells contain cilia, antennae-like microtubule-based organelles. Yet, the significance of cilia, once considered vestigial organelles, in the higher-order brain functions is unknown. Cilia act as a hub that senses and transduces environmental sensory stimuli to generate an appropriate cellular response. Similarly, the striatum, a brain structure enriched in cilia, functions as a hub that receives and integrates various types of environmental information to drive appropriate motor response. To understand cilia's role in the striatum functions, we used loxP/Cre technology to ablate cilia from the dorsal striatum of male mice and monitored the behavioral consequences. Our results revealed an essential role for striatal cilia in the acquisition and brief storage of information, including learning new motor skills, but not in long-term consolidation of information or maintaining habitual/learned motor skills. A fundamental aspect of all disrupted functions was the "time perception/judgment deficit." Furthermore, the observed behavioral deficits form a cluster pertaining to clinical manifestations overlapping across psychiatric disorders that involve the striatum functions and are known to exhibit timing deficits. Thus, striatal cilia may act as a calibrator of the timing functions of the basal ganglia-cortical circuit by maintaining proper timing perception. Our findings suggest that dysfunctional cilia may contribute to the pathophysiology of neuro-psychiatric disorders, as related to deficits in timing perception.

Multisensory stimuli enhance the effectiveness of equivalence learning in healthy children and adolescents

It has been demonstrated earlier in healthy adult volunteers that visually and multisensory (audiovisual) guided equivalence learning are similarly effective. Thus, these processes seem to be independent of stimulus modality. The question arises as to whether this phenomenon can be observed also healthy children and adolescents. To assess this, visual and audiovisual equivalence learning was tested in 157 healthy participants younger than 18 years of age, in both a visual and an audiovisual paradigm consisting of acquisition, retrieval and generalization phases. Performance during the acquisition phase (building of associations), was significantly better in the multisensory paradigm, but there was no difference between the reaction times (RTs). Performance during the retrieval phase (where the previously learned associations are tested) was also significantly better in the multisensory paradigm, and RTs were significantly shorter. On the other hand, transfer (generalization) performance (where hitherto not learned but predictable associations are tested) was not significantly enhanced in the multisensory paradigm, while RTs were somewhat shorter. Linear regression analysis revealed that all the studied psychophysical parameters in both paradigms showed significant correlation with the age of the participants. Audiovisual stimulation enhanced acquisition and retrieval as compared to visual stimulation only, regardless of whether the subjects were above or below 12 years of age. Our results demonstrate that multisensory stimuli significantly enhance association learning and retrieval in the context of sensory guided equivalence learning in healthy children and adolescents. However, the audiovisual gain was significantly higher in the cohort below 12 years of age, which suggests that audiovisually guided equivalence learning is still in development in childhood.

In Vivo Bio-Activation of JWH-175 to JWH-018: Pharmacodynamic and Pharmacokinetic Studies in Mice

3-(1-Naphthalenylmethyl)-1-pentyl-1H-indole (JWH-175) is a synthetic cannabinoid illegally marketed for its psychoactive cannabis-like effects. This study aimed to investigate and compare in vitro and in vivo pharmacodynamic activity of JWH-175 with that of 1-naphthalenyl (1-pentyl-1H-indol-3-yl)-methanone (JWH-018), as well as evaluate the in vitro (human liver microsomes) and in vivo (urine and plasma of CD-1 male mice) metabolic profile of JWH-175. In vitro binding studies showed that JWH-175 is a cannabinoid receptor agonist less potent than JWH-018 on mouse and human CB1 and CB2 receptors. In agreement with in vitro data, JWH-175 reduced the fESPS in brain hippocampal slices of mice less effectively than JWH-018. Similarly, in vivo behavioral studies showed that JWH-175 impaired sensorimotor responses, reduced breath rate and motor activity, and increased pain threshold to mechanical stimuli less potently than JWH-018. Metabolic studies demonstrated that JWH-175 is rapidly bioactivated to JWH-018 in mice blood, suggesting that in vivo effects of JWH-175 are also due to JWH-018 formation. The pharmaco-toxicological profile of JWH-175 was characterized for the first time, proving its in vivo bio-activation to the more potent agonist JWH-018. Thus, it highlighted the great importance of investigating the in vivo metabolism of synthetic cannabinoids for both clinical toxicology and forensic purposes.

Non-uniform distribution of dendritic nonlinearities differentially engages thalamostriatal and corticostriatal inputs onto cholinergic interneurons

The tonic activity of striatal cholinergic interneurons (CINs) is modified differentially by their afferent inputs. Although their unitary synaptic currents are identical, in most CINs cortical inputs onto distal dendrites only weakly entrain them, whereas proximal thalamic inputs trigger abrupt pauses in discharge in response to salient external stimuli. To test whether the dendritic expression of the active conductances that drive autonomous discharge contribute to the CINs’ capacity to dissociate cortical from thalamic inputs, we used an optogenetics-based method to quantify dendritic excitability in mouse CINs. We found that the persistent sodium (NaP) current gave rise to dendritic boosting, and that the hyperpolarization-activated cyclic nucleotide-gated (HCN) current gave rise to a subhertz membrane resonance. This resonance may underlie our novel finding of an association between CIN pauses and internally-generated slow wave events in sleeping non-human primates. Moreover, our method indicated that dendritic NaP and HCN currents were preferentially expressed in proximal dendrites. We validated the non-uniform distribution of NaP currents: pharmacologically; with two-photon imaging of dendritic back-propagating action potentials; and by demonstrating boosting of thalamic, but not cortical, inputs by NaP currents. Thus, the localization of active dendritic conductances in CIN dendrites mirrors the spatial distribution of afferent terminals and may promote their differential responses to thalamic vs. cortical inputs.

Scalable Thousand Channel Penetrating Microneedle Arrays on Flex for Multimodal and Large Area Coverage BrainMachine Interfaces

The Utah array powers cutting-edge projects for restoration of neurological function, such as BrainGate, but the underlying electrode technology has itself advanced little in the last three decades. Here, advanced dual-side lithographic microfabrication processes is exploited to demonstrate a 1024-channel penetrating silicon microneedle array (SiMNA) that is scalable in its recording capabilities and cortical coverage and is suitable for clinical translation. The SiMNA is the first penetrating microneedle array with a flexible backing that affords compliancy to brain movements. In addition, the SiMNA is optically transparent permitting simultaneous optical and electrophysiological interrogation of neuronal activity. The SiMNA is used to demonstrate reliable recordings of spontaneous and evoked field potentials and of single unit activity in chronically implanted mice for up to 196 days in response to optogenetic and to whisker air-puff stimuli. Significantly, the 1024-channel SiMNA establishes detailed spatiotemporal mapping of broadband brain activity in rats. This novel scalable and biocompatible SiMNA with its multimodal capability and sensitivity to broadband brain activity will accelerate the progress in fundamental neurophysiological investigations and establishes a new milestone for penetrating and large area coverage microelectrode arrays for brain-machine interfaces.

Neural Correlates of Multisensory Integration for Feedback Stabilization of the Wrist

Robust control of action relies on the ability to perceive, integrate, and act on information from multiple sensory modalities including vision and proprioception. How does the brain combine sensory information to regulate ongoing mechanical interactions between the body and its physical environment? Some behavioral studies suggest that the rules governing multisensory integration for action may differ from the maximum likelihood estimation rules that appear to govern multisensory integration for many perceptual tasks. We used functional magnetic resonance (MR) imaging techniques, a MR-compatible robot, and a multisensory feedback control task to test that hypothesis by investigating how neural mechanisms involved in regulating hand position against mechanical perturbation respond to the presence and fidelity of visual and proprioceptive information. Healthy human subjects rested supine in a MR scanner and stabilized their wrist against constant or pseudo-random torque perturbations imposed by the robot. These two stabilization tasks were performed under three visual feedback conditions: "No-vision": Subjects had to rely solely on proprioceptive feedback; "true-vision": visual cursor and hand motions were congruent; and "random-vision": cursor and hand motions were uncorrelated in time. Behaviorally, performance errors accumulated more quickly during trials wherein visual feedback was absent or incongruous. We analyzed blood-oxygenation level-dependent (BOLD) signal fluctuations to compare task-related activations in a cerebello-thalamo-cortical neural circuit previously linked with feedback stabilization of the hand. Activation in this network varied systematically depending on the presence and fidelity of visual feedback of task performance. Addition of task related visual information caused activations in the cerebello-thalamo-cortical network to expand into neighboring brain regions. Specific loci and intensity of expanded activity depended on the fidelity of visual feedback. Remarkably, BOLD signal fluctuations within these regions correlated strongly with the time series of proprioceptive errors-but not visual errors-when the fidelity of visual feedback was poor, even though visual and hand motions had similar variability characteristics. These results provide insight into the neural control of the body's physical interactions with its environment, rejecting the standard Gaussian cue combination model of multisensory integration in favor of models that account for causal structure in the sensory feedback.

Cortico-subcortical interactions in overlapping communities of edge functional connectivity

Both cortical and subcortical regions can be functionally organized into networks. Regions of the basal ganglia are extensively interconnected with the cortex via reciprocal connections that relay and modulate cortical function. Here we employ an edge-centric approach, which computes co-fluctuations among region pairs in a network to investigate the role and interaction of subcortical regions with cortical systems. By clustering edges into communities, we show that cortical systems and subcortical regions couple via multiple edge communities, with hippocampus and amygdala having a distinct pattern from striatum and thalamus. We show that the edge community structure of cortical networks is highly similar to one obtained from cortical nodes when the subcortex is present in the network. Additionally, we show that the edge community profile of both cortical and subcortical nodes can be estimates solely from cortico-subcortical interactions. Finally, we used a motif analysis focusing on edge community triads where a subcortical region coupled to two cortical regions and found that two community triads where one community couples the subcortex to the cortex were overrepresented. In summary, our results show organized coupling of the subcortex to the cortex that may play a role in cortical organization of primary sensorimotor/attention and heteromodal systems and puts forth the motif analysis of edge community triads as a promising method for investigation of communication patterns in networks.

Striatum expresses region-specific plasticity consistent with distinct memory abilities

The striatum mediates two learning modalities: goal-directed behavior in dorsomedial (DMS) and habits in dorsolateral (DLS) striata. The synaptic bases of these learnings are still elusive. Indeed, while ample research has described DLS plasticity, little remains known about DMS plasticity and its involvement in procedural learning. Here, we find symmetric and asymmetric anti-Hebbian spike-timing-dependent plasticity (STDP) in DMS and DLS, respectively, with opposite plasticity dominance upon increasing corticostriatal activity. During motor-skill learning, plasticity is engaged in DMS and striatonigral DLS neurons only during early learning stages, whereas striatopallidal DLS neurons are mobilized only during late phases. With a mathematical modeling approach, we find that symmetric anti-Hebbian STDP favors memory flexibility, while asymmetric anti-Hebbian STDP favors memory maintenance, consistent with memory processes at play in procedural learning.

Striatal synaptic adaptations in Parkinson's disease

The striatum is densely innervated by mesencephalic dopaminergic neurons that modulate acquisition and vigor of goal-directed actions and habits. This innervation is progressively lost in Parkinson's disease (PD), contributing to the defining movement deficits of the disease. Although boosting dopaminergic signaling with levodopa early in the course of the disease alleviates these deficits, later this strategy leads to the emergence of debilitating dyskinesia. Here, recent advances in our understanding of how striatal cells and circuits adapt to this progressive de-innervation and to levodopa therapy are discussed. First, we discuss how dopamine (DA) depletion triggers cell type-specific, homeostatic changes in spiny projection neurons (SPNs) that tend to normalize striatal activity but also lead to disruption of the synaptic architecture sculpted by experience. Second, we discuss the roles played by cholinergic and nitric oxide-releasing interneurons in these adaptations. Third, we examine recent work in freely moving mice suggesting that alterations in the spatiotemporal dynamics of striatal ensembles contributes to PD movement deficits. Lastly, we discuss recently published evidence from a progressive model of PD suggesting that contrary to the classical model, striatal pathway imbalance is necessary but not sufficient to produce frank parkinsonism.

A novel, interactive game to improve understanding of respiratory control pathways in first-year medical students

The physiology of respiration is a challenging subject for many medical students. To assist students, we have developed an active learning game that physically places students within a model outlining the respiratory control pathway. Participants were provided with a vodcast describing the physiology of respiratory control and instructed to view this before the activity. Once in the classroom, groups of students sat at tables marked to represent components of the respiratory control pathway (e.g., apneustic center, diaphragm etc.). Tables were connected with green and red ropes indicating excitatory or inhibitory effects, respectively. Students were presented with various scenarios (e.g., diabetic ketoacidosis) and asked to predict and illustrate the scenario's effect on subsequent steps in the respiratory pathway by waving the appropriate connecting rope. The next table would continue the pattern to simulate the collective physiological adaptation of the respiratory pathway. Thirty first-year medical students participated in this study. Following the activity, 25 out of the 30 participants completed an optional survey. The survey aimed to assess the benefits of adding this activity to our first-year medical curriculum to build a foundational understanding of the physiology of respiration. Responses were overwhelmingly favorable, and participants reported that playing the game significantly improved their perceived understanding of the physiology of respiratory control. All but one of the participants recommended using the activity in future classes. Because the small size of the study group may limit generalizability, future larger scale studies are planned.

From Progenitors to Progeny: Shaping Striatal Circuit Development and Function

Understanding how neurons of the striatum are formed and integrate into complex synaptic circuits is essential to provide insight into striatal function in health and disease. In this review, we summarize our current understanding of the development of striatal neurons and associated circuits with a focus on their embryonic origin. Specifically, we address the role of distinct types of embryonic progenitors, found in the proliferative zones of the ganglionic eminences in the ventral telencephalon, in the generation of diverse striatal interneurons and projection neurons. Indeed, recent evidence would suggest that embryonic progenitor origin dictates key characteristics of postnatal cells, including their neurochemical content, their location within striatum, and their long-range synaptic inputs. We also integrate recent observations regarding embryonic progenitors in cortical and other regions and discuss how this might inform future research on the ganglionic eminences. Last, we examine how embryonic progenitor dysfunction can alter striatal formation, as exemplified in Huntington's disease and autism spectrum disorder, and how increased understanding of embryonic progenitors can have significant implications for future research directions and the development of improved therapeutic options.SIGNIFICANCE STATEMENT This review highlights recently defined novel roles for embryonic progenitor cells in shaping the functional properties of both projection neurons and interneurons of the striatum. It outlines the developmental mechanisms that guide neuronal development from progenitors in the embryonic ganglionic eminences to progeny in the striatum. Where questions remain open, we integrate observations from cortex and other regions to present possible avenues for future research. Last, we provide a progenitor-centric perspective onto both Huntington's disease and autism spectrum disorder. We suggest that future investigations and manipulations of embryonic progenitor cells in both research and clinical settings will likely require careful consideration of their great intrinsic diversity and neurogenic potential.

Reduced Axon Calibre in the Associative Striatum of the Sapap3 Knockout Mouse

Pathological repetitive behaviours are a common feature of various neuropsychiatric disorders, including compulsions in obsessive-compulsive disorder or tics in Gilles de la Tourette syndrome. Clinical research suggests that compulsive-like symptoms are related to associative cortico-striatal dysfunctions, and tic-like symptoms to sensorimotor cortico-striatal dysfunctions. The Sapap3 knockout mouse (Sapap3-KO), the current reference model to study such repetitive behaviours, presents both associative as well as sensorimotor cortico-striatal dysfunctions. Previous findings point to deficits in both macro-, as well as micro-circuitry, both of which can be affected by neuronal structural changes. However, to date, structural connectivity has not been analysed. Hence, in the present study, we conducted a comprehensive structural characterisation of both associative and sensorimotor striatum as well as major cortical areas connecting onto these regions. Besides a thorough immunofluorescence study on oligodendrocytes, we applied AxonDeepSeg, an open source software, to automatically segment and characterise myelin thickness and axon area. We found that axon calibre, the main contributor to changes in conduction speed, is specifically reduced in the associative striatum of the Sapap3-KO mouse; myelination per se seems unaffected in associative and sensorimotor cortico-striatal circuits.

Cell Type-Specific Membrane Potential Changes in Dorsolateral Striatum Accompanying Reward-Based Sensorimotor Learning

The striatum integrates sensorimotor and motivational signals, likely playing a key role in reward-based learning of goal-directed behavior. However, cell type-specific mechanisms underlying reinforcement learning remain to be precisely determined. Here, we investigated changes in membrane potential dynamics of dorsolateral striatal neurons comparing naïve mice and expert mice trained to lick a reward spout in response to whisker deflection. We recorded from three distinct cell types: (i) direct pathway striatonigral neurons, which express type 1 dopamine receptors; (ii) indirect pathway striatopallidal neurons, which express type 2 dopamine receptors; and (iii) tonically active, putative cholinergic, striatal neurons. Task learning was accompanied by cell type-specific changes in the membrane potential dynamics evoked by the whisker deflection and licking in successfully-performed trials. Both striatonigral and striatopallidal types of striatal projection neurons showed enhanced task-related depolarization across learning. Striatonigral neurons showed a prominent increase in a short latency sensory-evoked depolarization in expert compared to naïve mice. In contrast, the putative cholinergic striatal neurons developed a hyperpolarizing response across learning, driving a pause in their firing. Our results reveal cell type-specific changes in striatal membrane potential dynamics across the learning of a simple goal-directed sensorimotor transformation, helpful for furthering the understanding of the various potential roles of different basal ganglia circuits.

Striatal GABA level is associated with sensory integration ability in individuals with low levels of negative schizotypy

Recent studies suggest that altered gamma-aminobutyric acidergic (GABAergic) function may result in multisensory integration deficits in schizophrenia. However, it is unclear whether the GABA level is abnormal in individuals with high levels of schizotypal traits and how it would correlate with sensory integration ability in these individuals. This study aimed to compare the GABA level between individuals with high and low levels of negative schizotypy, and examine the relationship between GABA levels and sensory integration ability in each group. In vivo GABA+ and N-acetylaspartate (NAA) levels in the striatum were measured using proton magnetic resonance imaging in 19 participants with high levels of negative schizotypy and 21 participants with low levels of negative schizotypy. The Sensory Integration subscale of the abridged version of the Cambridge Neurological Inventory was used. We examined the group differences in GABA+/NAA levels, and the correlation between striatal GABA+/NAA levels and sensory integration ability in each group. The two groups showed comparable levels of in-vivo GABA+/NAA. In-vivo GABA+/NAA levels were negatively correlated with sensory integration score in participants with low levels of negative schizotypy, but not in participants with high levels of negative schizotypy. Our findings indicate that the increased GABA level is correlated with better sensory integration ability in individuals with low levels of negative schizotypy, implicating the role of GABAergic function in multisensory integration. Unlike schizophrenia patients, individuals with high levels of schizotypy do not exhibit any abnormality in their GABAergic system and sensory integration ability.

Abnormal effective connectivity in the sensory network in writer's cramp

BACKGROUND

Writer's cramp (WC), a task specific form of dystonia, is considered to be a motor network disorder, but abnormal sensory tactile processing has also been acknowledged. The sensory spatial discrimination threshold (SDT) can be determined with a spatial acuity test (JVP domes). In addition to increased SDT, patients with WC exhibited dysfunctional sensory processing in the sensory cortex, insula, basal ganglia and cerebellum in a functional magnetic resonance imaging (fMRI) study while performing the spatial acuity test.

OBJECTIVES

To assess whether effective connectivity (EC) in the sensory network including cortical, basal ganglia, thalamic and cerebellar regions of interest in WC patients is abnormal.

METHODS

We used fMRI and applied a block design, while 19 WC patients and 13 age-matched healthy controls performed a spatial discrimination task. Before we assessed EC using dynamic causal modelling, we compared three model structures based on the current literature. We enclosed regions of interest that are established for sensory processing during right hand stimulation: Left thalamus, somatosensory, parietal and insular cortex, posterior putamen, and right cerebellum.

RESULTS

The EC analysis revealed task-dependent decreased unidirectional connectivity between the insula and the posterior putamen. The connectivity involving the primary sensory cortex, parietal cortex and cerebellum were not abnormal in WC. The two groups showed no differences in their behavioural data.

CONCLUSIONS

Perception and integration of sensory information requires the exchange of information between the insula cortex and the putamen, a sensory process that was disturbed in WC patients.

Complete representation of action space and value in all dorsal striatal pathways

The dorsal striatum plays a central role in the selection, execution, and evaluation of actions. An emerging model attributes action selection to the matrix and evaluation to the striosome compartment. Here, we use large-scale cell-type-specific calcium imaging to determine the activity of striatal projection neurons (SPNs) during motor and decision behaviors in the three major outputs of the dorsomedial striatum: Oprm1⁺ striosome versus D1⁺ direct and A2A⁺ indirect pathway SPNs. We find that Oprm1⁺ SPNs show complex tunings to simple movements and value-guided actions, which are conserved across many sessions in a single task but remap between contexts. During decision making, the SPN tuning profiles form a complete representation in which sequential SPN activity jointly encodes task progress and value. We propose that the three major output pathways in the dorsomedial striatum share a similarly complete representation of the entire action space, including task- and phase-specific signals of action value and choice.

Integrating the Roles of Midbrain Dopamine Circuits in Behavior and Neuropsychiatric Disease

Dopamine (DA) is a behaviorally and clinically diverse neuromodulator that controls CNS function. DA plays major roles in many behaviors including locomotion, learning, habit formation, perception, and memory processing. Reflecting this, DA dysregulation produces a wide variety of cognitive symptoms seen in neuropsychiatric diseases such as Parkinson’s, Schizophrenia, addiction, and Alzheimer’s disease. Here, we review recent advances in the DA systems neuroscience field and explore the advancing hypothesis that DA’s behavioral function is linked to disease deficits in a neural circuit-dependent manner. We survey different brain areas including the basal ganglia’s dorsomedial/dorsolateral striatum, the ventral striatum, the auditory striatum, and the hippocampus in rodent models. Each of these regions have different reported functions and, correspondingly, DA’s reflecting role in each of these regions also has support for being different. We then focus on DA dysregulation states in Parkinson’s disease, addiction, and Alzheimer’s Disease, emphasizing how these afflictions are linked to different DA pathways. We draw upon ideas such as selective vulnerability and region-dependent physiology. These bodies of work suggest that different channels of DA may be dysregulated in different sets of disease. While these are great advances, the fine and definitive segregation of such pathways in behavior and disease remains to be seen. Future studies will be required to define DA’s necessity and contribution to the functional plasticity of different striatal regions.

Early Sensory Deprivation Leads to Differential Inhibitory Changes in the Striatum During Learning

The corticostriatal circuit has been identified as a vital pathway for associative learning. However, how learning is implemented when the sensory striatum is permanently impaired remains unclear. Using chemogenetic techniques to suppress layer five auditory cortex (AC) input to the auditory striatum, learning of a sound discrimination task was significantly impacted in freely moving Mongolian gerbils, in particular when this suppression occurs early on during learning. Whole-cell recordings sampled throughout learning revealed a transient reduction in postsynaptic (GABAA) inhibition in both striatal D1 and D2 cells in normal-hearing gerbils during task acquisition. In contrast, when the baseline striatal inhibitory strengths and firing rates were permanently reduced by a transient period of developmental sensory deprivation, learning was accompanied by augmented inhibition and increased firing rates. Direct manipulation of striatal inhibition in vivo and in vitro revealed a key role of the transient inhibitory changes in task acquisition. Together, these results reveal a flexible corticostriatal inhibitory synaptic plasticity mechanism that accompanies associative auditory learning.

Dopamine differentially modulates the size of projection neuron ensembles in the intact and dopamine-depleted striatum

Dopamine (DA) is a critical modulator of brain circuits that control voluntary movements, but our understanding of its influence on the activity of target neurons in vivo remains limited. Here, we use two-photon Ca2+ imaging to monitor the activity of direct and indirect-pathway spiny projection neurons (SPNs) simultaneously in the striatum of behaving mice during acute and prolonged manipulations of DA signaling. We find that increasing and decreasing DA biases striatal activity toward the direct and indirect pathways, respectively, by changing the overall number of SPNs recruited during behavior in a manner not predicted by existing models of DA function. This modulation is drastically altered in a model of Parkinson's disease. Our results reveal a previously unappreciated population-level influence of DA on striatal output and provide novel insights into the pathophysiology of Parkinson's disease.

Altered Sensory Representations in Parkinsonian Cortical and Basal Ganglia Networks

In parkinsonian conditions, network dynamics in the cortical and basal ganglia circuits present abnormal oscillations and periods of high synchrony, affecting the functionality of multiple striatal regions including the sensorimotor striatum. However, it is still unclear how these altered dynamics impact on sensory processing, a key feature for motor control that is severely impaired in parkinsonian patients. A major confound is that pathological dynamics in sensorimotor networks may elicit unspecific motor responses that may alter sensory representations through sensory feedback, making it difficult to disentangle motor and sensory components. To address this issue, we studied sensory processing using an anesthetized model with robust sensory representations throughout cortical and basal ganglia sensory regions and limited motor confounds in control and hemiparkinsonian rats. A general screening of sensory-evoked activity in large populations of neurons recorded in the primary sensory cortex (S1), dorsolateral striatum (DLS) and substantia nigra pars reticulata (SNr) revealed increased excitability and altered sensory representations in the three regions. Further analysis revealed uncoordinated population dynamics between DLS and S1/SNr. Finally, DLS lesions in hemiparkinsonian animals partially recovered population dynamics and execution in the rotarod.

Optogenetic fUSI for brain-wide mapping of neural activity mediating collicular-dependent behaviors

Neuronal cell types are arranged in brain-wide circuits that guide behavior. In mice, the superior colliculus innervates a set of targets that direct orienting and defensive actions. We combined functional ultrasound imaging (fUSI) with optogenetics to reveal the network of brain regions functionally activated by four collicular cell types. Stimulating each neuronal group triggered different behaviors and activated distinct sets of brain nuclei. This included regions not previously thought to mediate defensive behaviors, for example, the posterior paralaminar nuclei of the thalamus (PPnT), which we show to play a role in suppressing habituation. Neuronal recordings with Neuropixels probes show that (1) patterns of spiking activity and fUSI signals correlate well in space and (2) neurons in downstream nuclei preferentially respond to innately threatening visual stimuli. This work provides insight into the functional organization of the networks governing innate behaviors and demonstrates an experimental approach to explore the whole-brain neuronal activity downstream of targeted cell types.