Bilateral Globus Pallidus Externus Deep Brain Stimulation for the Treatment of Refractory Tourette Syndrome: An Open Clinical Trial

OBJECTIVES

We have previously proposed that Tourette syndrome (TS) is the clinical expression of the hyperactivity of globus pallidus externus (GPe) and various cortical areas. This study was designed to test this hypothesis by verifying the efficacy and safety of bilateral GPe deep brain stimulation (DBS) for treating refractory TS.

MATERIALS AND METHODS

In this open clinical trial, 13 patients were operated on. Target coordinates (center of GPe) were obtained by direct visualization. Physiological mapping was performed with macrostimulation and microrecording. Primary and secondary outcome measures were, respectively, responder and improvement rates of TS and comorbidities, according to pre- and postoperative scores on the following assessment instruments: Yale Global Tic Severity Scale, Yale-Brown Obsessive Compulsive Scale, Beck Depression Inventory/Hamilton Depression Rating Scale, Beck Anxiety Inventory/Hamilton Anxiety Rating Scale, and Concentrated Attention test.

RESULTS

Intraoperative stimulation (100 Hz/5.0V) did not produce any adverse effects or impact on tics. Microrecording revealed bursting cells discharging synchronously with tics in the central part of the dorsal half of GPe. Patients were followed up for a mean of 61.46±48.50 months. Responder rates were 76.9%, 75%, 71.4%, 71.4%, and 85.7%, respectively, for TS, obsessive-compulsive disorder (OCD), depression, anxiety, and attention deficit hyperactivity disorder. Mean improvements among responders in TS, OCD, depression, and anxiety were 77.4%, 74.7%, 89%, and 84.8%, respectively. After starting stimulation, tic improvement was usually delayed, taking up to ten days to manifest. Afterward, it increased over time, usually reaching its maximum at approximately one year postoperatively. The best stimulation parameters were 2.3V to 3.0V, 90 to 120 μsec, and 100 to 150 Hz, and the most effective contacts were the two dorsal ones. Two complications were registered: reversible impairment of previous depression and transient unilateral bradykinesia.

CONCLUSIONS

Bilateral GPe-DBS proved to be low risk and quite effective for treating TS and comorbidities, ratifying the pathophysiological hypothesis that led to this study. Moreover, it compared favorably with DBS of other targets currently in use.

SB-258585 reduces food motivation while blocking 5-HT6 receptors in the non-human primate striatum

The interest in new 5-HT₆ agents stems from their ability to modulate cognition processing, food motivation and anxiety-like behaviors. While these findings come primarily from rodent studies, no studies on primates have been published. Furthermore, our understanding of where and how they act in the brain remains limited. Although the striatum is involved in all of these processes and expresses the highest levels of 5-HT₆ receptors, few studies have focused on it. We thus hypothesized that 5-HT6 receptor blockade would influence food motivation and modulate behavioral expression in non-human primates through striatal 5-HT6 receptors. This study thus aimed to determine the effects of acute administration of the SB-258585 selective 5-HT6 receptor antagonist on the feeding motivation and behaviors of six male macaques. Additionally, we investigated potential 5-HT6 targets using PET imaging to measure 5-HT6 receptor occupancy throughout the brain and striatal subregions. We used a food-choice task paired with spontaneous behavioral observations, checking 5-HT6 receptor occupancy with the specific PET imaging [18F]2FNQ1P radioligand. We demonstrated, for the first time in non-human primates, that modulation of 5-HT6 transmission, most likely through the striatum (the putamen and caudate nucleus), significantly reduces food motivation while exhibiting variable, weaker effects on behavior. While these results are consistent with the literature showing a decrease in food intake in rodents and proposing that 5-HT6 receptor antagonists can be used in obesity treatment, they question the antagonists' anxiolytic potential.

Distinct neural adaptations to time demand in the striatum and the hippocampus

How do neural codes adjust to track time across a range of resolutions, from milliseconds to multi-seconds, as a function of the temporal frequency at which events occur? To address this question, we studied time-modulated cells in the striatum and the hippocampus, while macaques categorized three nested intervals within the sub-second or the supra-second range (up to 1, 2, 4, or 8 s), thereby modifying the temporal resolution needed to solve the task. Time-modulated cells carried more information for intervals with explicit timing demand, than for any other interval. The striatum, particularly the caudate, supported the most accurate temporal prediction throughout all time ranges. Strikingly, its temporal readout adjusted non-linearly to the time range, suggesting that the striatal resolution shifted from a precise millisecond to a coarse multi-second range as a function of demand. This is in line with monkey's behavioral latencies, which indicated that they tracked time until 2 s but employed a coarse categorization strategy for durations beyond. By contrast, the hippocampus discriminated only the beginning from the end of intervals, regardless of the range. We propose that the hippocampus may provide an overall poor signal marking an event's beginning, whereas the striatum optimizes neural resources to process time throughout an interval adapting to the ongoing timing necessity.

Selective striatal fast-spiking interneuron inhibition induces cortical seizure

Whether striatal fast-spiking interneurons are involved in cortical synchronization remains elusive. We performed acute microinjections of a selective FSI-AMPA receptor antagonist into the sensorimotor striatum of non-human primates to verify whether selective FSI inhibition within the sensorimotor striatum could potentially modify cortical excitability, thereby triggering focal seizures. Experiments were performed on three fascicularis monkeys. During each experimental session, low volumes of IEM-1460 (4-8 μL) were injected slowly at 1 μL/min. Spontaneous behavioral changes were classified according to the Racine scale modified for primates. These induced motor behaviors were correlated with electroencephalographic (EEG and EMG) measures. Power spectrum and time-frequency analysis were performed and compared between each period of interest. Pharmacological selective inhibition of striatal fast-spiking INs induced focal motor seizures. Back averaging confirmed that myoclonic activity was closely linked to cortical spikes-and-waves epileptic activity, with a significant increase in cortical EEG power in all studied frequency bands (p < .0001). Thus, striatal FSIs likely play a role in controlling cortical excitability through the cortico-striato-thalamo-cortical pathway. They may contribute to the pathophysiology of focal motor epilepsies by modulating the threshold at which focal motor seizures are triggered.

An Update on the Diagnosis and Management of Tic Disorders

Tic disorders (TDs) are a group of common neuropsychiatric disorders of childhood and adolescence. TDs may impact the physical, emotional, and social well-being of the affected person. In this review, we present an update on the clinical manifestations, pathophysiology, diagnosis, and treatment of TDs. We searched the PubMed database for articles on tics and Tourette syndrome. More than 400 articles were reviewed, of which 141 are included in this review. TDs are more prevalent in children than in adults and in males than in females. It may result from a complex interaction between various genetic, environmental, and immunological factors. Dysregulation in the cortico-striato-pallido-thalamo-cortical network is the most plausible pathophysiology resulting in tics. TD is a clinical diagnosis based on clinical features and findings on neurological examination, especially the identification of tic phenomenology. In addition to tics, TD patients may have sensory features, including premonitory urge; enhanced and persistent sensitivity to non-noxious external or internal stimuli; and behavioral manifestations, including attention deficit hyperactivity disorders, obsessive-compulsive disorders, and autism spectrum disorders. Clinical findings of hyperkinetic movements that usually mimic tics have been compared and contrasted with those of TD. Patients with TD may not require specific treatment if tics are not distressing. Psychoeducation and supportive therapy can help reduce tics when combined with medication. Dispelling myths and promoting acceptance are important to improve patient outcomes. Using European, Canadian, and American guidelines, the treatment of TD, including behavioral therapy, medical therapy, and emerging/experimental therapy, has been discussed.

Apathy in Parkinson's Disease: Clinical Patterns and Neurobiological Basis

Apathy is commonly defined as a loss of motivation leading to a reduction in goal-directed behaviors. This multidimensional syndrome, which includes cognitive, emotional and behavioral components, is one of the most prevalent neuropsychiatric features of Parkinson's disease (PD). It has been established that the prevalence of apathy increases as PD progresses. However, the pathophysiology and anatomic substrate of this syndrome remain unclear. Apathy seems to be underpinned by impaired anatomical structures that link the prefrontal cortex with the limbic system. It can be encountered in the prodromal stage of the disease and in fluctuating PD patients receiving bilateral chronic subthalamic nucleus stimulation. In these stages, apathy may be considered as a disorder of motivation that embodies amotivational behavioral syndrome, is underpinned by combined dopaminergic and serotonergic denervation and is dopa-responsive. In contrast, in advanced PD patients, apathy may be considered as cognitive apathy that announces cognitive decline and PD dementia, is underpinned by diffuse neurotransmitter system dysfunction and Lewy pathology spreading and is no longer dopa-responsive. In this review, we discuss the clinical patterns of apathy and their treatment, the neurobiological basis of apathy, the potential role of the anatomical structures involved and the pathways in motivational and cognitive apathy.

Transdiagnostic brain correlates of self-reported trait impulsivity: A dimensional structure-symptom investigation

Impulsivity transcends psychiatric diagnoses and is often related to anhedonia. This ad hoc cross-sectional investigation explored 1) whether self-reported trait impulsivity mapped onto a common structural brain substrate across healthy controls (HCs) and psychiatric patients, and 2) in a more exploratory fashion, whether impulsivity and anhedonia were related to each other and shared overlapping brain correlates. Structural magnetic resonance imaging (sMRI) datasets from 234 participants including HCs (n = 109) and patients with opioid use disorder (OUD, n = 22), cocaine use disorder (CUD, n = 43), borderline personality disorder (BPD, n = 45) and schizophrenia (SZ, n = 15) were included. Trait impulsivity was measured with the Barratt Impulsiveness Scale (BIS-11) and anhedonia with a subscore of the Beck Depression Inventory (BDI). BIS-11 global score data were available for the entire sample, while data on the BIS-11 2nd order factors attentional, motor and non-planning were additionally in hand for a subsample consisting of HCs, OUD and BPD patients (n = 116). Voxel-based morphometry analyses were conducted for identifying dimensional associations between grey matter volume and impulsivity/anhedonia. Partial correlations were further performed to exploratory test the relationships between impulsivity and anhedonia and their corresponding volumetric brain substrates. Volume of the left opercular part of the inferior frontal gyrus (IFG) was negatively related to global impulsivity across the entire sample and specifically to motor impulsivity in the subsample of HCs, OUD and BPD patients. Across patients anhedonia expression was negatively correlated with left putamen volume. Although there was no relationship between global impulsivity and anhedonia across all patients, only across OUD and BPD patients anhedonia was positively associated with attentional impulsivity. Finally, also across OUD and BPD patients, motor impulsivity associated left IFG volume was positively linked with anhedonia-associated volume in the left putamen. Our findings suggest a critical role of left IFG volume in self-reported global impulsivity across healthy participants and patients with substance use disorder, BPD and SZ. Preliminary findings in OUD and BPD patients further suggests associations between impulsivity and anhedonia that are related to grey matter reductions in the left IFG and putamen.

Nine-month-long Social Isolation Changes the Levels of Monoamines in the Brain Structures of Rats: A Comparative Study of Neurochemistry and Behavior

Social isolation (SI) is chronic psycho-emotional stress for humans and other socially living species. There are few comparative studies that have measured monoamine levels in brain structures in male and female rats subjected to SI. Existing data is highly controversial. In our recent study, we investigated behavioral effects of SI prolonged up to 9 months on a rather large sample of 69 male and female Wistar rats. In the present study, we measured the levels of monoamines-norepinephrine (NE), dopamine (DA), 5-hydroxytryptamine (5-HT), and DA and 5-HT metabolites-in the brain structures of 40 rats from the same sample. The single-housed rats of both sexes showed hyperactivity and reduced reactivity to novelty in the Open Field test, and impaired passive avoidance learning. Regardless of their sex, by the time of sacrifice, the single-housed rats weighed less and had lower pain sensitivity and decreased anxiety compared with group-housed animals. SI decreased NE levels in the hippocampus and increased them in the striatum. SI induced functional activation of the DA-ergic system in the frontal cortex and hypothalamus, with increased DA and 3-methoxytyramine levels. SI-related changes were found in the 5-HT-ergic system: 5-HT levels increased in the frontal cortex and striatum, while 5-hydroxyindoleacetic acid only increased in the frontal cortex. We believe that SI prolonged for multiple months could be a valuable model for comparative analysis of the behavioral alterations and the underlying molecular processes in dynamics of adaptation to chronic psychosocial stress in male and female rats in relation to age-dependent changes.

Impulsive and compulsive behaviors can be induced by opposite GABAergic dysfunctions inside the primate ventral pallidum

Introduction: The ventral pallidum (VP) is central in the limbic Basal Ganglia circuit, controlling both appetitive (approach) and aversive (avoidance) motivated behaviors. Nevertheless, VP involvement in pathological aspects remains unclear, especially in the behavioral expression of different motivational dysfunctions. This study aimed to investigate how the VP contributes to the expression of abnormal behaviors via opposite GABAergic dysfunctions. Methods: Opposite GABAergic dysfunctions were induced by injecting muscimol (a GABA_A agonist) and bicuculline (a GABA_A antagonist) into monkeys. We determined the effects of both substances on self-initiated behaviors in lab-chair and in free-moving home-cage contexts in six monkeys, and in two animals performing an approach-avoidance task in appetitive and aversive contexts. Results: While the self-initiated behaviors induced by bicuculline injections in VP were characterized by compulsive behaviors such as repetitive grooming and self-biting, muscimol injections induced impulsive behaviors including limb movements in a lab-chair context and exploration behaviors in a free-moving context. More specific behavioral effects were observed in the approach-avoidance task. The muscimol injections induced premature responses and erroneous screen touches, which characterize impulsive and attention disorders, while the bicuculline injections into the VP increased passive avoidance (non-initiated action) and task-escape in an aversive context, suggesting an anxiety disorder. Conclusions: These results show that activating or blocking GABAergic transmission in the VP impairs motivated behaviors. Furthermore, the behavioral expressions produced by these opposite disturbances show that the VP could be involved in anxiety-driven compulsive disorders, such as OCD, as well as in impulsive disorders motivated by attention deficits or reward-seeking, as seen in ADHD or impulse control disorders.

Neural mapping of anhedonia across psychiatric diagnoses: A transdiagnostic neuroimaging analysis

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Anhedonia is present in many different psychiatric disorders.

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Anhedonia has been associated with abnormal reward-related striatal dopamine functioning.

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This study tested whether transdiagnostic anhedonia expression mapped onto striatal volume.

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Our findings suggest volumetric abnormalities in the putamen and cerebellum as a common neural substrate of anhedonia severity that cut across psychiatric entities.

Anhedonia has been associated with abnormal reward-related striatal dopamine functioning in patients with different psychiatric disorders. Here, we tested whether anhedonia expression mapped onto striatal volume across several psychiatric diagnoses.

T1-weighted images from 313 participants including 89 healthy controls (HC), 22 patients with opioid use disorder (OUD), 50 patients with major depressive disorder (MDD), 45 patients with borderline personality disorder (BPD), 49 patients with first-episode psychosis (FEP), 43 patients with cocaine use disorder (CUD) and 15 patients with schizophrenia (SZ) were included. Anhedonia was assessed with subscores of the Beck Depression Inventory (BDI) and/or the Scale for the Assessment of Negative Symptoms (SANS). Voxel-based morphometry (VBM) was conducted for identifying dimensional symptom-structure associations using region of interest (ROI, dorsal and ventral striatum) and whole-brain analyses, as well as for group comparisons of striatal volume.

ROI analyses revealed significant negative relationships between putamen volume and BDI and SANS anhedonia scores across OUD, MDD, BPD, CUD and SZ patients (n = 175) and MDD, FEP and SZ patients (n = 114), respectively. Whole-brain VBM analyses confirmed these associations and further showed negative relationships between anhedonia severity and volume of the bilateral cerebellum. There were group differences in right accumbens volume, which however were not related to anhedonia expression across the different diagnoses.

Our findings indicate volumetric abnormalities in the putamen and cerebellum as a common neural substrate of anhedonia severity that cut across psychiatric entities.

Visualizing Oscillations in Brain Slices With Genetically Encoded Voltage Indicators

Genetically encoded voltage indicators (GEVIs) expressed pan-neuronally were able to optically resolve bicuculline induced spontaneous oscillations in brain slices of the mouse motor cortex. Three GEVIs were used that differ in their timing of response to voltage transients as well as in their voltage ranges. The duration, number of cycles, and frequency of the recorded oscillations reflected the characteristics of each GEVI used. Multiple oscillations imaged in the same slice never originated at the same location, indicating the lack of a “hot spot” for induction of the voltage changes. Comparison of pan-neuronal, Ca²⁺/calmodulin-dependent protein kinase II α restricted, and parvalbumin restricted GEVI expression revealed distinct profiles for the excitatory and inhibitory cells in the spontaneous oscillations of the motor cortex. Resolving voltage fluctuations across space, time, and cell types with GEVIs represent a powerful approach to dissecting neuronal circuit activity.

Selective serotonin reuptake inhibitor treatment retunes emotional valence in primate ventral striatum

Selective serotonin reuptake inhibitors (SSRIs) are widely used to treat psychiatric disorders with affective biases such as depression and anxiety. How SSRIs exert a beneficial action on emotions associated with life events is still unknown. Here we ask whether and how the effectiveness of the SSRI fluoxetine is underpinned by neural mechanisms in the ventral striatum. To address these issues, we studied the spiking activity of neurons in the ventral striatum of monkeys during an approach-avoidance task in which the valence assigned to sensory stimuli was manipulated. Neural responses to positive and negative events were measured before and during a 4-week treatment with fluoxetine. We conducted PET scans to confirm that fluoxetine binds within the ventral striatum at a therapeutic dose. In our monkeys, fluoxetine facilitated approach of rewards and avoidance of punishments. These beneficial effects were associated with changes in tonic and phasic activities of striatal neurons. Fluoxetine increased the spontaneous firing rate of striatal neurons and amplified the number of cells responding to rewards versus punishments, reflecting a drug-induced positive shift in the processing of emotionally valenced information. These findings reveal how SSRI treatment affects ventral striatum neurons encoding positive and negative valence and striatal signaling of emotional information. In addition to a key role in appetitive processing, our results shed light on the involvement of the ventral striatum in aversive processing. Together, the ventral striatum appears to play a central role in the action of SSRIs on emotion processing biases commonly observed in psychiatric disorders.

Induction of Ticlike Involuntary Movements in Rats by Striatotomy and Subsequent Neurochemical Sensitization

OBJECTIVE

It has been proposed that Tourette syndrome is associated with dysfunction in widespread cortical areas and globus pallidus externus hyperactivity secondary to dopaminergic hyperactivity and serotonergic/dynorphinergic hypoactivity. The main objective of this study was to test this hypothesis by developing an animal model of Tourette syndrome via striatotomy, followed by administration of drugs that mimic the neurotransmitter environment, so as to induce globus pallidus externus hyperactivity.

METHODS

Rats were assigned to 3 groups: stereotactic striatotomy (STT) and striatal sham -lesion (SHAM) groups, treated with anterior and posterior striatum procedures in both hemispheres, and a group of nonoperated animals (NAIVE). Postoperatively, all rodents were blindly administered 3 drug protocols: levodopa/benserazide; levodopa/benserazide/ergotamine/naloxone (MIX); and saline. The animals were filmed at the peak action of these drugs. The videos were evaluated by a single blinded researcher.

RESULTS

Six types of involuntary movements (IMs) were observed: cephalic, trunk jerks, oromandibular, forepaw jerks, dystonic, and locomotive. The number of animals with IM and the mean number of IM after both levodopa/benserazide and MIX was significantly higher in the STT compared with the SHAM and NAIVE groups. In the SHAM and NAIVE, MIX was superior to levodopa/benserazide in the induction of IM. In the STT, MIX was superior to levodopa/benserazide in the induction of trunk jerks. Appendicular IM were more common after posterior than after anterior striatotomy.

CONCLUSIONS

These results show that striatotomy, followed by administration of levodopa/benserazide alone or associated with ergotamine and naloxone, is efficacious in inducing IM, supporting the hypothesis that led to this study.

Dorsal and ventral striatal neuronal subpopulations differentially disrupt male mouse copulatory behavior

The specific role of the striatum, especially its dorsolateral (DLS) and dorsomedial (DMS) parts, in male copulatory behavior is still debated. In order to clarify their contribution to male sexual behavior, we specifically ablated the major striatal neuronal subpopulations, direct and indirect medium spiny neurons (dMSNs and iMSNs) in DMS or DLS, and dMSNs, iMSNs and cholinergic interneurons in nucleus accumbens (NAc), The main results of this study can be summarized as follows: In DMS, dMSN ablation causes a reduction in the percent of mice that mount a receptive female, and a complex alteration in the parameters of the copulatory performance, that is largely opposite to the alterations induced by iMSN ablation. In DLS, dMSN ablation causes a widespread alteration in the copulatory behavior parameters, that tends to disappear at repetition of the test; iMSN ablation induces minor copulatory behavior alterations that are complementary to those observed after dMSN ablation. In NAc, dMSN ablation causes a marked reduction in the percent of mice that mount a receptive female and a disruption of copulatory behavior, while iMSN ablation induces minor copulatory behavior alterations that are opposite to those observed with dMSN ablation, and cholinergic neuron ablation induces a selective decrease in mount latency. Overall, present data point to a complex region and cell-specific contribution to copulatory behavior of the different neuronal subpopulations of both dorsal and ventral striatum, with a prominent role of the dMSNs of the different subregions.

Social impairments in mice lacking the voltage-gated potassium channel Kv3.1

Parvalbumin (PV)-expressing neurons have been implicated in the pathology of autism spectrum disorders (ASD). Loss of PV expression and/or reduced number of PV-expressing neurons have been reported not only in genetic and environmental rodent models of ASD, but also in post-mortem analyses of brain tissues from ASD vs. healthy control human subjects. PV-expressing neurons play a pivotal role in the maintenance of the balance between excitation and inhibition within neural circuits in part because of their fast-spiking properties. Their high firing rate is mostly regulated by the voltage-gated potassium channel Kv3.1. It is yet unknown whether disturbances in the electrophysiological properties of PV-expressing neurons per se can lead to behavioral disturbances. We assessed locomotor activity, social interaction, recognition and memory, and stereotypic behaviors in Kv3.1 wild-type (WT) and knockout (KO) mice. We then used Western Blot analyses to measure the impact of Kv3.1 deficiency on markers of GABA transmission (PV and GAD67) and neural circuit activity (Egr1). Deficiency in Kv3.1 channel is sufficient to induce social deficits, hyperactivity and stereotypic behaviors. These behavioral changes were independent of changes in GAD67 levels and associated with increased levels of PV protein in the prefrontal cortex and striatum. These findings reveal that a loss of PV expression is not a necessary factor to induce an ASD-like phenotype in mice and support the need for further investigation to fully understand the contribution of PV-expressing neurons to ASD pathology.

Causal Evidence for Induction of Pessimistic Decision-Making in Primates by the Network of Frontal Cortex and Striosomes

Clinical studies have shown that patients with anxiety disorders exhibited coactivation of limbic cortices and basal ganglia, which together form a large-scale brain network. The mechanisms by which such a large-scale network could induce or modulate anxiety-like states are largely unknown. This article reviews our experimental program in macaques demonstrating a causal involvement of local striatal and frontal cortical sites in inducing pessimistic decision-making that underlies anxiety. Where relevant, we related these findings to the wider literature. To identify such sites, we have made a series of methodologic advances, including the combination of causal evidence for behavioral modification of pessimistic decisions with viral tracing methods. Critically, we introduced a version of the classic approach-avoidance (Ap-Av) conflict task, modified for use in non-human primates. We performed microstimulation of limbic-related cortical regions and the striatum, focusing on the pregenual anterior cingulate cortex (pACC), the caudal orbitofrontal cortex (cOFC), and the caudate nucleus (CN). Microstimulation of localized sites within these regions induced pessimistic decision-making by the monkeys, supporting the idea that the focal activation of these regions could induce an anxiety-like state, which subsequently influences decision-making. We further performed combined microstimulation and tract-tracing experiments by injecting anterograde viral tracers into focal regions, at which microstimulation induced increased avoidance. We found that effective stimulation sites in both pACC and cOFC zones projected preferentially to striosomes in the anterior striatum. Experiments in rodents have shown that the striosomes in the anterior striatum project directly to the dopamine-containing cells in the substantia nigra, and we have found evidence for a functional connection between striosomes and the lateral habenular region in which responses to reward are inhibitory. We present here further evidence for network interactions: we show that the pACC and cOFC project to common structures, including not only the anterior parts of the striosome compartment but also the tail of the CN, the subgenual ACC, the amygdala, and the thalamus. Together, our findings suggest that networks having pACC and cOFC as nodes share similar features in their connectivity patterns. We here hypothesize, based on these results, that the brain sites related to pessimistic judgment are mediated by a large-scale brain network that regulates dopaminergic functions and includes striosomes and striosome-projecting cortical regions.

Temporal discounting in adolescents and adults with Tourette syndrome

Tourette syndrome is a neurodevelopmental disorder associated with hyperactivity in dopaminergic networks. Dopaminergic hyperactivity in the basal ganglia has previously been linked to increased sensitivity to positive reinforcement and increases in choice impulsivity. In this study, we examine whether this extends to changes in temporal discounting, where impulsivity is operationalized as an increased preference for smaller-but-sooner over larger-but-later rewards. We assessed intertemporal choice in two studies including nineteen adolescents (age: mean[sd] = 14.21[±2.37], 13 male subjects) and twenty-five adult patients (age: mean[sd] = 29.88 [±9.03]; 19 male subjects) with Tourette syndrome and healthy age- and education matched controls. Computational modeling using exponential and hyperbolic discounting models via hierarchical Bayesian parameter estimation revealed reduced temporal discounting in adolescent patients, and no evidence for differences in adult patients. Results are discussed with respect to neural models of temporal discounting, dopaminergic alterations in Tourette syndrome and the developmental trajectory of temporal discounting. Specifically, adolescents might show attenuated discounting due to improved inhibitory functions that also affect choice impulsivity and/or the developmental trajectory of executive control functions. Future studies would benefit from a longitudinal approach to further elucidate the developmental trajectory of these effects.

Examining the neural antecedents of tics in Tourette syndrome using electroencephalography

Tourette syndrome (TS) is a neurodevelopmental disorder characterized by the occurrence of motor and vocal tics. TS is associated with cortical-striatal-thalamic-cortical circuit dysfunction and hyper-excitability of cortical limbic and motor regions that lead to the occurrence of tics. Importantly, individuals with TS often report that their tics are preceded by premonitory sensory/urge phenomena (PU) that are described as uncomfortable bodily sensations that precede the execution of a tic and are experienced as an urge for motor discharge. While tics are most often referred to as involuntary movements, it has been argued by some that tics should be viewed as voluntary movements that are executed in response to the presence of PU. To investigate this issue further, we conducted a study using electroencephalography (EEG). We recorded movement-related EEG (mu- and beta-band oscillations) during (1) the immediate period leading up to the execution of voluntary movements by a group of individuals with TS and a group of matched healthy control participants, and (2) the immediate period leading up to the execution of a tic in a group of individuals with TS. We demonstrate that movement-related mu and beta oscillations are not reliably observed prior to tics in individuals with TS. We interpret this effect as reflecting the greater involvement of a network of brain areas, including the insular and cingulate cortices, the basal ganglia and the cerebellum, in the generation of tics in TS. We also show that beta-band desynchronization does occur when individuals with TS initiate voluntary movements, but, in contrast to healthy controls, desynchronization of mu-band oscillations is not observed during the execution of voluntary movements for individuals with TS. We interpret this finding as reflecting a dysfunction of physiological inhibition in TS, thereby contributing to an impaired ability to suppress neuronal populations that may compete with movement preparation processes.

Dissociation of tic generation from tic expression during the sleep-wake cycle

Motor tics, the hallmark of Tourette syndrome (TS), are modulated by different behavioral and environmental factors. A major modulating factor is the sleep-wake cycle in which tics are attenuated to a large extent during sleep. This study demonstrates a similar reduction in tic expression during sleep in an animal model of chronic tic disorders and investigates the underlying neural mechanism. We recorded the neuronal activity during spontaneous sleep-wake cycles throughout continuous GABA_A antagonist infusion into the striatum. Analysis of video streams and concurrent kinematic assessments indicated tic reduction during sleep in both frequency and intensity. Extracellular recordings in the striatum revealed a state-dependent dissociation between motor tic expression and their macro-level neural correlates ("LFP spikes") during the sleep-wake cycle. Local field potential (LFP) spikes, which are highly correlated with tic expression during wakefulness, persisted during tic-free sleep and did not change their properties despite the reduced behavioral expression. Local, micro-level, activity near the infusion site was time-locked to the LFP spikes during wakefulness, but this locking decreased significantly during sleep. These results suggest that whereas LFP spikes encode motor tic generation and feasibility, the behavioral expression of tics requires local striatal neural activity entrained to the LFP spikes, leading to the propagation of the activity to downstream targets and consequently their motor expression. These findings point to a possible mechanism for the modulation of tic expression in patients with TS during sleep and potentially during other behavioral states.

Reward sensitivity and action in Parkinson's disease patients with and without apathy

Clinical apathy results in dysfunction of goal directed behaviour, a key component of which is the initiation of action. Previous work has suggested that blunting of reward sensitivity is an important mechanism underlying apathy. However, an additional component might be impoverished initiation of action itself. This study aims to investigate the link between motivation and motor output and its association with apathy and dopamine. An oculomotor task that measures pupillary and saccadic response to monetary incentives was used to assess reward sensitivity, first in 23 young and 18 elderly controls, and then in 22 patients with Parkinson's disease tested ON and OFF dopaminergic medication. To distinguish between pupillary responses to anticipated reward alone versus responses associated with motor preparation, a saccadic 'go/no-go' task was performed. Half of the trials required a saccade to be initiated to receive a reward and in the remaining trials no action was required but reward was still obtained. No significant difference in pupil response was demonstrated between the two conditions in all groups tested, suggesting pupillary responses to rewards are not contingent upon motor preparation in Parkinson's disease. Being ON or OFF dopamine did not influence this response either. Previous work demonstrated associations between apathy and pupillary reward insensitivity in Parkinson's disease. Here we observed this effect only when an action was required to receive a reward, and only in the ON state. These findings suggest that apathy in Parkinson's disease is linked to reduced reward sensitivity and that this is most prominently observed when actions have to be initiated to rewarding goals, with the effect modulated by being ON dopaminergic medication. OFF medication, there was no such strong relationship, and similarly in the 'no-go' conditions, either ON or OFF dopaminergic drugs. The results provide preliminary data which suggest that apathy in Parkinson's disease is associated with a reduction in reward sensitivity and this is most evident when associated with initiation of goal directed actions in the presence of adequate dopamine.

Acute Striato-Cortical Synchronization Induces Focal Motor Seizures in Primates

OBJECTIVE

Whether the basal ganglia are involved in the cortical synchronization during focal seizures is still an open question. In the present study, we proposed to synchronize cortico-striatal activities acutely inducing striatal disinhibition, performing GABA-antagonist injections within the putamen in primates.

METHOD

Experiments were performed on three fascicularis monkeys. During each experimental session, low volumes of bicuculline (0.5-4 μL) were injected at a slow rate of 1 μL/min. Spontaneous behavioral changes were classified according to Racine's scale modified for primates. These induced motor behaviors were correlated with electromyographic, electroencephalographic, and putaminal and pallidal local field potentials changes in activity.

RESULTS

acute striatal desinhibition induced focal motor seizures. Seizures were closely linked to cortical epileptic activity synchronized with a striatal paroxysmal activity. These changes in striatal activity preceded the cortical epileptic activity and the induced myoclonia, and both cortical and subcortical activities were coherently synchronized during generalized seizures.

INTERPRETATION

Our results strongly suggest the role of the sensorimotor striatum in the regulation and synchronization of cortical excitability. These dramatic changes in the activity of this "gating" pathway might influence seizure susceptibility by modulating the threshold for the initiation of focal motor seizures.

Dissociating self-generated volition from externally-generated motivation

Insight into motivational processes may be gained by examining measures of willingness to exert effort for rewards, which have been linked to neuropsychiatric symptoms of anhedonia and apathy. However, while much work has focused on the development of models of motivation based on classic tasks of externally-generated levels of effort for reward, there has been less focus on the question of self-generated motivation or volition. We developed a task that aims to capture separate measures of self-generated and externally-generated motivation, with two task variants for physical and cognitive effort, and sought to test and validate this measure in two populations of healthy volunteers (N = 27 and N = 28). Similar to previous reports, a sigmoid function represented a better overall fit to the effort-reward data than a linear or Weibull model. Individual sigmoid function shapes were governed by two free parameters: bias (the amount of reward needed for effort initiation) and reward insensitivity (the amount of increase in reward needed to accelerate effort expenditure). For both physical and cognitive effort, bias was higher in the self-generated condition, indicating reduced self-generated volitional effort initiation, compared to externally-generated effort initiation, across effort domains. Bias against initial effort initiation in the self-generated condition was related to a specific dimensional measure of anticipatory anhedonia. For physical effort only, reward insensitivity was also higher in the self-generated condition compared to the externally-generated motivation condition, indicating lower self-generated effort acceleration. This work provides a novel objective measure of self-generated motivation that may provide insights into mechanisms of anhedonia and related symptoms.

The Pathophysiology of Tics; An Evolving Story

Background:

Tics, defined as quick, rapid, sudden, recurrent, non-rhythmic motor movements or vocalizations are required components of Tourette Syndrome (TS) - a complex disorder characterized by the presence of fluctuating, chronic motor and vocal tics, and the presence of co-existing neuropsychological problems. Despite many advances, the underlying pathophysiology of tics/TS remains unknown.

Objective:

To address a variety of controversies surrounding the pathophysiology of TS. More specifically: 1) the configuration of circuits likely involved; 2) the role of inhibitory influences on motor control; 3) the classification of tics as either goal-directed or habitual behaviors; 4) the potential anatomical site of origin, e.g. cortex, striatum, thalamus, cerebellum, or other(s); and 5) the role of specific neurotransmitters (dopamine, glutamate, GABA, and others) as possible mechanisms (Abstract figure).

Methods:

Existing evidence from current clinical, basic science, and animal model studies are reviewed to provide: 1) an expanded understanding of individual components and the complex integration of the Cortico-Basal Ganglia-Thalamo-Cortical (CBGTC) circuit - the pathway involved with motor control; and 2) scientific data directly addressing each of the aforementioned controversies regarding pathways, inhibition, classification, anatomy, and neurotransmitters.

Conclusion:

Until a definitive pathophysiological mechanism is identified, one functional approach is to consider that a disruption anywhere within CBGTC circuitry, or a brain region inputting to the motor circuit, can lead to an aberrant message arriving at the primary motor cortex and enabling a tic. Pharmacologic modulation may be therapeutically beneficial, even though it might not be directed toward the primary abnormality.

Clinical Features That Evoke the Concept of Disinhibition in Tourette Syndrome

The capacity to efficiently control motor output, by either refraining from prepotent actions or disengaging from ongoing motor behaviors, is necessary for our ability to thrive in a stimulus-rich and socially complex environment. Failure to engage in successful inhibitory motor control could lead to aberrant behaviors typified by an excess of motor performance. In tic disorders and Tourette syndrome (TS) - the most common tic disorder encountered in clinics - surplus motor output is rarely the only relevant clinical sign. A range of abnormal behaviors is often encountered which are historically viewed as "disinhibition phenomena". Here, we present the different clinical features of TS from distinct categorical domains (motor, sensory, complex behavioral) that evoke the concept of disinhibition and discuss their associations. We also present evidence for their consideration as phenomena of inhibitory dysfunction and provide an overview of studies on TS pathophysiology which support this view. We then critically dissect the concept of disinhibition in TS and illuminate other salient aspects, which should be considered in a unitary pathophysiological approach. We briefly touch upon the dangers of oversimplification and emphasize the necessity of conceptual diversity in the scientific exploration of TS, from disinhibition and beyond.

The anterior caudate nucleus supports impulsive choices triggered by pramipexole

BACKGROUND

Pramipexole is a dopamine agonist used as a treatment in PD and restless legs syndrome to reduce motor symptoms, but it often induces impulse control disorders. In particular, patients with impulse control disorders tend to make more impulsive choices in the delay discounting task, that is, they choose small immediate rewards over larger delayed ones more often than patients without impulse control disorders and healthy subjects do. Yet the site of action of pramipexole that produces these impulsive choices remains unknown. Based on the heterogeneity of corticostriatal projections and the massive dopamine innervation of the striatum, we hypothesized that impulsive choices triggered by dopamine treatments may be supported by a specific striatal territory.

OBJECTIVES

This study aims to determine by which anteriorstriatum territory the Pramipexole trigger impulsive choices; the caudate nucleus, the ventral striatum or the putamen.

METHODS

We compared pramipexole intramuscular injections to intracerebral microinjections within the three striatal territories in healthy monkeys trained to execute the delay discounting task, a behavioral paradigm typically used to evaluate impulsive choices.

RESULTS

We found that pramipexole intramuscular injections induced impulsive choices in all monkeys. Local microinjections were performed inside the anterior caudate nucleus, ventral striatum, and anterior putamen and reproduced those impulsive choices when pramipexole was directly injected into the caudate nucleus, whereas injections into the ventral striatum or putamen had no effect on monkeys' choices.

CONCLUSIONS

These results, consistent with clinical studies, suggest that impulsive choices triggered by pramipexole are supported by the caudate nucleus, allowing us to emphasize the importance of dopamine modulation inside this striatal territory in decision processes underlying impulsive behaviors. © 2019 International Parkinson and Movement Disorder Society.

Disinhibition of the Nucleus Accumbens Leads to Macro-Scale Hyperactivity Consisting of Micro-Scale Behavioral Segments Encoded by Striatal Activity

The striatum comprises of multiple functional territories involved with multilevel control of behavior. Disinhibition of different functional territories leads to territory-specific hyperkinetic and hyperbehavioral symptoms. The ventromedial striatum, including the nucleus accumbens (NAc) core, is typically associated with limbic input but was historically linked to high-level motor control. In this study, performed in female Long-Evans rats, we show that the NAc core directly controls motor behavior on multiple timescales. On the macro-scale, following NAc disinhibition, the animals manifested prolonged hyperactivity, expressed as excessive normal behavior, whereas on the micro-scale multiple behavior transitions occurred, generating short movement segments. The underlying striatal network displayed population-based local field potential transient deflections (LFP spikes) whose rate determined the magnitude of the hyperactivity and whose timing corresponded to unitary behavioral transition events. Individual striatal neurons preserved normal baseline activity and network interactions following the disinhibition, maintaining the normal encoding of behavioral primitives and forming a sparse link between the LFP spikes and single neuron activity. Disinhibition of this classically limbic territory leads to profound motor changes resembling hyperactivity and attention deficit. These behavioral and neuronal results highlight the direct interplay on multiple timescales between different striatal territories during normal and pathological conditions.SIGNIFICANCE STATEMENT The nucleus accumbens (NAc) is a key part of the striatal limbic territory. In the current study we show that this classically limbic area directly controls motor behavior on multiple timescales. Focal disinhibition of the NAc core in freely behaving rats led to macro-scale hyperactivity and micro-scale behavioral transitions, symptoms typically associated with attention deficit hyperactivity disorder. The behavioral changes were encoded by the striatal LFP signal and single-unit spiking activity in line with the neuronal changes observed during tic expression following disinhibition of the striatal motor territory. These results point to the need to extend the existing parallel functional pathway concept of basal ganglia function to include the study of limbic-motor cross-territory interactions in both health and disease.

Merging the Pathophysiology and Pharmacotherapy of Tics

Background

Anatomically, cortical-basal ganglia-thalamo-cortical (CBGTC) circuits have an essential role in the expression of tics. At the biochemical level, the proper conveyance of messages through these circuits requires several functionally integrated neurotransmitter systems. In this manuscript, evidence supporting proposed pathophysiological abnormalities, both anatomical and chemical is reviewed. In addition, the results of standard and emerging tic-suppressing therapies affecting nine separate neurotransmitter systems are discussed. The goal of this review is to integrate our current understanding of the pathophysiology of Tourette syndrome (TS) with present and proposed pharmacotherapies for tic suppression.

Methods

For this manuscript, literature searches were conducted for both current basic science and clinical information in PubMed, Google-Scholar, and other scholarly journals to September 2018.

Results

The precise primary site of abnormality for tics remains undetermined. Although many pathophysiologic hypotheses favor a specific abnormality of the cortex, striatum, or globus pallidus, others recognize essential influences from regions such as the thalamus, cerebellum, brainstem, and ventral striatum. Some prefer an alteration within direct and indirect pathways, whereas others believe this fails to recognize the multiple interactions within and between CBGTC circuits. Although research and clinical evidence supports involvement of the dopaminergic system, additional data emphasizes the potential roles for several other neurotransmitter systems.

Discussion

A greater understanding of the primary neurochemical defect in TS would be extremely valuable for the development of new tic-suppressing therapies. Nevertheless, recognizing the varied and complex interactions that exist in a multi-neurotransmitter system, successful therapy may not require direct targeting of the primary abnormality.

Deep Brain Stimulation for Refractory Obsessive-Compulsive Disorder: Towards an Individualized Approach

Obsessive-compulsive disorder (OCD) is a neuropsychiatric disorder featuring repetitive intrusive thoughts and behaviors associated with a significant handicap. Of patients, 20% are refractory to medication and cognitive behavioral therapy. Refractory OCD is associated with suicidal behavior and significant degradation of social and professional functioning, with high health costs. Deep brain stimulation (DBS) has been proposed as a reversible and controllable method to treat refractory patients, with meta-analyses showing 60% response rate following DBS, whatever the target: anterior limb of the internal capsule (ALIC), ventral capsule/ventral striatum (VC/VS), nucleus accumbens (NAcc), anteromedial subthalamic nucleus (amSTN), or inferior thalamic peduncle (ITP). But how do we choose the "best" target? Functional neuroimaging studies have shown that ALIC-DBS requires the modulation of the fiber tract within the ventral ALIC via the ventral striatum, bordering the bed nucleus of the stria terminalis and connecting the medial prefrontal cortex with the thalamus to be successful. VC/VS effective sites of stimulation were found within the VC and primarily connected to the medial orbitofrontal cortex (OFC) dorsomedial thalamus, amygdala, and the habenula. NAcc-DBS has been found to reduce OCD symptoms by decreasing excessive fronto-striatal connectivity between NAcc and the lateral and medial prefrontal cortex. The amSTN effective stimulation sites are located at the inferior medial border of the STN, primarily connected to lateral OFC, dorsal anterior cingulate, and dorsolateral prefrontal cortex. Finally, ITP-DBS recruits a bidirectional fiber pathway between the OFC and the thalamus. Thus, these functional connectivity studies show that the various DBS targets lie within the same diseased neural network. They share similar efficacy profiles on OCD symptoms as estimated on the Y-BOCS, the amSTN being the target supported by the strongest evidence in the literature. VC/VS-DBS, amSTN-DBS, and ALIC-DBS were also found to improve mood, behavioral adaptability and potentially both, respectively. Because OCD is such a heterogeneous disease with many different symptom dimensions, the ultimate aim should be to find the most appropriate DBS target for a given refractory patient. This quest will benefit from further investigation and understanding of the individual functional connectivity of OCD patients.

Tourette Syndrome as a Disorder of the Social Decision Making Network

Tourette syndrome is a common neurodevelopmental disorder defined by the presence of tics, stereotyped involuntary movements and phonations. Considerable evidence points to developmental abnormalities of the basal ganglia as tic substrates. Basal ganglia dysfunction does not account for important features of Tourette syndrome, including its natural history, male predominance, and the characteristic quality and distribution of tics. The latter mainly involve eye, face, and head movements, in addition to a variety of simple to complex phonations. A major normal function of these movements, and of phonations as well, is social signaling. Many important species- and sex-specific stereotyped social behaviors are mediated by a phylogenetically conserved network of subcortical nuclei, the social behavior network (SBN). Some SBN nuclei are sexually dimorphic, and SBN function is modulated strongly by gonadal steroids. Recent studies indicate that the SBN meshes with the basal ganglia to form a larger network, the Social Decision Making Network (SDM; O'Connell and Hofmann [2011]). The SDM concept overlaps significantly with Holstege's (1993) model of an emotional motor system mediating socially relevant facial movements and phonations. Dopaminergic signaling within the basal ganglia component of the SDM may regulate social act motivation with the SBN component responsible for act expression. Developmental SDM abnormalities can explain all major Tourette syndrome features, including natural history, male predominance, the characteristic distribution of tics, and their stereotyped quality. Some data directly support this hypothesis. Tourette syndrome may be a disorder of social communication manifesting primarily as abnormal involuntary movements.

Neuroscience of apathy and anhedonia: a transdiagnostic approach

Apathy and anhedonia are common syndromes of motivation that are associated with a wide range of brain disorders and have no established therapies. Research using animal models suggests that a useful framework for understanding motivated behaviour lies in effort-based decision making for reward. The neurobiological mechanisms underpinning such decisions have now begun to be determined in individuals with apathy or anhedonia, providing an important foundation for developing new treatments. The findings suggest that there might be some shared mechanisms between both syndromes. A transdiagnostic approach that cuts across traditional disease boundaries provides a potentially useful means for understanding these conditions.

Altered dopaminergic regulation of the dorsal striatum is able to induce tic-like movements in juvenile rats

Motor tics are sudden, repetitive, involuntary movements representing the hallmark behaviors of the neurodevelopmental disease Tourette’s syndrome (TS). The primary cause of TS remains unclear. The initial observation that dopaminergic antagonists alleviate tics led to the development of a dopaminergic theory of TS etiology which is supported by post mortem and in vivo studies indicating that non-physiological activation of the striatum could generate tics. The striatum controls movement execution through the balanced activity of dopamine receptor D1 and D2-expressing medium spiny neurons of the direct and indirect pathway, respectively. Different neurotransmitters can activate or repress striatal activity and among them, dopamine plays a major role. In this study we introduced a chronic dopaminergic alteration in juvenile rats, in order to modify the delicate balance between direct and indirect pathway. This manipulation was done in the dorsal striatum, that had been associated with tic-like movements generation in animal models. The results were movements resembling tics, which were categorized and scored according to a newly developed rating scale and were reduced by clonidine and riluzole treatment. Finally, post mortem analyses revealed altered RNA expression of dopaminergic receptors D1 and D2, suggesting an imbalanced dopaminergic regulation of medium spiny neuron activity as being causally related to the observed phenotype.

Altered anatomical connections of associative and limbic cortico-basal-ganglia circuits in obsessive-compulsive disorder

BACKGROUND

Current neurocognitive models suppose dysfunctions of associative and limbic cortico-basal ganglia circuits to be at the core of obsessive-compulsive disorder (OCD). As little is known about the state of underlying anatomical connections, we investigated whether these connections were reduced and/or not properly organised in OCD patients compared to control.

METHODS

Diffusion magnetic resonance images were obtained in 37 OCD patients with predominant checking symptoms and 37 matched healthy controls. We developed indices to characterise the quantity (spatial extent and density) and the organisation (topography and segregation) of 24 anatomical connections between associative and limbic cortical (anterior cingulate, dorsolateral prefrontal, orbitofrontal cortices and the frontal pole), and subcortical (caudate nucleus, putamen and thalamus) areas in each hemisphere.

RESULTS

Associative and limbic cortico-basal-ganglia connections were reduced in OCD patients compared to controls: 19/24 connections had a reduced subcortical spatial extent, 9/24 had a reduced density. Moreover, while the general topography was conserved, the different cortical projection fields in the striatum and thalamus were hyper-segregated in OCD patients compared to controls.

CONCLUSION

These quantitative and qualitative differences of anatomical connections go beyond the current model of a reduced cortical control of automatic behaviour stored in the basal ganglia. The hyper-segregation in OCD could also impair the integration of cortical information in the thalamus and striatum and distort the subsequent behavioural selection process. This provides new working hypotheses for functional and behavioural studies on OCD.

Pathophysiology of dyskinesia and behavioral disorders in non-human primates: the role of serotonergic fibers

The MPTP monkey model of Parkinson's disease (PD) has allowed huge advances regarding the understanding of the pathological mechanisms of PD and L-DOPA-induced adverse effects. Among the main findings were the imbalance between the efferent striatal pathways in opposite directions between the hypokinetic and hyperkinetic states of PD. In both normal and parkinsonian monkeys, the combination of behavioral and anatomical studies has allowed the deciphering of the cortico-basal ganglia circuits involved in both movement and behavioral disorders. A major breakthrough has then been made regarding the hypothesis of the involvement of serotonergic fibers in the conversion of L-DOPA to dopamine when dopaminergic neurons are dying and to release it, in an uncontrolled manner, as serotonergic neurons are deprived from the machinery required for buffering dopamine from the synaptic cleft. The crucial involvement of serotonergic fibers underlying L-DOPA-induced dyskinesia (LID) has been demonstrated in both rodent and monkey models of PD, in which dyskinesia induced by L-DOPA is abolished following lesion of the serotonergic system. Moreover, the role of serotonergic fibers goes well beyond dyskinesia, as lesioning of such serotonergic fibers by MDMA in the monkey also decreased other L-DOPA-induced adverse effects such as impulsive compulsive behaviors and visual hallucinations. The same pathological mechanism, i.e., an imbalance between serotonin and dopamine terminals may, therefore, favor L-DOPA-induced adverse effects according to the basal ganglia territory it inhabits. Further non-human primate studies will be needed to demonstrate the role of such a pathological mechanism in both movement and behavioral disorders driven by L-DOPA therapy but also to determine the causal link between serotonin lesions and the expression of non-motor symptoms like apathy, depression and anxiety, frequently observed in PD patients.

Aripiprazole Selectively Reduces Motor Tics in a Young Animal Model for Tourette's Syndrome and Comorbid Attention Deficit and Hyperactivity Disorder

Tourette’s syndrome (TS) is a neurodevelopmental disorder characterized primarily by motor and vocal tics. Comorbidities such as attention deficit and hyperactivity disorder (ADHD) are observed in over 50% of TS patients. We applied aripiprazole in a juvenile rat model that displays motor tics and hyperactivity. We additionally assessed the amount of ultrasonic vocalizations (USVs) as an indicator for the presence of vocal tics and evaluated the changes in the striatal neurometabolism using in vivo proton magnetic resonance spectroscopy (1H-MRS) at 11.7T. Thirty-one juvenile spontaneously hypertensive rats (SHRs) underwent bicuculline striatal microinjection and treatment with either aripiprazole or vehicle. Control groups were sham operated and sham injected. Behavior, USVs, and striatal neurochemical profile were analyzed at early, middle, and late adolescence (postnatal days 35 to 50). Bicuculline microinjections in the dorsolateral striatum induced motor tics in SHR juvenile rats. Acute aripiprazole administration selectively reduced both tic frequency and latency, whereas stereotypies, USVs, and hyperactivity remained unaltered. The striatal neurochemical profile was only moderately altered after tic-induction and was not affected by systemic drug treatment. When applied to a young rat model that provides high degrees of construct, face, and predictive validity for TS and comorbid ADHD, aripiprazole selectively reduces motor tics, revealing that tics and stereotypies are distinct phenomena in line with clinical treatment of patients. Finally, our 1H-MRS results suggest a critical revision of the striatal role in the hypothesized cortico-striatal dysregulation in TS pathophysiology.

The pathophysiological mechanisms of motivational deficits in Parkinson's disease

Parkinson's disease (PD) is a progressive degenerative disorder that leads to disabling motor symptoms and a wide variety of neuropsychiatric symptoms. Apathy is the most common psychiatric disorder in the early stages of untreated PD and can be defined as a hypodopaminergic syndrome, which also includes anxiety and depression. Apathy is also considered the core feature of the parkinsonian triad (apathy, anxiety and depression) of behavioural non-motor signs, including a motivational deficit. Moreover, apathy is recognised as a distinct chronic neuropsychiatric behavioural disorder based on specific diagnostic criteria. Given the prevalence of apathy in approximately 40% of the general Parkinson's disease population, this appears to be a contributing factor to dementia in PD; also, apathy symptoms are factors that potentially contribute to morbidity, leading to a major impairment of health-related quality of life, thus stressing the importance of understanding the pathophysiology of this disease. Several studies have clearly established a prominent role for DA-mediated signals in PD apathy. However, synergistic interaction between dopaminergic impairment resulting from the neurodegenerative process and deep brain stimulation of the subthalamic nucleus may cause or exacerbate apathy. Furthermore, serotoninergic mechanism signalling is also likely to be of importance in this pathophysiology.

Tourette syndrome: a disorder of the social decision-making network

Tourette syndrome is a common neurodevelopmental disorder defined by characteristic involuntary movements, tics, with both motor and phonic components. Tourette syndrome is usually conceptualized as a basal ganglia disorder, with an emphasis on striatal dysfunction. While considerable evidence is consistent with these concepts, imaging data suggest diffuse functional and structural abnormalities in Tourette syndrome brain. Tourette syndrome exhibits features that are difficult to explain solely based on basal ganglia circuit dysfunctions. These features include the natural history of tic expression, with typical onset of tics around ages 5 to 7 years and exacerbation during the peri-pubertal years, marked sex disparity with higher male prevalence, and the characteristic distribution of tics. The latter are usually repetitive, somewhat stereotyped involuntary eye, facial and head movements, and phonations. A major functional role of eye, face, and head movements is social signalling. Prior work in social neuroscience identified a phylogenetically conserved network of sexually dimorphic subcortical nuclei, the Social Behaviour Network, mediating many social behaviours. Social behaviour network function is modulated developmentally by gonadal steroids and social behaviour network outputs are stereotyped sex and species specific behaviours. In 2011 O'Connell and Hofmann proposed that the social behaviour network interdigitates with the basal ganglia to form a greater network, the social decision-making network. The social decision-making network may have two functionally complementary limbs: the basal ganglia component responsible for evaluation of socially relevant stimuli and actions with the social behaviour network component responsible for the performance of social acts. Social decision-making network dysfunction can explain major features of the neurobiology of Tourette syndrome. Tourette syndrome may be a disorder of social communication resulting from developmental abnormalities at several levels of the social decision-making network. The social decision-making network dysfunction hypothesis suggests new avenues for research in Tourette syndrome and new potential therapeutic targets.

Loss of Balance between Striatal Feedforward Inhibition and Corticostriatal Excitation Leads to Tremor

Fast-spiking interneurons (FSIs) exert powerful inhibitory control over the striatum and are hypothesized to balance the massive excitatory cortical and thalamic input to this structure. We recorded neuronal activity in the dorsolateral striatum and globus pallidus (GP) concurrently with the detailed movement kinematics of freely behaving female rats before and after selective inhibition of FSI activity using IEM-1460 microinjections. The inhibition led to the appearance of episodic rest tremor in the body part that depended on the somatotopic location of the injection within the striatum. The tremor was accompanied by coherent oscillations in the local field potential (LFP). Individual neuron activity patterns became oscillatory and coherent in the tremor frequency. Striatal neurons, but not GP neurons, displayed additional temporal, nonoscillatory correlations. The subsequent reduction in the corticostriatal input following muscimol injection to the corresponding somatotopic location in the primary motor cortex led to disruption of the tremor and a reduction of the LFP oscillations and individual neuron's phase-locked activity. The breakdown of the normal balance of excitation and inhibition in the striatum has been shown previously to be related to different motor abnormalities. Our results further indicate that the balance between excitatory corticostriatal input and feedforward FSI inhibition is sufficient to break down the striatal decorrelation process and generate oscillations resulting in rest tremor typical of multiple basal ganglia disorders.SIGNIFICANCE STATEMENT Fast-spiking interneurons (FSIs) play a key role in normal striatal processing by exerting powerful inhibitory control over the network. FSI malfunctions have been associated with abnormal processing of information within the striatum that leads to multiple movement disorders. Here, we study the changes in neuronal activity and movement kinematics following selective inhibition of these neurons. The injections led to the appearance of episodic rest tremor, accompanied by coherent oscillations in neuronal activity, which was reversed following corticostriatal inhibition. These results suggest that the balance between corticostriatal excitation and feedforward FSI inhibition is crucial for maintaining the striatal decorrelation process, and that its breakdown leads to the formation of oscillations resulting in rest tremor typical of multiple basal ganglia disorders.

Anterior pallidal deep brain stimulation for Tourette's syndrome: a randomised, double-blind, controlled trial

BACKGROUND

Deep brain stimulation (DBS) has been proposed to treat patients with severe Tourette's syndrome, and open-label trials and two small double-blind trials have tested DBS of the posterior and the anterior internal globus pallidus (aGPi). We aimed to specifically assess the efficacy of aGPi DBS for severe Tourette's syndrome.

METHODS

In this randomised, double-blind, controlled trial, we recruited patients aged 18-60 years with severe and medically refractory Tourette's syndrome from eight hospitals specialised in movement disorders in France. Enrolled patients received surgery to implant bilateral electrodes for aGPi DBS; 3 months later they were randomly assigned (1:1 ratio with a block size of eight; computer-generated pairwise randomisation according to order of enrolment) to receive either active or sham stimulation for the subsequent 3 months in a double-blind fashion. All patients then received open-label active stimulation for the subsequent 6 months. Patients and clinicians assessing outcomes were masked to treatment allocation; an unmasked clinician was responsible for stimulation parameter programming, with intensity set below the side-effect threshold. The primary endpoint was difference in Yale Global Tic Severity Scale (YGTSS) score between the beginning and end of the 3 month double-blind period, as assessed with a Mann-Whitney-Wilcoxon test in all randomly allocated patients who received active or sham stimulation during the double-blind period. We assessed safety in all patients who were enrolled and received surgery for aGPi DBS. This trial is registered with ClinicalTrials.gov, number NCT00478842.

FINDINGS

Between Dec 6, 2007, and Dec 13, 2012, we enrolled 19 patients. We randomly assigned 17 (89%) patients, with 16 completing blinded assessments (seven [44%] in the active stimulation group and nine [56%] in the sham stimulation group). We noted no significant difference in YGTSS score change between the beginning and the end of the 3 month double-blind period between groups (active group median YGTSS score 68·5 [IQR 34·0 to 83·5] at the beginning and 62·5 [51·5 to 72·0] at the end, median change 1·1% [IQR -23·9 to 38·1]; sham group 73·0 [69·0 to 79·0] and 79·0 [59·0 to 81·5], median change 0·0% [-10·6 to 4·8]; p=0·39). 15 serious adverse events (three in patients who withdrew before stimulation and six each in the active and sham stimulation groups) occurred in 13 patients (three who withdrew before randomisation, four in the active group, and six in the sham group), with infections in DBS hardware in four patients (two who withdrew before randomisation, one in the sham stimulation group, and one in the active stimulation group). Other serious adverse events included one electrode misplacement (active stimulation group), one episode of depressive signs (active stimulation group), and three episodes of increased tic severity and anxiety (two in the sham stimulation group and one in the active stimulation group).

INTERPRETATION

3 months of aGPi DBS is insufficient to decrease tic severity for patients with Tourette's syndrome. Future research is needed to investigate the efficacy of aGPi DBS for patients over longer periods with optimal stimulation parameters and to identify potential predictors of the therapeutic response.

FUNDING

French Ministry of Health.

Ventral Pallidum Encodes Contextual Information and Controls Aversive Behaviors

Successful avoidance of aversive outcomes is crucial for the survival of animals. Although accumulating evidence indicates that an indirect pathway in the basal ganglia is involved in aversive behavior, the ventral pallidum (VP), which is an important component of this pathway, has so far been implicated primarily in appetitive behavior. In this study, we used single-cell recordings and bicuculline (GABAA antagonist) injections to elucidate the role of VP both in the encoding of aversive context and in active avoidance. We found 2 populations of neurons that were preferentially activated by appetitive and aversive conditioned stimuli (CSs). In addition, VP showed appetitive and aversive outcome anticipatory activities. These activity patterns indicate that VP is involved in encoding and maintaining CS-induced aversive contextual information. Furthermore, the disturbance of VP activity by bicuculline injection increased the number of error trials in aversive trials. In particular, the subjects released the response bar prematurely, showed no response at all, or failed to avoid the aversive outcome. Overall, these results suggest that VP plays a central role in controlling CS-induced negative motivation to produce avoidance behavior.

Dysfunctions of the basal ganglia-cerebellar-thalamo-cortical system produce motor tics in Tourette syndrome

Motor tics are a cardinal feature of Tourette syndrome and are traditionally associated with an excess of striatal dopamine in the basal ganglia. Recent evidence increasingly supports a more articulated view where cerebellum and cortex, working closely in concert with basal ganglia, are also involved in tic production. Building on such evidence, this article proposes a computational model of the basal ganglia-cerebellar-thalamo-cortical system to study how motor tics are generated in Tourette syndrome. In particular, the model: (i) reproduces the main results of recent experiments about the involvement of the basal ganglia-cerebellar-thalamo-cortical system in tic generation; (ii) suggests an explanation of the system-level mechanisms underlying motor tic production: in this respect, the model predicts that the interplay between dopaminergic signal and cortical activity contributes to triggering the tic event and that the recently discovered basal ganglia-cerebellar anatomical pathway may support the involvement of the cerebellum in tic production; (iii) furnishes predictions on the amount of tics generated when striatal dopamine increases and when the cortex is externally stimulated. These predictions could be important in identifying new brain target areas for future therapies. Finally, the model represents the first computational attempt to study the role of the recently discovered basal ganglia-cerebellar anatomical links. Studying this non-cortex-mediated basal ganglia-cerebellar interaction could radically change our perspective about how these areas interact with each other and with the cortex. Overall, the model also shows the utility of casting Tourette syndrome within a system-level perspective rather than viewing it as related to the dysfunction of a single brain area.

Tourette syndrome is a neuropsychiatric disorder characterized by vocal and motor tics. Tics represent a cardinal symptom traditionally associated with a dysfunction of the basal ganglia leading to an excess of the dopamine neurotransmitter. This view gives a restricted clinical picture and limits therapeutic approaches because it ignores the influence of altered interactions between the basal ganglia and other brain areas. In this respect, recent evidence supports a more articulated framework where cerebellum and cortex are also involved in tic production. Building on these data, we propose a computational model of the basal ganglia-cerebellar-thalamo-cortical network to investigate the specific mechanisms underlying motor tic production. The model reproduces the results of recent experiments and suggests an explanation of the system-level processes underlying tic production. Moreover, it furnishes predictions related to the amount of tics generated when there are dysfunctions in the basal ganglia-cerebellar-thalamo-cortical circuits. These predictions could be important in identifying new brain target areas for future therapies based on a system-level view of Tourette syndrome.

Prolonged striatal disinhibition as a chronic animal model of tic disorders

BACKGROUND

Experimental findings and theoretical models have associated Tourette syndrome with abnormal striatal inhibition. The expression of tics, the hallmark symptom of this disorder, has been transiently induced in non-human primates and rodents by the injection of GABA_A antagonists into the striatum, leading to temporary disinhibition.

NEW METHOD

The novel chronic model of tic expression utilizes mini-osmotic pumps implanted subcutaneously in the rat's back for prolonged infusion of bicuculline into the dorsolateral striatum.

RESULTS

Tics were expressed on the contralateral side to the infusion over a period of multiple days. Tic expression was stable, and maintained similar properties throughout the infusion period. Electrophysiological recordings revealed the existence of tic-related local field potential spikes and individual neuron activity changes that remained stable throughout the infusion period.

COMPARISON WITH EXISTING METHODS

The striatal disinhibition model provides a unique combination of face validity (tic expression) and construct validity (abnormal striatal inhibition) but is limited to sub-hour periods. The new chronic model extends the period of tic expression to multiple days and thus enables the study of tic dynamics and the effects of behavior and pharmacological agents on tic expression.

CONCLUSIONS

The chronic model provides similar behavioral and neuronal correlates of tics as the acute striatal disinhibition model but over prolonged periods of time, thus providing a unique, basal ganglia initiated model of tic expression. Chronic expression of symptoms is the key to studying the time varying properties of Tourette syndrome and the effects of multiple internal and external factors on this disorder.

Dopamine and serotonin modulation of motor and non-motor functions of the non-human primate striato-pallidal circuits in normal and pathological states

Thanks to the non-human primate (NHP), we have shown that the pharmacological disturbance of the anterior striatum or of external globus pallidus triggers a set of motivation and movement disorders, depending on the functional subterritory involved. One can, therefore, assume that the aberrant activity of the different subterritories of basal ganglia (BG) could lead to different behavioral disorders in neuropsychiatric disorders as Tourette's syndrome and Parkinson's disease. We are now addressing in the NHP the impact of modulating dopamine or serotonin within the BG on behavioral disorders. Indeed, we have shown a prominent role of serotonergic degeneration within the ventral striatum and caudate nucleus in neuropsychiatric symptoms in de novo PD patients. Of note, the serotonergic modulation of these BG regions in the NHP plays also a critical role in the induction or treatment of behavioral disorders. Given that both dopamine and serotonin are targeted to treat neuropsychiatric disorders, we are studying the effects of modulating dopamine and serotonin transporters in the different territories of the striatum, and more particularly within the ventral striatum on decision-making processing at both behavioral and neuronal levels. Finally, we evidence the need to extend the pharmacological approach to the receptors of these two neuromodulator systems as the use of substances targeting receptor subtypes preferentially localized in the associative and limbic territories of BG could be very effective to specifically improve the behavioral disorders in Parkinson's disease, Gilles de la Tourette syndrome but also in several psychiatric disorders such as depression, anxiety, anorexia, or impulse control disorders.

Parallel basal ganglia circuits for decision making

The basal ganglia control body movements, mainly, based on their values. Critical for this mechanism is dopamine neurons, which sends unpredicted value signals, mainly, to the striatum. This mechanism enables animals to change their behaviors flexibly, eventually choosing a valuable behavior. However, this may not be the best behavior, because the flexible choice is focused on recent, and, therefore, limited, experiences (i.e., short-term memories). Our old and recent studies suggest that the basal ganglia contain separate circuits that process value signals in a completely different manner. They are insensitive to recent changes in value, yet gradually accumulate the value of each behavior (i.e., movement or object choice). These stable circuits eventually encode values of many behaviors and then retain the value signals for a long time (i.e., long-term memories). They are innervated by a separate group of dopamine neurons that retain value signals, even when no reward is predicted. Importantly, the stable circuits can control motor behaviors (e.g., hand or eye) quickly and precisely, which allows animals to automatically acquire valuable outcomes based on historical life experiences. These behaviors would be called 'skills', which are crucial for survival. The stable circuits are localized in the posterior part of the basal ganglia, separately from the flexible circuits located in the anterior part. To summarize, the flexible and stable circuits in the basal ganglia, working together but independently, enable animals (and humans) to reach valuable goals in various contexts.

Addressing the Complexity of Tourette's Syndrome through the Use of Animal Models

Tourette's syndrome (TS) is a neurodevelopmental disorder characterized by fluctuating motor and vocal tics, usually preceded by sensory premonitions, called premonitory urges. Besides tics, the vast majority—up to 90%—of TS patients suffer from psychiatric comorbidities, mainly attention deficit/hyperactivity disorder (ADHD) and obsessive-compulsive disorder (OCD). The etiology of TS remains elusive. Genetics is believed to play an important role, but it is clear that other factors contribute to TS, possibly altering brain functioning and architecture during a sensitive phase of neural development. Clinical brain imaging and genetic studies have contributed to elucidate TS pathophysiology and disease mechanisms; however, TS disease etiology still is poorly understood. Findings from genetic studies led to the development of genetic animal models, but they poorly reflect the pathophysiology of TS. Addressing the role of neurotransmission, brain regions, and brain circuits in TS disease pathomechanisms is another focus area for preclinical TS model development. We are now in an interesting moment in time when numerous innovative animal models are continuously brought to the attention of the public. Due to the diverse and largely unknown etiology of TS, there is no single preclinical model featuring all different aspects of TS symptomatology. TS has been dissected into its key symptomst hat have been investigated separately, in line with the Research Domain Criteria concept. The different rationales used to develop the respective animal models are critically reviewed, to discuss the potential of the contribution of animal models to elucidate TS disease mechanisms.