Intact automatic motor inhibition in patients with tourette syndrome

Rapid Compensation for Noisy Voluntary Movements in Adults with Primary Tic Disorders

BACKGROUND

It has been proposed that tics and premonitory urges in primary tic disorders (PTD), like Tourette syndrome, are a manifestation of sensorimotor noise. However, patients with tics show no obvious movement imprecision in everyday life. One reason could be that patients have strategies to compensate for noise that disrupts performance (ie, noise that is task-relevant).

OBJECTIVES

Our goal was to unmask effects of elevated sensorimotor noise on the variability of voluntary movements in patients with PTD.

METHODS

We tested 30 adult patients with PTD (23 male) and 30 matched controls in a reaching task designed to unmask latent noise. Subjects reached to targets whose shape allowed for variability either in movement direction or extent. This enabled us to decompose variability into task-relevant versus less task-relevant components, where the latter should be less affected by compensatory strategies than the former. In alternating blocks, the task-relevant target dimension switched, allowing us to explore the temporal dynamics with which participants adjusted movement variability to changes in task demands.

RESULTS

Both groups accurately reached to targets, and adjusted movement precision based on target shape. However, when task-relevant dimensions of the target changed, patients initially produced movements that were more variable than controls, before regaining precision after several reaches. This effect persisted across repeated changes in the task-relevant dimension across the experiment, and therefore did not reflect an effect of novelty, or differences in learning.

CONCLUSIONS

Our results suggest that patients with PTD generate noisier voluntary movements compared with controls, but rapidly compensate according to current task demands. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

A double-blind, sham-controlled, trial of home-administered rhythmic 10-Hz median nerve stimulation for the reduction of tics, and suppression of the urge-to-tic, in individuals with Tourette syndrome and chronic tic disorder

Tourette syndrome (TS) and chronic tic disorder (CTD) are neurological disorders of childhood onset characterized by the occurrence of tics; repetitive, purposeless, movements or vocalizations of short duration which can occur many times throughout a day. Currently, effective treatment for tic disorders is an area of considerable unmet clinical need. We aimed to evaluate the efficacy of a home-administered neuromodulation treatment for tics involving the delivery of rhythmic pulse trains of median nerve stimulation (MNS) delivered via a wearable 'watch-like' device worn at the wrist. We conducted a UK-wide parallel double-blind sham-controlled trial for the reduction of tics in individuals with tic disorder. The device was programmed to deliver rhythmic (10 Hz) trains of low-intensity (1-19 mA) electrical stimulation to the median nerve for a pre-determined duration each day, and was intended to be used by each participant in their home once each day, 5 days each week, for a period of 4 weeks. Between 18th March 2022 and 26th September 2022, 135 participants (45 per group) were initially allocated, using stratified randomization, to one of the following groups; active stimulation; sham stimulation or to a waitlist (i.e. treatment as usual) control group. Recruited participants were individuals with confirmed or suspected TS/CTD aged 12 years of age or upward with moderate to severe tics. Researchers involved in the collection or processing of measurement outcomes and assessing the outcomes, as well as participants in the active and sham groups and their legal guardians were all blind to the group allocation. The primary outcome measure used to assess the 'offline' or treatment effect of stimulation was the Yale Global Tic Severity Scale-Total Tic Severity Score (YGTSS-TTSS) assessed at the conclusion of 4 weeks of stimulation. The primary outcome measure used to assess the 'online' effects of stimulation was tic frequency, measured as the number of tics per minute (TPM) observed, based upon blind analysis of daily video recordings obtained while stimulation was delivered. The results demonstrated that after 4-week stimulation, tic severity (YGTSS-TTSS) had reduced by 7.1 points (35 percentile reduction) for the active stimulation group compared to 2.13/2.11 points for the sham stimulation and waitlist control groups. The reduction in YGTSS-TTSS for the active stimulation group was substantially larger, clinically meaningful (effect size = .5) and statistically significant (p = .02) compared to both the sham stimulation and waitlist control groups, which did not differ from one another (effect size = -.03). Furthermore, blind analyses of video recordings demonstrated that tic frequency (tics per minute) reduced substantially (-15.6 TPM) during active stimulation compared to sham stimulation (-7.7 TPM). This difference represents a statistically significant (p < .03) and clinically meaningful reduction in tic frequency (>25 percentile reduction: effect size = .3). These findings indicate that home-administered rhythmic MNS delivered through a wearable wrist-worn device has the potential to be an effective community-based treatment for tic disorders.

EEG Correlates of Active Stopping and Preparation for Stopping in Chronic Tic Disorder

Motor inhibition is an important cognitive process involved in tic suppression. As the right frontal lobe contains important inhibitory network nodes, we characterized right superior, middle, and inferior frontal gyral (RSFG, RMFG, RIFG) event-related oscillations during motor inhibition in youth with chronic tic disorders (CTD) versus controls. Fourteen children with CTD and 13 controls (10–17 years old) completed an anticipated-response stop signal task while dense-array electroencephalography was recorded. Between-group differences in spectral power changes (3–50 Hz) were explored after source localization and multiple comparisons correction. Two epochs within the stop signal task were studied: (1) preparatory phase early in the trial before motor execution/inhibition and (2) active inhibition phase after stop signal presentation. Correlation analyses between electrophysiologic data and clinical rating scales for tic, obsessive-compulsive symptoms, and inattention/hyperactivity were performed. There were no behavioral or electrophysiological differences during active stopping. During stop preparation, CTD participants showed greater event-related desynchronization (ERD) in the RSFG (γ-band), RMFG (β, γ-bands), and RIFG (θ, α, β, γ-bands). Higher RSFG γ-ERD correlated with lower tic severity (r = 0.66, p = 0.04). Our findings suggest RSFG γ-ERD may represent a mechanism that allows CTD patients to keep tics under control and achieve behavioral performance similar to peers.

Correlates and clinical implications of tic suppressibility

Purpose of review

Tic disorders are common in the pediatric population and are differentiated from other movement disorders by tic suppressibility. Understanding the mechanism of tic suppression may provide new insights to the pathophysiology of tic disorders. This article highlights clinical phenomenology and neuronal correlates of tic suppressibility.

Recent findings

Recent studies suggest that tic suppressibility exists in children shortly after onset of their tics. Moreover, those who are better able to suppress their tics have better tic outcomes. Interoceptive awareness and automatic action inhibition may be involved in tic suppression.

Summary

We illustrate a possible underlying mechanism of tic suppressibility and its clinical correlations and implications. New concepts such as interoceptive awareness and action inhibition may help explain tic disorders. Further study will be useful to fill remaining knowledge gaps.

Non-invasive Brain Stimulation for the Treatment of Gilles de la Tourette Syndrome

Gilles de la Tourette Syndrome is a multifaceted neuropsychiatric disorder typically commencing in childhood and characterized by motor and phonic tics. Its pathophysiology is still incompletely understood. However, there is convincing evidence that structural and functional abnormalities in the basal ganglia, in cortico-striato-thalamo-cortical circuits, and some cortical areas including medial frontal regions and the prefrontal cortex as well as hyperactivity of the dopaminergic system are key findings. Conventional therapeutic approaches in addition to counseling comprise behavioral treatment, particularly habit reversal therapy, oral pharmacotherapy (antipsychotic medication, alpha-2-agonists) and botulinum toxin injections. In treatment-refractory Tourette syndrome, deep brain stimulation, particularly of the internal segment of the globus pallidus, is an option for a small minority of patients. Based on pathophysiological considerations, non-invasive brain stimulation might be a suitable alternative. Repetitive transcranial magnetic stimulation appears particularly attractive. It can lead to longer-lasting alterations of excitability and connectivity in cortical networks and inter-connected regions including the basal ganglia through the induction of neural plasticity. Stimulation of the primary motor and premotor cortex has so far not been shown to be clinically effective. Some studies, though, suggest that the supplementary motor area or the temporo-parietal junction might be more appropriate targets. In this manuscript, we will review the evidence for the usefulness of repetitive transcranial magnetic stimulation and transcranial electric stimulation as treatment options in Tourette syndrome. Based on pathophysiological considerations we will discuss the rational for other approaches of non-invasive brain stimulation including state informed repetitive transcranial magnetic stimulation.

Impaired automatic but intact volitional inhibition in primary tic disorders

The defining character of tics is that they can be transiently suppressed by volitional effort of will, and at a behavioural level this has led to the concept that tics result from a failure of inhibition. However, this logic conflates the mechanism responsible for the production of tics with that used in suppressing them. Volitional inhibition of motor output could be increased to prevent the tic from reaching the threshold for expression, although this has been extensively investigated with conflicting results. Alternatively, automatic inhibition could prevent the initial excitation of the striatal tic focus-a hypothesis we have previously introduced. To reconcile these competing hypotheses, we examined different types of motor inhibition in a group of 19 patients with primary tic disorders and 15 healthy volunteers. We probed proactive and reactive inhibition using the conditional stop-signal task, and applied transcranial magnetic stimulation to the motor cortex, to assess movement preparation and execution. We assessed automatic motor inhibition with the masked priming task. We found that volitional movement preparation, execution and inhibition (proactive and reactive) were not impaired in tic disorders. We speculate that these mechanisms are recruited during volitional tic suppression, and that they prevent expression of the tic by inhibiting the nascent excitation released by the tic generator. In contrast, automatic inhibition was abnormal/impaired in patients with tic disorders. In the masked priming task, positive and negative compatibility effects were found for healthy controls, whereas patients with tics exhibited strong positive compatibility effects, but no negative compatibility effect indicative of impaired automatic inhibition. Patients also made more errors on the masked priming task than healthy control subjects and the types of errors were consistent with impaired automatic inhibition. Errors associated with impaired automatic inhibition were positively correlated with tic severity. We conclude that voluntary movement preparation/generation and volitional inhibition are normal in tic disorders, whereas automatic inhibition is impaired-a deficit that correlated with tic severity and thus may constitute a potential mechanism by which tics are generated.

Loss in grey matter in a small network of brain areas underpins poor reactive inhibition in Obsessive-Compulsive Disorder patients

Reactive inhibition correlates with the severity of symptoms in paediatric patients with Obsessive-Compulsive Disorder (OCD) though not in those with Tourette syndrome (TS). Here we assessed whether structural alterations in both grey (GM) and white matter (WM) volumes correlate with a measure of reactive inhibition, i.e. the stop-signal reaction time (SSRT), and with clinical scale scores. Nine OCD and 11 TS uncomplicated drug-naïve paediatric patients and 12 age-matched controls underwent 3T magnetic resonance imaging scanning. Between-group differences in GM and WM volumes across the whole brain were assessed. Outside the scanner, patients performed a reaching version of the stop-signal task. Both behavioural inhibitory control and neuroimaging measures were normal in TS patients. By contrast, OCD patients exhibited a significant loss in GM volume in five areas. The GM volume of the left inferior frontal gyrus was inversely correlated with the length of the SSRT, the left mid-cingulate gyrus and the right middle frontal gyrus were inversely correlated with the severity of OCD symptoms, and the left insula and the right medial orbitofrontal gyrus were inversely correlated with both. These results indicate that cortical areas showing GM loss in OCD patients are also involved in the network subserving reactive inhibition.

Controversies Surrounding the Pathophysiology of Tics

Tics are sudden, rapid, recurrent, nonrhythmic motor movements or vocalizations (phonic productions) that are commonly present in children and are required symptoms for the diagnosis of Tourette syndrome. Despite their frequency, the underlying pathophysiology of tics/Tourette syndrome remains unknown. In this review, we discuss a variety of controversies surrounding the pathophysiology of tics, including the following: Are tics voluntary or involuntary? What is the role of the premonitory urge? Are tics due to excess excitatory or deficient inhibition? Is it time to adopt the contemporary version of the cortico-basal ganglia-thalamocortical (CBGTC) circuit? and Do we know the primary abnormal neurotransmitter in Tourette syndrome? Data from convergent clinical and animal model studies support complex interactions among the various CBGTC sites and neurotransmitters. Advances are being made; however, numerous pathophysiologic questions persist.

Tourette syndrome research highlights from 2018

This is the fifth yearly article in the Tourette Syndrome Research Highlights series, summarizing research from 2018 relevant to Tourette syndrome and other tic disorders. The authors briefly summarize reports they consider most important or interesting. The  highlights from 2019 article is being drafted on the Authorea online authoring platform, and readers are encouraged to add references or give feedback on our selections using the comments feature on that page. After the calendar year ends, the article is submitted as the annual update for the  Tics collection on F1000Research.