Clinical Features That Evoke the Concept of Disinhibition in Tourette Syndrome

Aberrant Functional Connectivity of the Salience Network in Adult Patients with Tic Disorders: A Resting-State fMRI Study

Tic disorders (TD) are characterized by the presence of motor and/or vocal tics. Common neurophysiological frameworks suggest dysregulations of the cortico-striatal-thalamo-cortical (CSTC) brain circuit that controls movement execution. Besides common tics, there are other "non-tic" symptoms that are primarily related to sensory perception, sensorimotor integration, attention, and social cognition. The existence of these symptoms, the sensory tic triggers, and the modifying effect of attention and cognitive control mechanisms on tics may indicate the salience network's (SN) involvement in the neurophysiology of TD. Resting-state functional MRI measurements were performed in 26 participants with TD and 25 healthy controls (HC). The group differences in resting-state functional connectivity patterns were measured based on seed-to-voxel connectivity analyses. Compared to HC, patients with TD exhibited altered connectivity between the core regions of the SN (insula, anterior cingulate cortex, and temporoparietal junction) and sensory, associative, and motor-related cortices. Furthermore, connectivity changes were observed in relation to the severity of tics in the TD group. The SN, particularly the insula, is likely to be an important site of dysregulation in TD. Our results provide evidence for large-scale neural deviations in TD beyond the CSTC pathologies. These findings may be relevant for developing treatment targets.

Evidence for a dissociation between moral reasoning and moral decision-making in Tourette syndrome

Despite the growing interest on how Tourette syndrome (TS) affects social cognition skills, this field remains to date relatively under-explored. Here, we aim to advance knowledge on the topic by studying moral decision-making and moral reasoning in a group of adolescents with TS and a group of healthy controls. Overall, we found higher endorsement (i.e. a greater 'yes' response rate) for utilitarian solutions of incidental and instrumental moral dilemmas in TS compared to controls. By contrast, we reported an overall higher tendency of TS individuals to apply principles described in the moral foundation questionnaire to establish whether something is morally right or wrong. Our results document intact moral reasoning in TS and suggest that a deficit in suppressing inappropriate behaviours and/or altered sense of agency might be responsible for their higher utilitarian moral decision-making.

Disinhibition Is an Essential Network Motif Coordinated by GABA Levels and GABA B Receptors

Network dynamics are crucial for action and sensation. Changes in synaptic physiology lead to the reorganization of local microcircuits. Consequently, the functional state of the network impacts the output signal depending on the firing patterns of its units. Networks exhibit steady states in which neurons show various activities, producing many networks with diverse properties. Transitions between network states determine the output signal generated and its functional results. The temporal dynamics of excitation/inhibition allow a shift between states in an operational network. Therefore, a process capable of modulating the dynamics of excitation/inhibition may be functionally important. This process is known as disinhibition. In this review, we describe the effect of GABA levels and GABAB receptors on tonic inhibition, which causes changes (due to disinhibition) in network dynamics, leading to synchronous functional oscillations.

Myoclonus and other jerky movement disorders

Myoclonus and other jerky movements form a large heterogeneous group of disorders. Clinical neurophysiology studies can have an important contribution to support diagnosis but also to gain insight in the pathophysiology of different kind of jerks. This review focuses on myoclonus, tics, startle disorders, restless legs syndrome, and periodic leg movements during sleep. Myoclonus is defined as brief, shock-like movements, and subtypes can be classified based the anatomical origin. Both the clinical phenotype and the neurophysiological tests support this classification: cortical, cortical-subcortical, subcortical/non-segmental, segmental, peripheral, and functional jerks. The most important techniques used are polymyography and the combination of electromyography-electroencephalography focused on jerk-locked back-averaging, cortico-muscular coherence, and the Bereitschaftspotential. Clinically, the differential diagnosis of myoclonus includes tics, and this diagnosis is mainly based on the history with premonitory urges and the ability to suppress the tic. Electrophysiological tests are mainly applied in a research setting and include the Bereitschaftspotential, local field potentials, transcranial magnetic stimulation, and pre-pulse inhibition. Jerks due to a startling stimulus form the group of startle syndromes. This group includes disorders with an exaggerated startle reflex, such as hyperekplexia and stiff person syndrome, but also neuropsychiatric and stimulus-induced disorders. For these disorders polymyography combined with a startling stimulus can be useful to determine the pattern of muscle activation and thus the diagnosis. Assessment of symptoms in restless legs syndrome and periodic leg movements during sleep can be performed with different validated scoring criteria with the help of electromyography.

Tourette syndrome research highlights from 2020

We present here research from 2020 relevant to Tourette syndrome (TS). The authors briefly summarize a few reports they consider most important or interesting.

Inhibitory Control in Children with Tourette Syndrome Is Impaired in Everyday Life but Intact during a Stop Signal Task

Tourette Syndrome (TS) has previously been associated with deficits in inhibitory control (IC). However, studies on IC in individuals with TS have produced conflicting results. In the present study, we investigated IC, comparing the Stop Signal Reaction Time (SSRT) measure with parent and teacher ratings of daily life IC in 169 children aged 8–12 (60 with TS, 60 typically developing controls, 27 with attention-deficit/hyperactivity disorder (ADHD), and 22 with TS + ADHD). We further investigated associations of IC with TS and ADHD symptom severity. Children with TS showed intact SSRT performance, but impairments in daily life IC, as reported by parents and teachers. For the latter, we observed a staircase distribution of groups, with the healthy controls presenting with the best IC, followed by TS, TS + ADHD, and finally ADHD. Dimensional analyses indicated a strong association between ADHD severity and both measures of IC. Our results indicate that children with TS are not impaired in a laboratory-based measure of IC, although some difficulties were evident from measures of everyday behaviour, which may in part be due to parents and teachers interpreting tics as disinhibited behaviour. Comorbid ADHD or the severity of subthreshold ADHD symptomatology appeared to account for IC deficits.

Cortical and Subcortical Brain Volumes Partially Mediate the Association between Dietary Composition and Behavioral Disinhibition: A UK Biobank Study

Behavioral disinhibition is observed to be an important characteristic of many neurodevelopmental and psychiatric disorders. Recent studies have linked dietary quality to levels of behavioral inhibition. However, it is currently unclear whether brain factors might mediate this. The current study investigates whether cortical and subcortical brain volumes mediate part of the association between dietary composition and behavioral disinhibition. A total of 15,258 subjects from the UK Biobank project were included in the current study. Dietary composition and behavioral disinhibition were based on Principle Component Analyses of self-reported dietary composition). As a further data reduction step, cortical and subcortical volume segmentations were input into an Independent Component Analysis. The resulting four components were used as mediator variables in the main mediation analyses, where behavioral disinhibition served as the outcome variable and dietary components as predictors. Our results show: (1) significant associations between all dietary components and brain volume components; (2) brain volumes are associated with behavioral disinhibition; (3) the mediation models show that part of the variance in behavioral disinhibition explained by dietary components (for healthy diet, restricted diet, and high-fat dairy diet) is mediated through the frontal-temporal/parietal brain volume component. These results are in part confirming our hypotheses and offer a first insight into the underlying mechanisms linking dietary composition, frontal-parietal brain volume, and behavioral disinhibition in the general adult population.

Self-injurious behavior in Tourette syndrome

INTRODUCTION

Tourette syndrome (TS) is characterized by the presence of motor and phonic tics, as well as a variety of behavioral co-morbidities. Self-injurious behavior (SIB) is one of the most serious manifestations of TS, but its pathophysiology is poorly understood.

METHODS

Consecutive patients with TS studied in a tertiary care center.

RESULTS

We identified a total of 34 patients (16.9%) with SIB from a cohort of 201 patients with TS. Most of these patients (n = 23, 11.4%) experienced self-directed damage; while others had outward-directed (n = 7, 3.5%) or tic-related SIB (n = 4, 2%). Compared to other patients with TS, those who manifested SIB (self- and outward-directed damage) were more likely to have tics involving shoulder (P = 0.046), trunk (P = 0.006), and arm (P = 0.017); as well as dystonic tics (P = 0.016); complex motor tics (P < 0.001), copropraxia (P = 0.045), complex phonic tics (P = 0.003), higher number of phonic tics (P = 0.001), verbalizations (P = 0.001), coprolalia (P = 0.006) and obsessive compulsive disorder (OCD) (P < 0.001) as determined by bivariate analysis. In the multivariate analysis only complex motor tics (P = 0.006), obsessive-compulsive behavior (P = 0.025) and greater severity of tics (P = 0.002) showed a statistically significant association with SIB. Patients with SIB had a greater probability of being selected for deep brain stimulation (DBS) therapy by the treating clinician (P = 0.01).

CONCLUSIONS

SIB is observed in about 17% of patients with TS. The presence of complex motor tics, OCD and greater severity of tics was related to the presence of SIB.

Inhibitory Control Deficits in Children with Tic Disorders Revealed by Object-Hit-and-Avoid Task

Background

Tic disorders may reflect impaired inhibitory control. This has been evaluated using different behavioural tasks, yielding mixed results. Our objective was to test inhibitory control in children with tics through simultaneous presentation of multiple, mobile stimuli.

Methods

Sixty-four children with tics (mean age 12.4 years; 7.5-18.5) were evaluated using a validated robotic bimanual exoskeleton protocol (Kinarm) in an object-hit-and-avoid task, in which target and distractor objects moved across a screen and participants aimed to hit only the targets while avoiding distractors. Performance was compared to 146 typically developing controls (mean age 13 years; 6.1-19.9). The primary outcome was the percentage of distractors struck.

Results

ANCOVA (age as covariate) showed participants struck significantly more distractors (participants without comorbid ADHD, 22.71% [SE 1.47]; participants with comorbid ADHD, 23.56% [1.47]; and controls, 15.59% [0.68]). Participants with comorbid ADHD struck significantly fewer targets (119.74 [2.77]) than controls, but no difference was found between participants without comorbid ADHD (122.66 [2.77]) and controls (127.00 [1.28]). Participants and controls did not differ significantly in movement speed and movement area. Just over 20% of participants with tics fell below the age-predicted norm in striking distractors, whereas fewer than 10% fell outside age-predicted norms in other task parameters.

Conclusions

In children with tics (without comorbid ADHD), acting upon both targets and distractors suggests reduced ability to suppress responses to potential triggers for action. This may be related to increased sensorimotor noise or abnormal sensory gating.

An observational study of emotion regulation in children with Tourette syndrome

BACKGROUND

Explosive outbursts occur in 25%-70% of children with Tourette syndrome (TS) and may cause more distress than the tics themselves. Previous studies have indicated that a comorbid diagnosis of attention-deficit/hyperactivity disorder (ADHD) is associated with emotional dysregulation in TS; however, this relationship has almost exclusively been studied using parent-reported questionnaires.

METHODS

We examined emotion regulation (ER) with an observational measure in 150 medication-naïve children aged 7-12 allocated to four groups: Forty-nine children with TS, 23 children with ADHD, 16 children with TS + ADHD, and 62 typically developing controls. We assessed participants' ER ability, as well as parent-child interactions in the context of a complex puzzle task, and coded the observed behavior with the Tangram Emotion Coding Manual (TEC-M). We examined group differences in ER, as well as associations between ER and severity of symptoms pertaining to TS and ADHD.

RESULTS

Children with TS did not differ from controls in their ER ability. However, children with ADHD and TS + ADHD had more problems with ER than those with TS only and controls. Finally, parents of children with ADHD displayed more tension during the experimental task. ER ability was not associated with tic severity nor premonitory urges; however, better ER ability was associated with less severe symptoms of ADHD.

CONCLUSIONS

This study is the first to evaluate ER with an observational, clinician-rated measure in a controlled social setting in children with TS. Our findings support earlier questionnaire-based studies by showing impaired ER in children with TS + ADHD, but not in children with TS without comorbidity. These findings inform our understanding of the phenomenology of emotional dysregulation in TS and the role of comorbid disorders.

Aggression Toward Others Misdiagnosed as Primary Tics

Background

Tics describe a wide range of sudden and repetitive behaviors. Their multifaceted clinical features may resemble other explosive behaviors, including repetitive episodes of aggression toward others (allo-aggression) reported by subjects without tics. Here, we document 3 exemplary cases that help disentangle allo-aggressive behaviors from tics.

Cases

We report 3 cases who presented with an array of complex repetitive behaviors, most notably allo-aggression (eg, sudden kicking, hitting, slapping and biting others, or pushing someone off a bike), which were misdiagnosed as primary tics. In all cases, additional symptoms, such as blackouts, feeling of being controlled by different personalities, or being empowered by repetitive behaviors, and examination pointed toward different neuropsychiatric diagnoses.

Conclusions

Repetitive allo-aggressive behaviors are not part of the range of motor manifestations of tics. This observation not only has important medico-legal implications but is also relevant for the overall perception of Tourette syndrome and other primary tic disorders.

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.

Electrophysiology Echoes Brain Dynamics in Children and Adolescents With Tourette Syndrome-A Developmental Perspective

The development of the complex clinical picture of motor and vocal tics in children and adolescents with Tourette syndrome (TS) must be paralleled by changes in the underlying pathophysiology. Electrophysiological methods such as EEG and event-related potentials (ERPs) are non-invasive, safe and easy to apply and thus seem to provide an adequate means to investigate brain dynamics during this brain maturational period. Also, electrophysiology is characterized by a high time resolution and can reflect motor, sensory and cognitive aspects as well as sleep behavior. Hence, this narrative review focuses on how electrophysiology echoes brain dynamics during development of youngsters with TS and might be useful for the treatment of tics. A comprehensive picture of developmental brain dynamics could be revealed showing that electrophysiological parameters evolve concurrently with clinical characteristics of TS. Specifically, evidence for a maturational delay of motor inhibition related to cortico-spinal hyper-excitability and brain mechanisms for its cognitive compensation could be shown. Moreover, deviant sleep parameters and probably a stronger perception-action binding were reported. For neuromodulatory treatments (e.g., neurofeedback; repetitive transcranial magnetic stimulation, rTMS/transcranial direct current stimulation, tDCS) targeting neuronal deficits and/or strengthening compensatory brain mechanisms, pilot studies support the possibility of positive effects regarding tic reduction. Finally, attention-deficit/hyperactivity disorder (ADHD), as a highly frequent co-existing disorder with TS, has to be considered when using and interpreting electrophysiological measures in TS. In conclusion, application of electrophysiology seems to be promising regarding clinical and research aspects in youngsters with TS.