Inhibition, Disinhibition, and the Control of Action in Tourette Syndrome

Abstract

Tourette syndrome (TS) is a neurological disorder characterized by vocal and motor tics. TS is associated with impairments in behavioral inhibition, dysfunctional signaling of the inhibitory neurotransmitter GABA, and alterations in the balance of excitatory and inhibitory influences within brain networks implicated in motor learning and the selection of actions. We review evidence that increased control over motor outputs, including the suppression of tics, may develop during adolescence in TS and be accompanied by compensatory, neuromodulatory, alterations in brain structure and function. In particular, we argue that increased control over motor outputs in TS is brought about by local increases in 'tonic' inhibition that lead to a reduction in the 'gain' of motor excitability.

Investigating Habituation to Premonitory Urges in Behavior Therapy for Tic Disorders

“…Laboratory data suggest there is an inverse relation between tic severity and performance on a top-down cognitive-motor control task (Baym, Corbett, Wright, & Bunge, 2008), and that active tic suppression involves heightened activity in areas involved in top-down control (e.g., the left inferior frontal gyrus [Ganos et al, 2014]). A recent review found evidence suggesting that increased control over motor output, which could occur due to repeated tic suppression during development, leads to declining tic severity as affected individuals age (Jackson, Draper, Dyke, Pepes, & Jackson, 2015). Further, one recent investigation failed to find evidence for habituation across periods of reinforced tic suppression in children (Specht et al, 2013), but the researchers later reported that tics were less likely to occur following severe PMUs that were experienced during reinforced tic suppression periods than following less severe PMUs that were experienced during “free to tic” periods (Specht et al, 2014).…”

Neurocognitive predictors of treatment response to randomized treatment in adults with tic disorders

“…In fact, the majority of studies utilizing well-validated measures of executive function in TS/CTD samples indicated intact performance compared to controls (e.g., Eddy & Cavanna, 2014; Serrien et al, 2005; Thibault et al, 2009; Thomalla et al, 2014). Indeed, recent reviews of inhibitory control in TS conclude that there is no convincing evidence of deficits in inhibitory control (or executive functions) in TS/CTD (Jackson et al, 2015; Jung et al, 2013). In light of studies exhibiting enhanced motor inhibition in TS/CTD, it has been suggested that — This finding is consistent with the proposal that the frequent need to actively suppress tics leads to a generalised enhancement in the efficacy of volitional control mechanisms in TS that extends to laboratory tasks of cognitive control of motor output .” (Jung et al, 2013, p. 1017).…”

“…These include research utilizing Go/No-Go tasks (GNG; Serrien, Orth, Evans, Lees, & Brown, 2005; Thomalla et al, 2014; Watkins et al, 2005) and the Stroop task (Eddy & Cavanna, 2014; Thibault, O’Connor, Stip, & Lavoie, 2009). Very few studies found underperformance on tasks of behavioral inhibition in adults with TS/CTD (Jackson, Draper, Dyke, Pépés, & Jackson, 2015), but these results were found on tasks such as Sentence Completion, or the Simon task (Dursun, Burke, & Reveley, 2000; Georgiou, Bradshaw, Phillips, Bradshaw, & Chiu, 1995). In addition, it has been argued that such studies tend to include participants with comorbid disorders such as Attention Deficit/Hyperactivity Disorder (ADHD) and OCD, and that inhibitory deficits may be found mainly in individuals diagnosed with tic disorders concomitant with OCD and/or ADHD (Jung et al, 2013).…”

“…In addition, it has been argued that such studies tend to include participants with comorbid disorders such as Attention Deficit/Hyperactivity Disorder (ADHD) and OCD, and that inhibitory deficits may be found mainly in individuals diagnosed with tic disorders concomitant with OCD and/or ADHD (Jung et al, 2013). Notably, recent reviews of the literature highlight findings indicating a paradoxical superior behavioral control among adolescents and adults diagnosed with tic disorders compared to controls—hypothetically due to years of experience attempting to inhibit tics (Jackson et al, 2015; Jung et al, 2013). However, more research is required to support this notion, and the role of behavioral inhibition in adult TS/CTD remains unclear.…”

Deep Brain Stimulation for Tourette’s Syndrome: The Case for Targeting the Thalamic Centromedian–Parafascicular Complex

“…Many of the cortical regions modulated by CM-Pf DBS are structurally and functionally altered in TS (3). The effects of DBS on the activity of supplementary motor, premotor, and prefrontal cortex on the one hand and of the sensory network on the other are of special relevance due to the suggested role of these regions in tic generation and inhibition (32–35), and in PPI and sensorimotor gating, respectively (36). …”