Inhibitory deficits in tourette's syndrome

Abstract

A developmental approach to the study of psychopathology can broaden understanding of a wide variety of complex psychological disorders. This article reviews research on Tourette's syndrome (TS), a developmental disorder characterized by unwanted motor and vocal tics. Over the past decade, knowledge of the neurobiology and pathophysiology of TS has progressed rapidly. The application of brain imaging techniques, primarily magnetic resonance imaging, to the study of Tourette's has increased knowledge of structural and functional deficits in brain areas associated with behavioral and psychological disturbances in the disorder. By reviewing some of this work, we will describe one way in which knowledge of brain function in TS has both informed and been informed by a developmental science approach. In particular, we will consider the extent to which the cognitive and emotional development of persons with TS may be affected by specific neurobiological characteristics of the disorder.

Impaired inhibition of prepotent motor actions in patients with Tourette syndrome

“…The persistence of tic behaviour into adulthood may reveal deficient maturation of prefrontal-basal ganglia inhibitory control circuits in a vulnerable subset of patients. [33][34][35][36] In support of this idea, at least 1 study reported that reduced caudate nucleus volume in childhood was predictive of more severe tic symptoms in early adulthood. 37 Thus, participants with Tourette syndrome in our sample may be representative of this vulnerable subset of patients who continue to experience reduced inhibitory control over prepotent responses into adulthood.…”

“…12,13 Finally, stimulation of the subthalamic nucleus modulates inhibitory control in patients with Parkinson disease when performing the Simon task used in our study, 14 and imaging studies also suggest caudate nucleus involvement during conflict trials of the Simon task. 17,31 Given that patients with Tourette syndrome show morphometric and functional changes in these prefrontal and basal ganglia structures, 32,33 the circuits formed by these basal ganglia and prefrontal areas may be particularly important in understanding failures in inhibitory control over prepotent actions.…”

“…Interestingly, studies consistently report no differences in commission error rates between Tourette syndrome and control groups, a pattern that is similar to our finding that patients with Tourette syndrome do not show greater susceptibility to acting on strong prepotent, stimulus-driven response impulses. 33,[40][41][42][43] This further argues for differences between stimulus-driven action impulses and behavioural impulses associated with premonitory urges in patients with Tourette syndrome.…”

Stopping Manual and Vocal Actions in Tourette’s Syndrome

“…Alternatively, inhibitory control dysfunction in TS may be a key feature in subgroups of individuals who either show certain neuropsychiatric comorbidities or, as hypothesized by some in the literature, display an unremitting clinical course into adulthood. 10,11 One study showed that smaller caudate nucleus volumes in childhood predicted greater motor tic severity in adulthood, and several additional studies have reported abnormalities in prefrontal and basal ganglia circuitries among adults with persistent TS symptoms. 12,13 These patterns suggest that some patients with TS may experience specific alterations in frontal-basal ganglia structures that are also implicated in inhibitory control mechanisms.…”

“…Stopping, or inhibition, of initiated actions has been linked to the same prefrontal-basal ganglia circuitries putatively disrupted in adults with TS, thus providing a powerful test of the inhibitory control hypothesis of TS. 10,17 Notably, prior studies of inhibitory control in TS have focused exclusively on inhibition of manual responses. As a key novel component of our study, we investigated inhibitory control of both manual and vocal responses.…”