Increased sensorimotor noise in Tourette syndrome

Tourette syndrome is a neurological disorder characterized by the occurrence of vocal and motor tics. The pathophysiology of Tourette syndrome has been linked to a substantial reduction in the number of inhibitory GABAergic interneurons found within the striatum, which may lead to increased neural 'noise' within the cortical-striatal-thalamic-cortical circuit implicated in movement production. In the current study, we used EEG to investigate increased neural noise in a group of 19 adults with Tourette syndrome compared to a matched neurotypical control group. We operationalized neural noise in this study as increased trial-by-trial variability in the magnitude and/or the timing of responses to a discrete somatosensory stimulation event. Specifically, we examined trial-by-trial variability in responses to a single pulse of median nerve electrical stimulation. Our results demonstrate that the P100 somatosensory evoked potential, which has been associated with conscious perception of tactile stimuli, was significantly increased in the Tourette syndrome group. Importantly, however, while the timing, temporal variability and spatial topography of early- and mid-latency somatosensory evoked potential components (e.g. N20, P45, N60, P100) did not differ in the Tourette syndrome group, when compared to matched controls, trial-by-trial variability was substantially increased in the Tourette syndrome group, but this was normalized in response to stimulation. These findings may indicate that the trial-by-trial recruitment of neuronal sensorimotor populations is less stable at rest in individuals with Tourette syndrome compared to controls but may normalize in response to stimulation.