Tourette Syndrome: Complementary Insights from Measures of Cognitive Control, Eyeblink Rate, and Pupil Diameter

Abstract

Some individuals with Tourette syndrome (TS) have severe motoric and vocal tics that interfere with all aspects of their lives, while others have mild tics that pose few problems. We hypothesize that observed tic severity reflects a combination of factors, including the degree to which dopaminergic (DA) and/or noradrenergic (NE) neurotransmitter systems have been affected by the disorder, and the degree to which the child can exert cognitive control to suppress unwanted tics. To explore these hypotheses, we collected behavioral and eyetracking data from 26 patients with TS and 26 controls between ages 7 and 14, both at rest and while they performed a test of cognitive control. To our knowledge, this is the first study to use eyetracking measures in patients with TS. We measured spontaneous eyeblink rate as well as pupil diameter, which have been linked, respectively, to DA and NE levels in the central nervous system. Here, we report a number of key findings that held when we restricted analyses to unmedicated patients. First, patients’ accuracy on our test of cognitive control accounted for fully 50% of the variance in parentally reported tic severity. Second, patients exhibited elevated spontaneous eyeblink rates compared to controls, both during task performance and at rest, consistent with heightened DA transmission. Third, although neither task-evoked pupil dilation nor resting pupil diameter differed between TS patients and controls, pupil diameter was positively related to parentally reported anxiety levels in patients, suggesting heightened NE transmission in patients with comorbid anxiety. Thus, with the behavioral and eyetracking data gathered from a single task, we can gather objective data that are related both to tic severity and anxiety levels in pediatric patients with TS, and that likely reflect patients’ underlying neurochemical disturbances.

Tourette syndrome research highlights 2015

“…Two studies examined motor control. In a clever analysis of video recordings of the eyes 55 , spontaneous blink rate, which is related to dopamine levels, was higher in children with TS than in controls both during task performance and during a rest period. In contrast, pupil diameter, which is related to norepinephrine levels, was correlated with anxiety in TS subjects although not in controls.…”

The urge to blink in Tourette syndrome

“…Previous investigations have examined the resting blink rate in TS at rest or during various tasks. Some found an increased spontaneous blink rate in TS (Bonnet 1982; Tulen et al, 1999; Tharp et al, 2015), whereas another did not (Karson et al, 1985). Nevertheless, we show decreased suppression of the blink rate in TS during intentional suppression.…”

A Review of the Neuropsychological Dimensions of Tourette Syndrome

“…In Simon tasks, normal performance is often reported in both children [ 174 , 175 , 176 ] and adults [ 122 , 123 ]. However, impaired Simon task performance has also been found in children [ 177 ] and adults [ 178 ] with TS. In their study, Tharp et al [ 177 ] reported that tic severity was negatively correlated with accuracy and positively with response time (RT).…”

“…However, impaired Simon task performance has also been found in children [ 177 ] and adults [ 178 ] with TS. In their study, Tharp et al [ 177 ] reported that tic severity was negatively correlated with accuracy and positively with response time (RT). Such correlation between RT and tic severity was also reported in the study of Baym et al [ 175 ], suggesting that while TS patients’ performance in this type of task is usually intact [ 130 ], patients with severe tics could experience some difficulty.…”