Though the repetitive vocal and motor tics characteristic of Tourette's syndrome may suggest an inability to control involuntary actions at the cognitive level, researchers have now found evidence that young people with Tourette's syndrome actually exhibit a greater level of cognitive control over their movements than their non-affected peers do. The research findings are consistent with a greater need for cognitive control of actions in individuals with Tourette's syndrome, and they offer clues to which regions of the brain may be involved in the generation of the syndrome's characteristic behavioral tics.
Tourette's syndrome is a developmental disorder that typically occurs during late childhood and is characterized by the presence of chronic vocal and motor tics. Tics are involuntary, repetitive, highly stereotyped behaviors that occur with a limited duration, typically occur many times during a single day, and occur on most days. Motor tics can be simple or complex in appearance, ranging from simple repetitive movements to coordinated action sequences. Verbal tics may involve repeating words or utterances (palilalia), producing inappropriate or obscene utterances (coprolalia), or the repetition of another's words (echolalia). Understanding the psychological processes and neural mechanisms that give rise to the execution of tics is of considerable clinical importance. A widely held view is that the inability to suppress unwanted movements in Tourette's syndrome results from a failure of cognitive control mechanisms.
In the new work, Dr. Jackson and colleagues studied cognitive control mechanisms in a group of young people with Tourette's syndrome (TS) by assessing the performance of individuals on a goal-oriented eye-movement task. The task demanded high levels of voluntary control and the active inhibition of automatic eye movements. The researchers found that in performing the task, TS individuals are not in fact impaired in cognitive control. Instead, the study showed that, paradoxically, TS individuals make fewer error responses than their age-matched and neurologically normal peers do, while responding just as fast to the task's demands. According to the authors, this finding most likely reflects a compensatory change in TS individuals whereby the chronic suppression of tics results in a generalized suppression of reflexive behavior in favor of increased cognitive control.
The researchers include Sven C. Mueller, Georgina M. Jackson, Ranu Dhalla, Sophia Datsopoulos, and Chris P. Hollis of The University of Nottingham in Nottingham, United Kingdom. This work was funded by BBSRC grant S18280 to G.M.J.
Mueller et al.: "Enhanced Cognitive Control in Young People with Tourette's Syndrome." Publishing in Current Biology 16, 570-573, March 21, 2006. DOI 10.1016/j.cub.2006.01.064
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