People with Tourette’s syndrome can’t stop themselves from making sudden repeated movements or noises, so you might infer that they have an impairment in their mental control processes. On the contrary, according to a new study they actually have greater cognitive control than healthy people, suggesting the cause of their symptoms lies deeper, in their subcortical inhibitory mechanisms.
To test cognitive control, Sven Mueller and colleagues at the University of Nottingham asked nine young patients with Tourette’s and 19 controls to sometimes make fast eye movements towards an onscreen target, and sometimes to do the reverse – to make fast eye movements in the opposite direction to a target. A coloured border on the screen told them which rule to follow, and the rule changed every two trials. Switching between the two commands takes mental effort, especially when the natural reflex to look at a suddenly appearing target must be inhibited.
As expected, the participants were slower to respond whenever the rule changed, as they adjusted their mental ‘set’ to the new rule. However, to the researchers' surprise, without sacrificing their accuracy the Tourette’s patients actually slowed down less than the healthy controls.
The researchers said the patients’ superior performance at the task “may reflect a compensatory change in which the chronic suppression of tics results in a generalised suppression of reflexive behaviour in favour of increased cognitive control”.
“It is also consistent with the suggestion that the occurrence of vocal and motor tics does not result from a failure in inhibitory control at a cognitive level, but instead reflects a deficit in subcortical control mechanisms”, they added.
Mueller, S.C., Jackson, G.M., Dhalla, R., Datsopoulos, S. & Hollis, C.P. (2006). Enhanced cognitive control in young people with Tourette’s syndrome. Current Biology, 16, 570-573.
Tim Howard, a goal-keeper for Manchester United, has Tourette's and won humanitarian of the year in 2001 for his work with children with the condition.