It has been a widely held view that Tourette’s — a condition that affects thousands and can seriously inhibit social interaction — is the result of the failure of control systems in the brain.
Though the repetitive vocal and physical tics characteristic of Tourette’s suggest an inability to control involuntary actions at the cognitive level, the latest findings contradict this and suggest the opposite may be the case. The Nottingham researchers have found evidence that young people with Tourette’s syndrome exhibit a greater level of cognitive control over their movements and speech than their unaffected peers do.
The constant need to suppress tics may have enhanced the brain processes that normally inhibit unwanted movement and speech, researchers believe.
The research findings offer new clues as to which regions of the brain may be involved in the generation of the syndrome’s characteristic behavioural tics. Georgina Jackson and colleagues report their findings in the March 21 issue of the journal Current Biology.
Tourette’s syndrome is a developmental disorder that typically occurs during late childhood and is characterised by the presence of chronic vocal and physical tics. Tics are involuntary, repetitive, highly stereotyped behaviours that occur with a limited duration, typically occur many times during a single day, and occur on most days.
Physical 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 (known as 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, Jackson and her 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 researchers, this finding most likely reflects a compensatory change in TS individuals — whereby chronic suppression of tics results in a generalised suppression of reflexive behaviour in favour of increased cognitive control.
“The findings are tremendously exciting and provide an important advance in our understanding of the behavioural consequences of Tourette’s syndrome,” says Jackson.
“Our current work is using ultra high-field brain imaging (MRI) techniques to understand the neural correlates of these behavioural changes. We would like to thank the Tourette’s patients and their families for their continued help with our research programme.”
Adapted from a Nottingham U press release.