Contrary to intuition, people who suffer from the motor and vocal tics characteristic of Tourette syndrome actually perform behavioral tests of cognitive motor control more accurately and quickly than their typically developing peers do. According to evidence reported online on March 24 in Current Biology, a Cell Press publication, that enhanced control arises from structural and functional changes in the brain that likely come about from the need to constantly suppress tics.
"The motor outputs of children with Tourette syndrome are under greater cognitive control," said Stephen Jackson of The University of Nottingham. "You might view this as their being less likely to respond without thinking, or as being less reflexive."
The researchers say that the findings may help to explain a long-standing puzzle in the field—why some individuals who have profound tics during childhood are relatively tic-free by early adulthood, whereas other individuals continue to have severe tics throughout their life. It also suggests that "brain training" approaches may help individuals gain control of symptoms associated with Tourettes and perhaps other neurological diseases, such as attention deficit hyperactivity disorder (ADHD) or obsessive-compulsive disorder (OCD), without the need for drugs or surgeries that may carry significant adverse effects.
An earlier study had shown that children with Tourette syndrome show enhanced cognitive control over their motor outputs and that the degree of their enhancement is inversely related to tic severity. Those findings offered the first indication that control over motor and vocal tics might be something that could be trained.
Based on that evidence, Jackson and colleagues wondered whether those enhanced cognitive control abilities might be accompanied by structural and/or functional alterations in the brains of individuals with Tourettes that might be seen by magnetic resonance imaging (MRI).
That suspicion has now been confirmed: the Tourettes brain shows alterations in the white-matter connections that allow different brain areas to communicate with one another, Jackson said. Brain scans also revealed changes in activity as indicated by blood flow when people with Tourette syndrome performed an executive function task.
The structural and functional changes observed were also strongly associated with clinical measurements of tic severity and executive function. In particular, the researchers found that changes in the frontal cortex of the Tourettes brain, the region most often linked to executive function, are strongly linked to levels of tic severity and executive task performance. They interpret this as evidence that the frontal cortex of the Tourette syndrome group reorganizes to help control the motor and vocal tics.
"Children growing up with a neurological disorder may develop adaptive changes in the way that their brain is organized that will help them overcome their difficulties and gain control over their symptoms," Jackson said.
There is one potential caveat: it may be that some people are simply born with the propensity to develop a particular profile of brain white-matter connections that allows them to gain control over their tics, whereas others with a different profile may not. To find out, the researchers are now planning a study in which they will follow people with Tourette syndrome and related neurodevelopmental disorders over time as their brains develop.
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