Tourette syndrome is a developmental disorder characterized by involuntary, repetitive, and stereotyped movements or utterances. Now researchers reporting in the Cell Press journal Current Biology on September 25 have new evidence to explain how those with Tourette syndrome in childhood often manage to gain control over those tics. In individuals with the condition, a portion of the brain involved in planning and executing movements shows an unusual increase compared to the average brain in the production of a primary inhibitory neurotransmitter known as GABA.
The paradoxical findings—that the brains of people with Tourette syndrome produce more GABA than usual, not less—suggest that non-drug treatments that serve to increase the nerve messenger, such as brain stimulation, may speed the slow process whereby people with Tourettes naturally gain control over their disease symptoms. A major advantage of such an approach, the researchers say, is that, unlike the effect of drugs, such therapies might be targeted at the specific region where change is needed rather than the whole brain.
"In Tourette syndrome, as in many other disorders, the brain may adapt and reorganize the way it works so as to reduce or compensate for the effects of the disorder," says Stephen Jackson of the University of Nottingham. "In this case, the effects of excitatory signals that give rise to cortical hyperexcitability and unwanted movements may be compensated for by increased levels of GABA which act to 'damp-down' or reduce excitability within a localized brain area."
Jackson and his colleagues used a technique called magnetic resonance spectroscopy (MRS) to safely and noninvasively investigate levels of brain chemicals in individuals with Tourette syndrome. They were particularly interested in the amounts of GABA because of its status as the primary inhibitory neurotransmitter in the brain. They measured GABA in three brain regions—the primary motor cortex, the supplementary motor area (SMA), and a "control area" involved in visual processing—to find that people with Tourette syndrome had elevated concentrations of GABA only within the SMA.
The findings may have implications for the understanding and treatment of other neurodevelopmental conditions as well, Jackson notes, many of which are characterized by imbalances of excitatory and inhibitory influences in particular brain regions. Jackson says his team "will now explore whether this increased 'tonic' inhibition mechanism can be seen in other brain areas in Tourette syndrome, and also in other hyperactive disorders, such as obsessive compulsive disorder and autism, which are highly similar to Tourette syndrome and are often co-occurring."
Current Biology, Draper et al.: "Increased GABA contributes to enhanced control over motor excitability in Tourette syndrome."