Most children with Tourette syndrome gain control over their tics gradually until they experience only mild symptoms by early adulthood. However, this is simply “too little, too late” since already their education and friendships have been spoiled by their condition. Now, a new study reveals how a chemical in the brain plays a vital role in controling the involuntary movements and vocal tics associated with Tourette syndrome.

Psychologists at the University of Nottingham found that higher levels of a neurochemical called GABA in a part of the brain known as the supplementary motor area helps to dampen down hyperactivity in the cortical areas that produce movement. "This result is significant because new brain stimulation techniques can be used to increase or decrease GABA in targeted areas of the cortex,” said Amelia Draper, a Ph.D. student and an author of the study.

The ABCs of Tourette Syndrome

Tourette syndrome (TS) is a developmental disorder characterized by involuntary and repetitive vocal and movement tics. Boys are about three to four times more likely than girls to develop the condition. Although the exact cause is unknown, research has shown that people with TS have unusual alterations in the wiring of brain regions involved in producing and controling motor functions. In particular, the primary motor cortex and the supplementary motor area are thought to be hyperactive in the brains of patients with this syndrome, causing the tics which can be both embarrassing and disruptive, especially for children. While tics can be partially controled, this often takes enormous mental energy and can leave patients exhausted by day’s end, plus, tics appear more frequently and excessively when a patient relaxes the self-control.

For the study, the scientists used a Magnetic Resonance Imaging scanner to measure the concentration of certain chemicals in the brain known as neurotransmitters. The chemicals were measured in the primary motor cortex and the supplementary motor area as well as an area involved in visual processing, the latter to be used as a site of comparison. The researchers tested a group of young people with Tourette syndrome and then compared them to tests from a group of typically developing young people with no known disorders.

They discovered those with Tourette had higher concentrations of GABA, which inhibits brain cell activity in the supplementary motor area. This came as a surprise because, as Professor Stephen Jackson explained, “prior to our finding, most scientists working on this topic would have thought that GABA levels in TS would be reduced and not increased as we show.” (Such an assumption would seem natural since GABA restrains activity and children with Tourette syndrome display too much activity, by way of their uncontrolable tics.)

Exploring further, the researchers used a technique called transcranial magnetic stimulation to provoke neuron activity and so reveal other aspects of brain function. Once again, the researchers felt surprise. When preparing to make a movement, those with the most GABA showed a dampening down of activity in the primary motor cortex, while the typically developing participants showed an increase in activity in that cortex. Finally, the researchers investigated the relationship of GABA to brain structure and saw how those with the highest levels of GABA also had the most connecting fibers in the corpus callosum, a structure connecting the two hemispheres of the brain. Having more connecting fibers, the researchers hypothesized, means more signals are being produced and this leads to the need for even more GABA to calm excess hyperactivity.

While more research must be done, these results could lead the way to more targeted approaches for controling tics. In particular, the researchers believe it may be possible to adjust the levels of GABA as a mechanism for helping young Tourette syndrome patients gain greater control over their tics.

Source: Draper A, Stephenson MC, Jackson GM, et al. Increased GABA Contributes to Enhanced Control over Motor Excitability in Tourette Syndrome. Current Biology. 2014.