Brain chemical could be key to controlling Tourette syndrome tics

Researchers have identified a chemical in the brain as one that could play a major role in controlling the involuntary movements and vocal outbursts associated with Tourette syndrome.

Experts believe that the development of Tourette syndrome is linked to damage or abnormality in the basal ganglia of the brain.

By identifying the importance of this neurochemical, the research team from the University of Nottingham, UK, may have established a target for the development of new forms of treatment.

The researchers found that higher levels of the neurochemical GABA in an area of the brain called the supplementary motor area (SMA) helped to reduce hyperactivity in the cortical areas of the brain responsible for movement.

People with Tourette syndrome have too many signals being sent to these cortical areas, leading to unwanted and occasionally inappropriate movements or sounds known as tics that the person may have little or no control over.

By reducing the hyperactivity in areas such as the SMA and the primary motor cortex (M1), only the strongest signals can be processed and 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. It may be possible that such techniques to adjust the levels of GABA in the SMA could help young people with [Tourette syndrome] gain greater control over their tics.

Many people with Tourette syndrome can partially control their tics, but this is an exhausting process that can lead to tics becoming more frequent when they are tired at the end of the day. In young people in particular, Tourette syndrome can have a very disruptive influence on education and social friendships.

Increased levels of GABA

For the study, the researchers measured the levels of neurotransmitters in the brain with a technique called magnetic resonance spectroscopy (MRS) inside an MRI scanner. In particular, they measured neurotransmitters in the SMA, the M1 and an area used in visual processing (V1) as a site of comparison.

Fast facts about Tourette syndrome

• In the US, 1-2% of the population are believed to have Tourette syndrome
• Simple tics are often sudden and repetitive, including jerking, blinking, coughing and yelling.
• Complex tics include making obscene gestures (copropraxia) and repeating what other people say (echolalia).

The researchers examined a group of young people known to have Tourette syndrome and compared them with an age- and gender-matched group of people with no known disorders. 

Interestingly, the participants with Tourette syndrome were found to have higher concentrations of GABA in the SMA.

The team then explored the result in greater detail. Using a functional MRI, the researchers observed that having more GABA in the SMA meant that people with Tourette syndrome had less neurological activity within the SMA when performing a simple motor task such as tapping their finger.

Next, the researchers used a magnetic field to stimulate neuron activity in the brain, in a process called transcranial magnetic stimulation (TMS). 

They found that the people with the most GABA inhibit neuron activity in the M1 when preparing to make a movement. In contrast, people from the control group were found to increase their activity.

The researchers also found that within the corpus callosum - the white matter fiber bundles that connect the two sides of the brain - people with the highest levels of GABA also had the most connecting fibers.

This finding prompted the conclusion that the more connecting fibers there are, the more excitatory signals are being produced. There is then a greater need for GABA in order to calm down this hyperactivity.

A 'paradoxical' finding

The research team was surprised by the result. This finding is paradoxical because prior to our finding, most scientists working on this topic would have thought that GABA levels in [Tourette syndrome] would be reduced and not increased as we show.

"This is because a distinction should be made between brain changes that are causes of the disorder (e.g., reduced GABA cells in some key brain areas) and secondary consequences of the disorder (e.g., increased release of GABA in key brain areas) that act to reduce the effects of the disorder."

Their findings, published in Current Biology, could lead to more targeted approaches to controlling disruptive tics. A form of neurostimulation called transcranial direct-current stimulation (tcds) has already been found to be successful in altering the levels of GABA in targeted cortical areas.

The researchers also said that the next steps for the team will be to observe whether these results are found elsewhere in the brains of individuals with Tourette syndrome.

They are also keen to investigate further the role that alterations to the balance of excitatory and inhibitory influences in the brain play in other conditions, such as obsessive-compulsive disorder (OCD), attention deficit hyperactivity disorder (ADHD) and autism.

If these findings can be expanded upon, this research could be extremely beneficial in changing the ways in which common neurodevelopment disorders - such as Tourette syndrome - are treated.

At the start of the year, researchers reported on a study that confirmed a rare genetic mutation as a cause of Tourette syndrome.