Involuntary twitching, blinking, or grunting are common symptoms experienced by people with tics such as Tourette’s syndrome. Scientists have now discovered which regions of the brain are involved in the development of tics. Using case reports of people who developed tics after brain damage, scientists identified the relevant areas and compared their relationship to brain scans of more than 1,000 healthy people. They discovered a ‘network of tics’ and used Tourette patients to show that deep brain stimulation directed at this network could alleviate symptoms.
About one in a hundred children meets the diagnostic criteria for Tourette’s syndrome. The disorder usually manifests itself with motor and vocal tics, ranging from muscle twitching to involuntary use of bad language. In many, but not all, cases, symptoms improve with age. Other diseases can also lead to tics, including damage to the brain substance, for example from a stroke or accident. However, it is not yet fully understood exactly how tics develop.
In search of the source of the tics
A team led by Christos Ganos of Charité – Universitätsmedizin Berlin has identified a network of brain regions involved in tic development. “In recent years, neurological research has identified various areas of the brain that play a role in tics,” says Gano’s colleague Andreas Horn. “However, it remained unclear: which of these areas of the brain causes tics? Which of them are active instead to compensate for the flawed processes? We have now shown that it is not a single area of the brain that causes behavioral disturbances. Instead, tics are caused by a network of different brain areas malfunctioning.
To identify causal areas of the brain, researchers first analyzed 22 previously published case reports of patients who developed tics as a result of brain damage, such as after an accident or stroke. It was therefore clear in these people that the affected area of the brain must cause tics. Ganos and his colleagues have mapped in detail exactly where the damage is in the brain. They combined this data with over 1,000 brain scans of healthy people that showed how brain regions are connected to each other.
Brain region network as the culprit
Result: Mapped lesions are found in different areas of the brain – including the insular cortex, striatum, thalamus, and cerebellum – but these areas are connected by nerve connections and form a common network. “These structures perform a variety of functions, from motor control to emotional processing. They have all been discussed as possible tic triggers in the past, but so far no clear evidence has been found, and the direct link between these structures has also been unknown, ”says Gano’s colleague Bassam Al-Fatly. “We now know that these areas of the brain form a network and can cause tic disorders.”
While the findings are based only on data from people who acquired tics through brain damage – a relatively rare cause of tics – they appear to be extrapolated to Tourette patients. The researchers showed this in 30 people who had a pacemaker implanted for Tourette’s symptoms. This is to help in particularly severe cases where medications and behavioral therapy are not effective enough. Using brain scans, scientists determined exactly which regions of the brain were stimulated by the pacemaker. If these were parts of a newly identified tic network, the symptoms of those affected decreased the most.
“People with severe tic disorder benefit most when deep brain stimulation is directed at the tic network,” says Ganos. “In the future, we will incorporate this new discovery into the treatment of our patients, taking into account the tic network during brain pacemaker implantation. We hope that in this way we can even better alleviate the really high levels of suffering of those affected, to enable them to lead a largely self-determined and socially satisfying life. ‘
Source: Christos Ganos (Charité – Universitätsmedizin Berlin) et al., Brain, doi: 10.1093 / brain / awac009