Tackling Tics: Understanding the Brain-Basis of Tic Disorders
By Lisa Keenan
Tics are involuntary, unwanted sounds and movements of the body. This means that a person might make the same sound or movement over and over again, and not be able to stop. These sounds are called vocal tics and the movements are called motor tics. Some people might be able to suppress or ‘hold in’ their tics for a short period of time, but eventually they have to let them out.
Tics are more common than you might think! Around 1 in 5 children will experience tics at some point during childhood,1 and 1 in 100 will have tics that persist, often into adulthood.2 This means that there are lots of people with tics, even if you never realised or noticed!
Tics that stick
When tics stick around for more than a year, doctors might call it a persistent tic disorder. There are three recognised types of persistent tic disorders. Persistent motor tic disorder is characterised by motor tics; Persistent vocal tic disorder is characterised by vocal tics; and Tourette syndrome is characterised by both motor and vocal tics. It is not fully understood why some people continue to have tics and others only experience them for a short time. Persistent tic disorders are known to run in families, but the exact causes and genetics involved are still being explored. 3
What do tics look like?
There are hundreds, if not thousands, of different types of tics. There are some that are very common and simple, like excessive blinking, eye rolling, sniffling, or throat clearing. But tics can be almost anything. Just think of any random movement or noise you can make. Do you have something in mind? Whatever you thought of, it can probably be a tic! While they are less common, some tics can be highly complex movements and sounds, like jumping, spinning, or repeating words and phrases. Other tics might go completely unnoticed to onlookers, like tensing stomach muscles or making barely audible sounds. Can you think of any others?
Tics wax and wane, meaning that some days they can be quite intense and frequent, while other days they might not show up much at all! The types of tics someone experiences can also change – sometimes even on a daily basis.
What do tics feel like?
If you’ve never experienced tics before, it might be difficult to imagine what it might feel like. While the experience is different for everyone, some people with tics have come up with analogies to help others understand what it’s like. For example, try to not blink for as long as you can. After a while, your eyes will probably start to feel quite uncomfortable! In tic-lingo, this sensation is known as a premonitory urge.4 Eventually, you may either decide that enough is enough and give in or your eyes will involuntarily blink (maybe even without you realising). Tics have also been compared to an uncomfortable itch, and that resisting the urge to tic is like resisting the urge to scratch a very strong itch.
Can you think of any other examples?
What parts of the brain cause tics?
If you have been keeping up with our blog so far, it may come as no surprise that there is no simple explanation, and that there are in fact lots of different brain areas involved in tics! Scientists are still working to develop a clear and comprehensive model to explain the brain-basis of tics. Some of the earliest research has centred around the basal ganglia – a collection of structures located at the base of the brain that regulate movement. A number of studies have found that, on average, children and adults with Tourette syndrome have smaller basal ganglia than the general population.5
Image credit: Beckie Port, licenced under CC BY-SA 3.0
There also seems to be an issue with something called the cortico–striato–thalamo–cortical network,6 which causes hyperexcitability in the motor cortex. In other words, the part of the brain in charge of movement seems to be a bit too active! You can read more about how the motor cortex produces movements in a previous blog post here.
Interestingly, brain scanning studies have revealed that the supplementary motor area appears to behave differently depending on whether movements are intentional or due to tics.7 This means that even if two people are making the exact same movement (one intentionally and one due to tics), the brain knows the difference! This is important to realise, because even though some tics might look like purposeful behaviours, they are not.
The complexity of persistent tic disorders
There is no simple, clear-cut explanation for why tics occur and how the brain causes them. Persistent tic disorders are complex conditions, so it makes sense that there is likely a complex explanation! While tics are the most visible symptom, a number of co-occurring conditions and symptoms are common in children and adults with persistent tic disorders. These include attention-deficit hyperactivity disorder (ADHD), obsessive-compulsive disorder (OCD), autism spectrum disorder (ASD), sensory processing issues, executive dysfunction, and sleep difficulties.8 No two individuals are affected in exactly the same way, and may experience a different combination of symptoms. But for most people, tics are just the tip of the iceberg!
- Black, K. J., Black, E. R., Greene, D. J., & Schlaggar, B. L. (2016). Provisional tic disorder: What to tell parents when their child first starts ticcing. F1000research, 5, 696. https://doi.org/10.12688/f1000research.8428.1
- Scharf, J. M., Miller, L. L., Gauvin, C. A., Alabiso, J., Mathews, C. A., & Ben‐Shlomo, Y. (2015). Population prevalence of Tourette syndrome: A systematic review and meta‐analysis. Movement Disorders, 30(2), 221–228. https://doi.org/10.1002/mds.26089
- Pauls, D. L., Fernandez, T. V., Mathews, C. A., State, M. W., & Scharf, J. M. (2014). The inheritance of Tourette disorder: A review. Journal of Obsessive-Compulsive and Related Disorders, 3(4), 380–385. https://doi.org/10.1016/j.jocrd.2014.06.003
- Takon, I., Rickards, H., Chowdhury, U., & Sharma, S. (2015). I get this feeling like grapes bubbling through and I try hard to press them in: A qualitative study of premonitory urges in children with tic disorders. Journal of Neurology, Neurosurgery & Psychiatry, 86(9), e3-e3. https://doi.org/10.1136/jnnp-2015-311750.38
- Felling, R. J., & Singer, H. S. (2011). Neurobiology of Tourette syndrome: Current status and need for further investigation. Journal of Neuroscience, 31(35), 12387–12395. https://doi.org/10.1523/JNEUROSCI.0150-11.2011
- Debes, N., Jeppesen, S., Raghava, J. M., Groth, C., Rostrup, E., & Skov, L. (2015). Longitudinal magnetic resonance imaging (MRI) analysis of the developmental changes of Tourette syndrome reveal reduced diffusion in the cortico-striato-thalamo-cortical pathways. Journal of Child Neurology, 30(10), 1315–1326. https://doi.org/10.1177/0883073814560629
- Hampson, M., Tokoglu, F., King, R. A., Constable, R. T., & Leckman, J. F. (2009). Brain areas co-activating with motor cortex during chronic motor tics and intentional movements. Biological Psychiatry, 65(7), 594–599. https://doi.org/10.1016/j.biopsych.2008.11.012
- Groth, C., Debes, N. M., Rask, C. U., Lange, T., & Skov, L. (2017). Course of Tourette syndrome and comorbidities in a large prospective clinical study. European Journal of Paediatric Neurology, 21, e22-e22. https://doi.org/10.1016/j.ejpn.2017.04.1139
Further resources
Video link: ‘How do you live with Tourette’s?’
Video link: ‘The Neuroscience of Tourette Syndrome’
Links to support organisations: Tourettes Action, Tourette Association of America, Tourette Canada
