Can the brain tell how sensitive we are?

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Many individuals with TS describe experiencing uncomfortable bodily and cognitive sensations that come before their tics

As well as hearing from people affected by Tourettes Syndrome we wanted to hear from the voices of people involved in research. In our recent blog Jacob Ogden described his experience of being involved as a research participant. In this blog we hear from the PhD research student involved in that project, Hilmar, who tells us about the background for this research at the School of Psychology, University of Nottingham.

Can the brain tell how sensitive we are?

As we grow from infancy to adulthood, our different sensory systems develop. Most commonly we hear about the five senses: visual (sight), auditory (hearing), olfactory (smell), gustatory (taste), and touch (somatosensory) systems. However, we can add to those categories: our sense of balance (vestibular sensory system) and the sensory system responsible for the sense of our body in space (called proprioception). Our brain combines and makes sense of information coming from both our body and our environment. In addition, sensory information can trigger our actions, for example bright light triggers us to close our eyes. But how is this relevant to Tourettes syndrome?
In addition to having unwanted motor movements and vocalizations, many individuals with TS describe experiencing uncomfortable bodily and cognitive sensations that come before their tics. These sensations have collectively been labelled premonitory sensory phenomena (or premonitory urges, sometimes known as a tic signal). Some people believe that tics occur to remove these uncomfortable bodily sensations. One of the first descriptions of these sensations was written by Joseph Bliss, who himself had a diagnosis of TS. In his article he wrote: “All of the Tourette syndrome (TS) actions are extravagant extensions of more or less ordinary bodily actions... What is basic to TS overt actions is the intolerable need to…gratify and terminate an almost intolerable urge” (Bliss, 1980). Here Bliss is describing tics as being the extreme version of normal everyday actions. Consequently, many people with TS feel the need to suppress their tics in social situations, leading to an uncontrollable urge to tic. Bliss also describes experiencing increased intensity of sensation from both internal and external sources. Some motor and vocal tics may be driven by sensory events (Eapen, Morarty, and Robertson, 1994).  Reflex tics may occur in a response to an external stimulus (for example coughing in the presence of someone with TS). Sensory tics may occur in response to stimuli arising from outside the body (for example a tingling or itching sensation) or from an internal bodily sensation (for example when you cough).
Previous research has shown that the majority of patients say that they are especially sensitive to sensory information (Cohen and Leckman, 1992; Belluscio, et al. 2011). Most common complains include irritation caused by certain sounds or clothing tags scraping against their skin causing uncomfortable sensations. These sensations can also lead to the production of tics in patients (Commander, et al. 1991; Eapen Morarty and Roberson, 1994). Surprisingly, in the research setting researchers have been unable to show that patients with TS are more sensitive to sensory information than individuals without TS. So why do people with TS think that they are super sensitive?
A team of researchers at the University of Nottingham, lead by Professors Stephen R. Jackson and Georgina M. Jackson, are now conducting a new and interesting research study. This study involves using Transcranial Magnetic Stimulation (TMS for short) to assess the responsiveness of muscles in the body by stimulating parts of the brain called the motor cortex. Neurons in our brain communicate with each other in a specific way using chemical messengers called neurotransmitters. Previous research has shown that patients with TS demonstrate a significant decrease of specific messengers responsible for relaying messages from one neuron to the next (Kalanithi et al. 2005; Kataoka, et al. 2010). With TMS we can assess this communication and study connections between the brain and muscles in our body. Moreover, by measuring the response from the muscles after stimulating the brain we can assess the location and size of these muscle representations, the distance between different muscle representations (for example distance between hand and shoulder muscles), and compare this between individuals with and without TS.
The researchers are currently recruiting patients with TS aged 13 and older. If you and your child might be interested, please get in touch with Jane Fowlie, research nurse (Tel: 0115 9515316) or the researcher Hilmar Sigurdsson.

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