Abstract
Tourette syndrome (TS) is a neurodevelopmental disorder characterized by the occurrence of motor and vocal tics. TS is associated with cortical-striatal-thalamic-cortical circuit dysfunction and hyper-excitability of cortical limbic and motor regions that lead to the occurrence of tics. Importantly, individuals with TS often report that their tics are preceded by premonitory sensory/urge phenomena (PU) that are described as uncomfortable bodily sensations that precede the execution of a tic and are experienced as an urge for motor discharge. While tics are most often referred to as involuntary movements, it has been argued by some that tics should be viewed as voluntary movements that are executed in response to the presence of PU. To investigate this issue further, we conducted a study using electroencephalography (EEG). We recorded movement-related EEG (mu- and beta-band oscillations) during (1) the immediate period leading up to the execution of voluntary movements by a group of individuals with TS and a group of matched healthy control participants, and (2) the immediate period leading up to the execution of a tic in a group of individuals with TS. We demonstrate that movement-related mu and beta oscillations are not reliably observed prior to tics in individuals with TS. We interpret this effect as reflecting the greater involvement of a network of brain areas, including the insular and cingulate cortices, the basal ganglia and the cerebellum, in the generation of tics in TS. We also show that beta-band desynchronization does occur when individuals with TS initiate voluntary movements, but, in contrast to healthy controls, desynchronization of mu-band oscillations is not observed during the execution of voluntary movements for individuals with TS. We interpret this finding as reflecting a dysfunction of physiological inhibition in TS, thereby contributing to an impaired ability to suppress neuronal populations that may compete with movement preparation processes.
Highlights
Tourette syndrome (TS) is a neurological disorder of childhood onset that is characterized by the presence of chronic vocal and motor tics (Cohen, Leckman, & Bloch, 2013)
It is of interest to note that Parkinson’s disease – a disorder that is associated with a poverty of spontaneous movements (Akinesia), slowed movements (Bradykinesia), and is caused by a loss of dopamine cells within the substantia nigra – is associated with abnormally increased power in beta-band oscillations, that is reduced by dopamine medication and deep-brain stimulation
Tourette syndrome – a disorder that is associated with the occurrence of involuntary movements and vocalizations, and is associated with increased dopamine activity within the cortical–striatal–thalamic–cortical motor circuit (Buse et al, 2013) – is shown in the current study to be associated with an absence of betaand mu-band desynchronization ahead of the occurrence of motor tics
Summary
Tourette syndrome (TS) is a neurological disorder of childhood onset that is characterized by the presence of chronic vocal and motor tics (Cohen, Leckman, & Bloch, 2013). It has been suggested that these movement-related brain oscillations, the beta-band oscillations, reflect an internal estimate of the likelihood of the need for a novel voluntary action, and in effect signal motor readiness (Jenkinson & Brown, 2011). If this is the case one might make the following predictions. If tics are essentially involuntary movements, we would expect to see clear evidence for movement-related ERD when individuals with TS execute volitional movements, but not necessarily when they execute motor tics. The current study investigated this issue using EEG-recording techniques
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