Sensorimotor mapping of volitional facial movements in Tourette Syndrome

BackgroundTourette Syndrome (TS) is a neurodevelopmental movement disorder involving involuntary motor and vocal tics believed to be characterised by disordered neural inhibition. Cortical representations have previously been manipulated by disruptions in the inhibitory neurotransmitter {gamma}-aminobutyric acid (GABA). However, while facial tics are the most reported motor tic, it is unclear if facial sensorimotor representations differ in TS. MethodsSixteen individuals with Tourette Syndrome (TS) or chronic tic disorder and twenty typically developing (TD) control participants underwent 3-Tesla functional magnetic resonance imaging (fMRI). Blood-oxygenation level-dependent (BOLD) responses were measured during a block-design task comprising cued facial movements of common facial tics (blinking, grimacing and jaw clenching). Activations in bilateral pre- and post-central cortices and supplementary motor areas (SMA) were examined. Conjunction analyses identified voxels commonly and uniquely activated across movements within each group. ResultsBoth groups showed significant activations in the bilateral sensorimotor cortices and SMA in response to blink, grimace and jaw clench movements, with no significant between-group differences. Between-group similarities were lowest for unique blink maps. Common voxel maps also revealed low between-group similarity, with reduced sensorimotor activation and no shared SMA activation across movements in the TS group. ConclusionVoluntary facial sensorimotor representations do not differ between groups. However, low similarities between group unique blink maps may reflect greater prevalence of blinking tics in TS. Additionally, reduced overlap in sensorimotor activation and absent common SMA engagement across cued movements in the TS group may indicate altered motor integration or action initiation.