[From movements to tics: neurophysiologic aspects]

The definition and classification of tics is still based on clinical data. Furthermore, in Gilles de la Tourette syndrome, organogenetic and psychogenetic determinants are still opposed and the true automatic involuntary nature of tics is still debated. Neurophysiological assessments can provide objective data, useful in analysing the physiopathology of tics. Simple tics consist of short bursts of EMG activity (lasting usually less than 100 ms) whereas complex tics consist of prolonged EMG activity. In both cases, the reciprocal activation of antagonist muscles may be present or absent. EEG recording has revealed abnormalities in about 25 to 75 p. 100 of Gilles de la Tourette patients but these findings lack specificity. Furthermore there is no EEG-EMG correlates with conventional techniques. However Obeso et al. have shown that simple tics are not prefaced by a normal premovement EEG potential, suggesting that simple tics are physiologically distinct from normal self-paced willed movements. Overnight polygraphic sleep studies show perturbation of the normal sleep pattern and stress the fact that tics may persist during all stages of sleep. Thus electrophysiological assessments give clues to the classification of tics as true abnormal automatic movements but also demonstrate their diversity. A biochemical cortico-subcortical dysfunction can be postulated.