Abstract

Gilles de la Tourette's syndrome (TS) is a neuropsychiatric movement disorder characterised by the presence of multiple tics. Tics have an unusual, intermediate status between voluntary and involuntary movements. This ambiguity might involve not just a disorder of movement generation but also an abnormality of voluntary experience. Here the experience of voluntary movements in adult patients with TS is investigated and compared with healthy controls. A group of adult TS patients and age matched control participants estimated the time of conscious intention to perform a simple keypress movement and movement onset. Patients with TS showed a delayed experience of intention relative to controls whereas estimates of the actual movement onset were similar for patients and controls. These data suggest an abnormal experience of volition in patients with TS. Delayed volition could either be an additional intrinsic feature of the syndrome or it could reflect a cognitive strategy to limit motor excitability, and thus tic generation, during voluntary action.