Impairment of movement initiation and execution but not preparation in idiopathic dystonia

Imaging studies have reported impaired activation of the striatum and their frontal projection sites in dsytonia, areas which are considered to play a role in motor preparation, movement initiation and execution. The aim of t his study was to investigate the processes of motor preparation, response i nitiation and execution in patients with idiopathic torsion dystonia (ITD). We assessed 12 patients with ITD and 12 age-matched controls on a number o f reaction time (RT) tasks that differed in degree of motor preparation pos sible. Subjects performed a visual simple RT (SRT) task, an uncued four-cho ice reaction time (CRT) task and a fully precued four-choice RT task. A sti mulus 1-stimulus 2 (S1-S2) paradigm was used. The warning signal/precue (Sl ) preceded the imperative stimulus (S2) by either 0 ms (no warning signal o r precue) 200 ms, 800 ms, 1,600 ms or 3,200 ms. The patients with ITD had s ignificantly slower RTs and movement times than normals across all RT tasks . The unwarned SRT trials were significantly faster than the uncued CRT tri als for both groups. For both groups, precued CRTs were significantly faste r than the uncued CRTs. The results show that while response initiation and execution are significantly C, slower in patients with ITD than normals, m ovement preparation is not quantitatively or qualitatively different. The r esults are discussed in relation to previous imaging, behavioural and elect rophysiological studies and models of fronto-striatal dysfunction in ITD.