Self-initiated and externally-triggered sequential arm movements in dystonia

We studied the execution of self-initiated (SI) and externally-triggered (ET) rapid sequential arm movements in normal subjects (n = 7) and patients with generalised dystonia (n = 8) involving the upper limbs. We obtained 3Dkinematic measurements by the ELITE- system (BTS). Reaction time (RT) and movement time (MT) for each submovement of the sequences were recorded and statistically analysed (ANOVA, p<0.01). Subjects performed S-step zig-zag sequences signalled by 6 visual targets (empty squares) on a screen. In the ET-condition subjects moved in response to the consecutive filling of each squared target. In the Si-condition subjects moved on their own decision along previously filled targets. We also analyzed RT and MT for a single movement identical to the first submovement of the sequence. Compared with controls, during the ET-condition patients showed similar RT for single and slower RT for sequential movements. RT did not change-with sequence progression in neither group. Patients also show longer MTs than controls during both kind of movements and conditions. Patients executed SI- and ET-sequences at similar speed, whereas controls moved significantly faster during SI- than ET-condition. These results suggest that bradykinesia in generalised dystonic patients do not rely on the modality of movement execution.