Movement preparation in Parkinson's disease. The use of advance information.

The effects of advance information on movement planning in parkinsonism were assessed by means of movement precuing. Using this technique, the response latencies of identical sets of movements were compared across conditions in which the degree and type of advance movement information were manipulated. Specifically, prior information concerning three movement dimensions (the direction and extent of forthcoming movements, as well as the limb to be used) was or was not provided. Eight patients with Parkinson's disease and 8 neurologically normal age-matched controls served as subjects. The experiment showed that the elevated reaction times of the Parkinsonian subjects are not primarily caused by delays in response selection. Estimates of specification times for each of the three dimensions showed only a modest slowing in parkinsonians. The specification of those movement dimensions unknown before the response signal appears to occur serially, and can occur in a variable order as in normals. Since parkinsonians can initiate movements with shorter latencies when partial or complete information is available, albeit more slowly than normals, we conclude that response selection and specification processes preceding rapid discrete movements are relatively unaffected by the disease. The overall slowness in movement initiation in parkinsonians as compared with normals may in part be caused by excessive delays in motor time and, in general, to those 'input' and/or 'output' processes which are unaffected by advance information.