Features of targeted arm movement after unilateral excisions that included the supplementary motor area in humans

The strategies used to make rapid targeted flexion movements at the elbow were assessed for the right and left arms of ten neurologically normal subjects and seven patients who had unilateral cortical resections that included all or part of one supplementary motor area (SMA). Visual targets were displaced either a constant distance (fixed step task) or a variable distance (variable step task). The reaction time (RT) for SMA patients as a group did not differ significantly from normal, although for some patients, RT exceeded the normal range bilaterally. Total movement time (TMT) was longer than normal for the SMA group, and again, increased TMTs tended to occur bilaterally. Both groups of subjects used a combination of duration and velocity scaling to adjust movement amplitude. In normal subjects, however, velocity scaling predominated, whereas in SMA patients, duration scaling was increased bilaterally. Our data indicate that the initiation of rapid elbow movement to a target presented visually is not consistently delayed after lesions that include part of the SMA, but the movement speed and strategy used to adjust movement amplitude may be changed bilaterally.