The basal ganglia may be involved in bimanual co-ordination. Parkinson
's disease (which impairs basal ganglia output) is clinically reported
to cause difficulties in the performance of co-ordinated bimanual mov
ements. Nevertheless, any bimanual co-ordination difficulties may be t
ask specific, as experimental observations are equivocal. To infer the
role of the basal ganglia in co-ordinating the two arms, this study i
nvestigated the bimanual co-ordination of patients with Parkinson's di
sease. Sixteen Parkinson's disease patients and matched control subjec
ts performed a bimanual cranking task, at different speeds (1 and 2 Hz
) and phase relationships. All subjects performed the required bimanua
l in-phase movement on a pair of cranks, at fast (2 Hz) and slow (1 Hz
) speeds. However the Parkinson's disease patients were unable to perf
orm the asymmetrical anti-phase movement, in which rotation of the cra
nks differed by 180 degrees, at either speed; but instead reverted to
the in-phase symmetrical movement. For Parkinson's disease patients, p
erformance of the in-phase movement was more accurate and stable when
an external timing cue was used; however for anti-phase movement, the
external cue accentuated the tendency for patients to revert to more s
ymmetrical, in-phase movements.