Parkinson's disease patients showed delayed awareness of motor intention.

Although dopamine plays an important role for motor control and modulates the frontal function via basal ganglia-thalamo-cortical loop, it is not known whether dopamine can affect the awareness of motor intention or not. To test this hypothesis, we applied Libet's clock paradigm to Parkinson's disease (PD) patients. Thirteen PD patients and 13 age-matched, healthy controls took part in the experiment which consisted of three judgment paradigms: W, M and S judgment. In W and M judgments, subjects were asked to press the key at self-willed timing. In W judgment, subjects reported the location of the clock's hand when they became aware of the intention (W-time). In M judgment, subjects reported the time when they became aware of the actual movement (M-time). In S judgment, subjects reported the time of the electrical stimulation given to their hand (S-time). W-time was significantly shorter in PD patients than in healthy control subjects while M-time and S-time were not different between the two groups. Delayed awareness of motor intention but not of action in PD patients might be related to dopamine depletion in those patients.