Force uncertainty of voluntary movement and human movement-related potentials.

Five movement related potentials, the Bereitschaftspotential (BP), the pre-motion positivity (PMP), the motor potential (MP), the first negative potential during the movement (N1) and the late positive component (LPC) were recorded from human subjects performing right index finger flexions under conditions when the resistive forces (70 N/cm or 10 N/cm) were predictable and when they were unpredictable. The BP was larger prior to the larger force in the certain condition. In the uncertain condition, the BP was similar to that associated with the larger force in the certain condition suggesting that the subjects tended to prepare for the heavy resistance when confronted with force uncertainty. The MP revealed enhanced negativity over the left parietal cortex when the force was unpredictable. The N1 was significantly larger during the high force movement, especially in the uncertain condition. The results support the view that pre-movement compensation for force unpredictability does exist as reflected by the MP over the parietal areas.