Electrical signs of cortical involvement in the automatic control of grip force.

Evoked potentials were recorded in 10 subjects to assess cortical involvement in automatic control of grip force during restraint of a manipulandum held between finger and thumb. Brisk pulling loads elicited an increase in first dorsal interosseous EMG after 60.6 +/- 2.4 ms. Preceding this response were several time-locked scalp potentials, the most significant being a widespread negativity that appeared first over the frontal cortex and peaked 19.5 +/- 1.8 ms before the EMG peak, and a positivity that followed the EMG by 24.3 +/- 5.4 ms. The slope of the negativity and the amplitude of the positivity were greater than during passive conditions, suggesting that these potentials reflect cortical processes associated with automatic regulation.