Enhanced negative slope of cortical potentials before sequential as compared with simultaneous extensions of two fingers.

Cortical potentials preceding voluntary sequential extension of the right middle finger followed by the index finger were compared with those preceding voluntary simultaneous extension of the two fingers in 7 right-handed subjects who were trained to make the total duration of the EMG discharges approximately the same between the two movements. The negative slope with the sequential movement started earlier and was larger, especially at the vertex and also at the bilateral precentral areas, as compared with the simultaneous movement. There was no difference in the Bereitschaftspotential amplitude between the two movements. It was postulated that a greater and earlier activation of the supplementary motor areas as well as the primary hand sensorimotor areas is associated, both bilaterally, with the execution of the unilateral sequential movement.