The Direct Cortical Response: Associated Events in Pyramid and Muscle During Development of Movement and After-Discharge

Publisher Summary The changes in direct cortical response (DCR) components as they relate to the initiation of muscle contraction and cortical afterdischarge are presented in this chapter. Simultaneous examination of pyramid activity helps significantly in interpreting the changes observed in the cortical record. Medullary pyramid and muscle activity are studied in conjunction with the recording of the DCR in the monkey. In the cat, the suprasylvian cortex is probed with a recording electrode during afterdischarge. Similar observations are made upon the precentral motor cortex of the monkey. Upon the slow time line, a very weak stimulus evokes a 20 ms negative deflection known as the “primary potential,” which is followed by a lower amplitude and longer lasting positive known as the “after-positivity.” As the stimulus strength is increased, the primary potential grows in amplitude, while the after-positivity at first decreases and is then replaced by a slow, long-lasting, negative potential called the “slow negativity.” A single cortical stimulus is capable of evoking a muscle twitch, but the stimulus intensity required is considerably above that necessary to elicit a response in the medullary pyramid.