A CORTICAL SLOW POTENTIAL IS LARGER BEFORE AN ISOLATED MOVEMENT OF A SINGLE FINGER THAN SIMULTANEOUS MOVEMENT OF 2 FINGERS

Movement-related cortical potentials (MRCPs) preceding voluntary, self -paced, simultaneous extension of the middle and index fingers (two fi nger movement) were compared with those preceding extension of the ind ex or middle finger alone (single finger movement) of the right hand i n 7 right-handed normal subjects. It was meant to double the number of muscles involved in the two finger movement as compared with the sing le finger movement and to activate only the motor cortex involving the movement of distal joints. The NS' (negative slope) amplitude with th e isolated middle finger movement was significantly larger at the prec entral area contralateral to the movement as compared with the two fin ger movement. The NS' amplitude with the index finger movement was als o larger than that with the two finger movement at the contralateral p recentral area. but the difference was not significant. It is postulat ed that greater activation of the primary hand sensorimotor area (HSMA ) contralateral to the movement might be necessary for the isolated mo vement of a single finger than for the two finger movement, although a smaller area of HSMA is expected to be activated in the former than i n the latter. The NS' may be related to central motor control processe s independent of muscle mass activated. As the single finger movement is considered to be more discrete and fine as compared with the simult aneous two finger movement, it is concluded that the HSMA plays an esp ecially important role in discrete and fine finger movement.