FACILITATION OF MOTOR EVOKED-POTENTIALS (MEPS) IN FIRST DORSAL INTEROSSEOUS (FDI) MUSCLE IS DEPENDENT ON DIFFERENT MOTOR IMAGES

Objective: We investigated changes in motor evoked potentials (MEPs) t o explain why mental practice can improve motor performance. Methods: MEPs were recorded from right and left first dorsal interosseous (FDI) muscles of 9 normal, right-handed subjects during different motor ima ges of index finger movement: (1) rest, (2) flexion, (3) abduction, (4 ) extension. A paired t test was used to compare differences of stimul us intensities and MEP amplitudes among conditions. Results: MEP ampli tudes significantly increased in both FDI muscles during motor images of flexion and abduction but not of extension. Moreover, MEP amplitude s were larger in flexion than in abduction. These differences were pro portional to the amount of real EMG discharge of FDI muscle in the sel ected direction of index finger movement. With regard to right-left di fferences, MEP amplitudes in the right FDI muscle were larger than tho se in the left. Conclusions: The primary motor cortex plays a role in the mental representation of motor acts. Furthermore, the amount of co rticomotoneuronal cell activity is affected by the different motor ima ges utilizing the same muscle. Right-left difference of MEP amplitude supports the view of left-hemisphere dominance for motor programming a s an aspect of normal brain function among right-handers. (C) 1998 Els evier Science Ireland Ltd. All rights reserved.