CONTRIBUTIONS OF THE MESIAL FRONTAL-CORTEX TO THE PREMOVEMENT POTENTIALS ASSOCIATED WITH INTERMITTENT HAND MOVEMENTS IN HUMANS

Two premovement potentials, the bereitschaftspotential (BP) and negati ve slope (NS'), can be recorded prior to the execution of self-paced h and movements using back-averaging of scalp electrical recordings. The contributions of the contralateral and ipsilateral primary motor cort ex (M1) and the mesial dorsal frontal cortex (MFC) to the generation o f the potentials were examined by simultaneously collecting positron e mission tomography (PET) scans and scalp recorded electrical activity for dipole source analysis in eight right-handed normal subjects. Subj ects performed simple unilateral thumb-finger opposition movements int ermittently with an average inter-movement interval of 7.4 s. PET was also collected for the same movement performed repetitively with inter -movement intervals of 0.5 s such that finger movements were nearly co ntinuous. PET studies of the intermittent movement revealed marked act ivation of the MFC in the region of the rostral supplementary motor ar ea (SMA) and cingulate motor area, contralateral sensorimotor cortex a nd no activation of the ipsilateral sensorimotor cortex. When the same movements were performed in a continuous repetitive manner, PET revea led strong contralateral sensorimotor and caudal MFC activation, and n o ipsilateral sensorimotor or rostral MFC activation. Dipole source so lutions of the back-averaged potentials for the intermittent movements were analyzed by testing dipole vectors placed into the regions of PE T activation. The premovement potentials were dominated by dipoles in the region of the MFC, with minimal contribution from either the contr alateral or ipsilateral MI. Activation in the region of the contralate ral M1 began near the onset of muscle activity. The orientation and ti ming of the MFC dipoles were consistent with both the BP and NS' poten tials originating from neurons in the rostral SMA and dorsal tier of t he cingulate sulcus and were appropriate for MFC activity to contribut e to both the preparation for movement and the descending activation o f spinal motor networks. (C) 1996 Wiley-Liss, Inc.