SPATIAL EEG SYNCHRONIZATION OVER SENSORIMOTOR HAND AREAS IN BRISK ANDSLOW SELF-PACED INDEX FINGER MOVEMENTS

The changes of spatial EEG synchronisation during brisk and slow volun tary self-paced movements of the right and left index finger were anal ysed in 12 right-handed and 11 left-handed subjects. EEG was recorded from the left and right sensorimotor area using 24 closely spaced elec trodes. A novel measure of spatial EEG synchronisation, Omega-complexi ty, was computed separately for the left and right sensorimotor area i n 64 overlapping one-second epochs representing 4.5 s of the pre-movem ent and 3.5 s of the post-movement period. Omega-complexity was higher , hence spatial synchronisation was lower, in slow than in brisk movem ents, especially in the right-handed. A sustained increase of Omega-co mplexity was observed during execution of a slow movement. A decrease of Omega-complexity which was often associated with a brief burst of s patially synchronised 10-Hz oscillations occurred at the onset of exte nsor muscle contraction We suggest that increased spatial EEG synchron isation at movement onset may prevent ''spillover'' of excitation from the sensorimotor hand area to other cortical regions. During movement , the cortical neuronal assemblies subserve distinct, specialised func tions manifesting in increased Omega-complexity.