FREQUENCY AND PHASE CHARACTERISTICS OF SLOW CORTICAL POTENTIALS PRECEDING BIMANUAL COORDINATION

The aim of the present study was to derive quantities which relate beh avioral and neurophysiological levels of observation during a bimanual coordination task. We recorded the scalp electroencephalographic (EEG ) signal preceding a sequence of 4 bimanual finger flexions of varying response rates in 12 subjects. A slow negative-going Bereitschaftspot ential (BP) displayed larger mean amplitudes and earlier onset times f or the faster required response rates. The amplitude of the BP was als o larger for electrode locations contralateral to the side initiating the behavioral response. A Fourier transform showed two predominant fr equencies (0.5 and 2.0 Hz) to be amplitude modulated as a function of the required response rate in addition to increased power on the contr alateral side of the finger initiating the response. A measure of the phase relationship between the left (C-3) and right (C-4) hemispheres of the fronto-central cortex at each of these spectral frequencies was calculated as well as the variance in this measure and found to corre spond closely to the variance in inter-response times derived from the subjects' movements. These findings indicate that changes in the stab ility and rate of a patterned movement are generally preceded by simil ar changes in the stability and amplitude of components observed on th e neurophysiological level.