SYNCHRONIZATION BETWEEN MOTOR CORTEX AND SPINAL MOTONEURONAL POOL DURING THE PERFORMANCE OF A MAINTAINED MOTOR TASK IN MAN

1. Simultaneous recordings of cortical activity, recorded as the magne toencephalogram (MEG), and the electromyogram (EMG) of the ipsilateral and contralateral first dorsal interosseous muscles (1DI) were made d uring maintained voluntary contractions. 2. The MEG recorded from a lo calized region of the sensorimotor cortex of the dominant hemisphere w as coherent with the EMG from the contralateral 1DI muscle over a limi ted band of frequencies. The peak coherence was confined largely withi n the beta range of cortical activity (13-35 Hz). Significant cortical activity at 10 Hz and 40-50 Hz was not correlated with motor output. The MEG and EMG from the ipsilateral 1DI muscle were uncorrelated at a ll frequencies. 3. Significant coherence between the MEG and the EMG t vas associated with synchronous behaviour between the MEG and EMG in t he time domain, 4. The results demonstrate that synchronized cortical activity contributing to MEG activity within the beta range of frequen cies during maintained voluntary contractions is coupled to motor outp ut at frequencies of motor-unit activity associated with motor-unit sy nchronization. This observation provides further evidence for the invo lvement of cortical neurones in the generation of motor-unit synchroni zation. 5. We suggest that the coherence between MEG and contralateral EMG observed during maintained isometric contractions may provide an example of binding within the motor system.