EEG rhythms of the sensorimotor region during hand movements.

The aim of this study was to determine what motor behaviors or conditions were associated with an increased occurrence of beta activity in the sensorimotor region of human subjects. EEG recordings were obtained from 8 electrodes symmetrically arranged around C3, with 3 cm interelectrode spacing. The electrode montage allowed calculation of the Laplacian operator at two positions, C3r and C3c, overlying the hand area of the motor cortex and of the somatosensory cortex, respectively. A variety of tasks involving right-hand movements of different levels of complexity, attention and preparation were performed. The corresponding EEG power spectra were subsequently computed for frequencies between 7 and 50 Hz. Repetitive hand movements alone (either drawing circles or writing one's signature) did not result in significantly increased beta activity in the sensorimotor region compared to relaxed conditions. However, both motor preparations and focused attention, whether movements were performed or not, were associated with an increase of high frequency beta activity (30-50 Hz) in the sensorimotor region. Therefore, the facilitatory effect of attention and motor preparation and not the functional activation of the sensorimotor cortex by hand movements was associated with an increase in synchronized fast beta activity.