The effects of external load on movement-related changes of the sensorimotor EEG rhythms.

The effects of external load opposing brisk voluntary extension of the right index finger on the EEG rhythms in the left and right sensorimotor hand area were studied in 13 right-handed subjects. Four levels of external loads corresponding to the weights of 0 g (no load), 30 g, 80 g and 130 g were used. The effects of external load on EEG rhythms were the following: (i) prior to movement, the desynchronisation of beta-rhythms (18-25 Hz) over the contralateral sensorimotor area was greater under the two largest loads as compared to the 0 g load. However, beta-desynchronisation at ipsilateral electrodes was larger under the 80 g load than under the 130 g load, presumably due to a transcallosally mediated inhibition exerted by the highly excited contralateral motor area; (ii) the mu-rhythm desynchronisation continued over both hemispheres for about 0.3-0.4 s after movement and the largest load was accompanied by the longest mu-rhythm desynchronisation; (iii) the post-movement beta-synchronisation was also longer under the heaviest load (130 g) as compared to the no-load condition (0 g), especially in subjects who prolonged their total movement time under the heaviest load. The results show that (i) the movement-related desynchronisation and synchronisation of sensorimotor EEG rhythms is influenced by external load opposing finger movement, and (ii) the effects of external load differ for the mu- and beta-rhythms.