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 sensorimo tor 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, 8 0 g and 130 g were used. The effects of external load on EEG rhythms w ere the following: (i) prior to movement, the desynchronisation of bet a-rhythms (18-25 Hz) over the contralateral sensorimotor area was grea ter 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 transcallosal ly mediated inhibition exerted by the highly excited contralateral mot or area; (ii) the mu-rhythm desynchronisation continued over both hemi spheres for about 0.3-0.4 s after movement and the largest load was ac companied by the longest mu-rhythm desynchronisation; (iii) the post-m ovement beta-synchronisation was also longer under the heaviest load ( 130 g) as compared to the no-load condition (0 g), especially in subje cts who prolonged their total movement time under the heaviest load. T he results show that (i) the movement-related desynchronisation and sy nchronisation of sensorimotor EEG rhythms is influenced by external lo ad opposing finger movement, and (ii) the effects of external load dif fer for the mu- and beta-rhythms. (C) 1997 Elsevier Science Ireland Lt d.