Load effect on background rhythms during motor execution: A magnetoencephalographic study

We investigated the effect of load against self-paced movement on cortical involvement for motor execution. Ten right-handed healthy volunteers were requested to perform brisk extension of the right index finger at self-paced intervals exceeding 10 s for three load conditions: 0 g, 50 g and 100 g. Movement-related magnetic fields were recorded using an MEG system. The signals were band-pass-filtered through 18-23 Hz and rectified before averaging with respect to EMG onset. We analyzed the time course and %change of peak amplitude with reference to the baseline amplitude in event-related desynchronization (ERD) or synchronization (ERS) in each hemisphere. Maximum response was observed around the left somatomotor area for all conditions. ERD did not show any significant difference before the movement onset among the three load conditions. For %change, ERS in the post-movement period was significantly larger for the 100 g load condition than for the 0 g load condition, and that was significantly greater over the left than over the right hemisphere. These findings indicate that the load has little effect on pre-movement desynchronization, whereas it affects the post-movement synchronization on background rhythms.