Slow negative cortical potential preceding the onset of postural adjustment.

We investigated whether a cortical potential exists, that is similar to the Bereitschaftspotential, preceding postural adjustment followed by voluntary ballistic rising on tiptoe in 10 healthy subjects. On the basis of the electromyogram (EMG) activities of the soleus muscle, the onsets of the premotion silent period (PMSP) and EMG discharge were determined. The negative potentials associated with a voluntary rise-on-tiptoe movement with respect to EMG onset were similar to the readiness potential associated with voluntary foot movement. The slopes of the slow negative potential associated with the PMSP onset were significantly more negative than those of the potential associated with rise-on-tiptoe movement, particularly over the frontal electrode positions. The results suggest that a cortical potential precedes postural adjustment that is followed by voluntary rising on tiptoe.