Further characterization of cortical polarization-induced motor behavior in rabbits

Anodal direct currents of 1 or 10 microA were unilaterally applied for 30 min once a day to the premotor area of the cerebral cortex in rabbits, in which the current application was repeated 10 times at intervals of 2-3 days. Peripheral motor behavior was observed during and after each polarization trial, and was compared with that before polarization. The motor manifestations were classified into two types: gentle flexion of either forelimb and struggle with violent movement of forelimbs. Flexion of the forelimb contralateral to the polarized cortical side was clearly increased by polarization at an intensity of 1 microA, but not at 10 microA. Forelimb struggle of both sides decreased only when 10 microA was applied. These results suggest that the passage of 1 microA current activates the polarized local area of the cortex, while 10 microA has an inhibitory effect on cortical activity.