Differential patterns of activation of the pyramidal system elicited by surface anodal and cathodal cortical stimulation.

Abstract

The effects of opposite polarities of focal stimulation of the surface of motor cortex of cat on the pyramidal tract population response (Direct and Indirect wave) were investigated. The Direct wave (surface anode) was evoked at lower stimulating intensities, unaltered by repetitive stimulation, resistant to the effects of asphyxia, facilitated by anodal and depressed by cathodal polarization. In contrast, the Direct wave (surface cathode) was elicited at higher stimulating intensities, potentiated by repetitive stimulation, abolished by anoxia, facilitated by cathodal and depressed by anodal polarization. The 1st Indirect wave component (surface cathode) was elicited at lower stimulating intensities, readily potentiated by repetitive stimulation, facilitated by cathodal and depressed by anodal polarization. The 1st Indirect wave (surface anode) was elicited at higher stimulation intensities, potentiated by repetitive stimulation with greater difficulty, facilitated by anodal and depressed by cathodal polarization. It was suggested that pyramidal tract responses evoked by opposite stimulating polarities have a different origin in motor cortex.