Bioelectrical activity of isolated cortex—II. steady potentials and induced surface-negative cortical responses

Abstract

Monophasic, surface-negative responses evoked by combined low- and high-frequency shocks to the cerebral cortex of cat were obtained from both intact and isolated cortical tissue. The steady potential level at the cortical recording site was found to be 300–500 μV negative to frontal bone when the responses were evoked. Cortical polarization with currents of 2–10 μA yielded similar steady potential levels, and, when substituted for the original high-frequency shocks, also evoked the responses from both intact and neurally isolated cortex. Many times, when evoked inside isolated slabs, the responses retained their original rate when the frequency of the driving stimulus was lowered. These results suggest that shifts of steady potentials probably served as the agent for ephaptic transmission across the cut.