Laminar analysis of hippocampal potentials evoked by peripheral stimulation

From areas SA₁ and SA₂ of the dorsal hippocampus of unanesthetized rabbits immobilized with d-tubocurarine a laminar analysis was made of evoked potentials (EP) in response to stimulation of the sciatic nerves. Inversion of the initial surface-positive phase of the EP was observed at the level of the pyramidal layer. The subsequent surface-negative phase reached a maximum value in the layer of basal dendrites of the pyramidal cells. The initial portion was inverted somewhat above the pyramidal layer and reached its maximum value approximately at the boundary of the pyramidal and radial layers. The change in sign of the remaining portion of this component occurred 0.3–0.4 mm deeper than the pyramidal layer. It is suggested that both components of the EP picked up from the hippocampal surface are due to an excitatory postsynaptic potential (EPSP) at the apical (positive phase), and basal (negative phase) dendrites. The positivity in the region of the pyramidal somata appears to be an extracellular reflection of a composite postsynaptic potential (IPSP) generated in this region.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 2, No. 4. pp. 434–438, July–August, 1970.