Direct Responses to Hippocampal Stimulation in the Rabbit

Abstract

Responses to direct electrical stimulation were recorded at various depths in the hippocampus of the rabbit, and three types of response were distinguished according to the layers stimulated.
1. The first type of response was a spike potential evoked by stimulation at a level 0-0.2mm. beneath the ependyma. This potential may be divided into two subtypes. One was a small fast spike of about 1 msec. duration recorded at the superficial layer of the hippocampus and the other was a slow negative spike of about 2-3 msec. duration recorded most clearly at a depth 0.4-0.6mm. beneath the ependyma.
2. The second type was a slow wave evoked by stimulation at a level 0.2-0.4mm. beneath the ependyma. The wave was negative de-flection at the superficial layer of the hippocampus, and phase reversal occurred at a depth of about 0.7mm.
3. The third type was a slow wave with a spike-like potential evoked by stimulation at a level 0.6-1.0mm. beneath the ependyma. The slow wave showed a positive negative sequence at the ependymal surface and negative deflection beyond a level 0.7mm. beneath the ependyma. The negative spike-like potential superimposed upon the wave had a maximal amplitude at about 0.7mm. depth.
4. The electrophysiological and pharmacological properties of the three types of response were investigated, their relation to the structure of the hippocampus was discussed, and the following conclusion was reached: The fast spike originates in nerve fibers in the alveus, while the slow spike and spike-like potential represent mainly activity of somata of pyramids. The close similarity of the slow wave to the so-called dendritic potential of the neocortex was pointed out.