Changes in the amplitude of hippocampal evoked potentials during avoidance behaviour in the cat.

In seven cats changes in the hippocampal EEG and in the hippocampal evoked potentials (EP-s) produced in Ca-1 field by stimulation of the contralateral hippocampus, ipsilateral hippocampus and entorhinal cortex were investigated during a conditioned, active avoidance response (AAR). The highest amplitudes of the EP-s were observed before the CS (conditioning stimulus) onset, when the animal was relaxed and an irregular activity of variable amplitude and frequency, dominated in the hippocampal EEG record. The lowest amplitudes were recorded during performance of the conditioned locomotor response, associated with a rhythmic, slow activity (RSA) or, occasionally, with a small irregular activity (SIA) in the hippocampal EEG. The course of changes in EP amplitude during trials might be expressed in the form of an U-shaped curve. The data suggest that changes in the hippocampal EP-s and in the hippocampal EEG are due to changes in the intensity of the same unspecific process.