HIPPOCAMPAL ELECTRICAL-ACTIVITY IN RABBITS DURING EXPLORATION OF A SEMINATURAL ENVIRONMENT

The hippocampal EEG shows characteristic profiles during different beh avioural items. A class of hippocampal neurones is active when the ani mal is in specific places of an environment (place units). However, th ere are only a few neurones and the role of the hippocampal EEG in spa tial information processing remains to be explained. In the present ex periment we studied the exploratory behaviour of rabbits (implanted wi th chronic electrodes in the hippocampus) in an open-air, semi-natural environment. Hippocampal EEG was recorded by telemetry and related to exploratory behaviour by superimposition onto video. Six rabbits were introduced singly to the semi-natural environment and each remained t here for 3 days. Their behaviour and EEG was analysed for three 30 min sessions (at 0, 6 and 56 h). Exploration was the main behaviour in th e first observation and decreased progressively in the following sessi ons. The environment was divided into three zones which were explored differently through time. The hippocampal EEG, recorded during explora tion, presented an increase of frequency from the first to the second observation. However, since EEG frequency increased when the animal ex plored the central area of the enclosure. a response in the place doma in cannot be excluded. (C) 1997 Elsevier Science B.V.