Hippocampal Electrical Activity and Behaviour in Rabbits during Adaptation to a Novel Semi-Natural Environment

The aim of the present experiment was to show possible modifications in behaviour and hippocampal electrical activity during adaptation to a novel semi-natural environment. Rabbits with chronic implanted electrodes in the hippocampus were introduced into a large, natural, open-air enclosure. Their spontaneous behaviour was studied for 3 days. Electrical activity was recorded by telemetry, stored with behaviour on a video-tape, and then analysed. Behaviour was divided into categories and variables. The categories were: activity directed towards the environment (including exploratory movements, scanning, marking, etc.) and self-directed activities (such as eating, drinking, self-grooming, etc.). Exploratory elements were observed and classified according to a spatial and a temporal criterion. The rabbits showed a progressive adaptation to the environment with quantitative and qualitative reduction in exploration and an increment in quiet immobility and inspective activities. Three EEG patterns were recognized from autocorrelation and spectral analysis: high rhythmicity theta (HRSA) with specific relationship to voluntary movements, such as exploration and running; low rhythmicity theta (LRSA) in signalling activities or self-directed behaviour and during postural and reactive immobility; and irregular activity (IA) sometimes seen in the same immobile behaviour. The results show that some behaviours (exploration, alert and postural immobility, self-directed activity) are correlated to specific patterns of electrical activity in the hippocampus and, as exploratory behaviour decreased with time, there was a concomitant increase in EEG frequency.