Studies on single neurons in dorsal hippocampal formation and septum in unrestrained rats: Part II. Hippocampal slow waves and theta cell firing during bar pressing and other behaviors

Abstract

Hippocampal slow waves and firing of theta cells were investigated during voluntary and automatic behaviors of the rat, including bar pressing on continuous reinforcement and fixed-ratio 50. Voluntary behaviors (walking, orienting, postural adjustments, approaching food or water, following the experimenter's hand, jumping, and exploring) were accompanied by theta in the slow waves and fast, rhythmical firing in the theta cells. For a given cell the rates of firing were similar for all voluntary behaviors. Automatic behaviors (eating, drinking, teeth chattering, grooming, vomiting, and yawning) were accompanied by irregular slow-wave activity and slow, irregular firing in the theta cells. For a given cell the rates of firing were similar for all automatic behaviors. Electrode placement within the hippocampus was critical with regard to how much slow-wave theta could be recorded during voluntary behaviors, whereas theta cells throughout the hippocampus were identical in the form of their firing. Bar pressing on both continuous reinforcement and fixed-ratio 50 gave clearly non-theta responses in both units and slow waves. Some well-learned voluntary behaviors can become automatic and are not in the theta mode.