Hippocampal EEG and behavior: changes in amplitude and frequency of RSA (theta rhythm) associated with spontaneous and learned movement patterns in rats and cats.

Slow electrical activity was recorded from the dorsal hippocampus in rats during running in a motor-driven wheel, swimming, conditioned avoidance (running, jumping), lever pressing for food and sleep, and in cats during walking in a treadmill, eating and lapping milk. Large-amplitude clear rhythmical slow activity (RSA) was recorded from the hippocampus proper and smaller amplitude RSA and fast activity was recorded from the dentate gyrus-CA 4 area. This was also observed in acute rat preparations. During large movements (run, jump) RSA amplitude was up to 6 times greater than during small movements (head turn, lever press). Initiation of movement was associated with an increase in RSA frequency, which was most pronounced with forceful movements. During steady running or swimming in the rat frequencies of 7-9 Hz were recorded and during prolonged running up to 8 hr RSA was unchanged. RSA frequency did not vary with the speed of steady running or steady locomotor patterns of swimming, walking, trotting or galloping. RSA frequency and amplitude may reflect different mechanisms; frequency was normal after hippocampal electrographic seizures, amplitude was depressed; frequency varied directly with core temperature (27-42 ° C) but amplitude remained constant. Increases in RSA frequency and amplitude during paradoxical sleep were associated with muscular twitches, suggesting that forebrain motor mechanisms were activated. The results are interpreted in support of the idea that RSA is related to higher level control of voluntary movement.