Hippocampal theta frequency shifts and operant behaviour

Abstract

1. 1. A shift of hippocampal dominant theta frequency to 6 c/sec has been demonstrated in the post-reward period in two dogs, which occurs consistently related in time to a well defined behavioural pattern in the course of an operant conditioning paradigm. 2. 2. The frequency shift was detected and quantified by means of sequential and integrated frequency displays and was found to be statistically significant. 3. 3. The occurrence of the hippocampal shift to 6 c/sec became more stable, and the burst of larger amplitude and enhanced regularity, as conditioning proceeded. In respect to the predominance of the component at 6 c/sec a significant difference was found between early and late experiments. 4. 4. A regular pattern of “low voltage desynchronized” hippocampal activity was regularly observed during conditional stimulation, at late stages of conditioning, if followed by correct pressing. When the dog did not perform correctly (inhibition of pressing) there was instead a predominance of theta pattern (peak at 5 c/sec) during stimulation. The difference in contributions of theta rhythm to the total frequency spectra between the two conditions was highly significant. 5. 5. Behavioural correlates of the shift to 6 c/sec and the possible neural mechanisms underlying this phenomenon are discussed.