Hippocampal activity, olfaction, and sniffing: an olfactory input to the dentate gyrus.

Experiments in freely moving rats showed that olfactory stimuli elicit a burst of rhythmical 15-30 Hz waves in or near the hilus of the dentate gyrus but not in adjacent regions of CA1. This fast wave burst is not elicited by visual, auditory, or somatosensory inputs and is not related to motor activity. Electrical stimulation of the olfactory bulb evokes a complex potential in the hilus of the dentate gyrus but not in adjacent regions of CA1. Experiments making use of wave-triggered averaging demonstrated that there is a degree of phase-locking between (a) hippocampal RSA and sniffing or other respiratory patterns, (b) hippocampal RSA and the initiation of jumping, and (c) respiration and the initiation of jumping. An early hypothesis that the hippocampus and dentate gyrus are part of an olfacto-motor mechanism may merit re-examination.