What is the significance of gamma wave activity in the pyriform cortex?

The relations between behavior, olfactory input and bursts of gamma wave activity (roughly 30-90 Hz) in the pyriform cortex were studied in freely moving rats. Olfactory input was measured by recording the negative (depolarizing) potentials which occur in the olfactory mucosa during inspiration. Low levels of pyriform gamma activity were associated with spontaneous apnea and slightly higher levels were associated with vigorous sniffing. Intermediate levels of gamma activity occurred during rhythmical breathing during alert immobility, walking, eating, and grooming. High amplitude bursts of gamma activity occurred during very deep breathing during sighing and vocalization. Closing one nostril resulted in the ipsilateral disappearance of pyriform gamma wave bursts, even during vocalization, but contralateral gamma wave activity persisted. It is concluded that pyriform gamma wave activity is entirely dependent on olfactory input and that previously reported relations to conditioning, arousal, motivation, etc., are indirect effects of variations in the pattern of air flow in the upper airway.