Odor induces characteristic time courses of theta, beta and gamma oscillations in human olfactory cortex

Neuronal oscillations are fundamental to cognition, facilitating coordination and communication of information within and across brain regions. Studies on the spectral and temporal dynamics of oscillatory rhythms have contributed substantial insight to our understanding of mechanisms of human visual, auditory and somatosensory perception. However, these oscillations have been largely unexplored in the human olfactory system, where we lack basic understanding of fundamental spectrotemporal and functional properties. Determining if and how dynamic signatures of neural activity occur in human olfactory cortex is critical to understanding how we process odors. Here, we establish a characteristic oscillatory response to an odor in the human brain. Using direct electrical recordings from human piriform cortex, we identified three key odor-induced rhythms, in the theta (4-8Hz), beta (13-30Hz) and gamma (30-150Hz) frequency bands, each with distinct functional and temporal properties. While theta emerges and dissipates rapidly at the start of inhalation, beta and gamma emerge later, with beta persisting through exhalation, and gamma peaking around the transition between inhalation and exhalation. Beta and gamma amplitudes strongly predict odor identification ability, whereas theta does not. Theta phase modulates beta and gamma amplitudes during inhalation, only when odor is present. Our findings establish that smells elicit distinct neuronal rhythms in human olfactory cortex, which are dynamically interplayed over the course of a sniff. Our data further suggest a fundamental role for beta and gamma oscillations in human olfactory processing, and that their amplitudes--organized by theta phase--subserve odor identification in humans.