Gamma and beta oscillatory signatures of the human olfactory bulb encode odor valence and sampling

As the first relay between peripheral and central olfactory systems, the human olfactory bulb (OB) plays a dynamic role in odor perception. This study investigated OB time-frequency responses to odors of different valences under active versus passive sampling. Thirty-two participants underwent either inhalation-synchronized (active) or respiration-independent (passive) odor stimulation while electrobulbogram signals were recorded. Across both sampling modes, OB activity followed a consistent sequence of early gamma, scattered beta bursts, and late gamma-beta oscillations. Active sampling induced stronger and more widespread gamma activity throughout processing. Participants were further grouped based on N1-P2 ERP amplitudes. ERP-sensitive individuals exhibited enhanced early low-beta OB activity, whereas ERP-insensitive individuals showed stronger mid-to-late gamma and beta responses, suggesting compensatory stimulus re-evaluation. These findings indicated that OB gamma and beta oscillations encoded odor valence while reflecting temporal processing differences shaped by sampling strategy and individual sensitivity, highlighting the flexibility of early-stage human olfactory processing.