Persistent odors induce hedonic valence-independent alpha and beta wave EEG desynchronization

While electrophysiological responses to olfactory stimulations are widely investigated using electroencephalography (EEG), studies on odor perception often yield inconsistent results. In this work, both early and late olfactory event-related potentials (ERPs) from fifteen healthy participants during sustained presentation of odors were investigated. A custom-designed olfactory stimulation system synchronized with a high-density EEG was used to deliver pleasant, unpleasant and neutral odors during an eyes-closed, non–sniff-locked olfactory stimulation protocol. Both pleasant and unpleasant conditions elicited heightened early ERP amplitudes, compared to the neutral odor, with N40 peaks localized in the occipital region. Presenting the olfactory stimulus continuously for 6 s significantly reduced late ERP global field power, revealing prolonged and spread cortical desynchronizations, particularly in the frontal, central and parietal regions, and especially in the alpha and beta bands. This occurred for both the non-neutral stimulation conditions (pleasant and unpleasant), relative to the neutral one, regardless of their hedonic valence. These findings indicate that cortical responses to olfactory stimuli are manifested by initial occipital sensory gating, followed by persistent and widespread alpha/beta desynchronizations, independently of odor valence.