The present study aimed to investigate the effects of cognitive/emotional bias on central nervous odor processing. Forty-five female participants were divided into three groups and were either led to believe the odor was a natural, healthy extract (positive bias), potentially hazardous (negative bias), or a common test odorant (control). The odor (isobornyl acetate) was presented via a constant-flow olfactometer and the EEG was recorded from 60 scalp locations. In the negative bias condition, participants reported reduced well-being and judged the odor as less pleasant. However, neither the thresholds nor the intensity ratings were changed by the context condition. Chemosensory event-related potential (CSERP) analysis revealed that the latencies of the N1 and P2 components were prolonged in the negative bias condition and shortened in the positive bias condition. Current source densities were most prominent in the frontal lobe in negatively biased participants. The findings show that expecting to perceive an emotionally significant odor affects the early encoding of odors.
