The study of odor adaptation in human brain revealed by olfactory event-related potential

Abstract

Odor adaptation is the decreased intensity perception of an odor when the odor is continuously offered. Odor adaptation has important roles in our daily life, such as desensitization for unpleasant odors or odor discrimination from background odors. Even though the importance of the odor adaptation, our understanding of odor adaptation in central nervous system remain unclear. According to previous studies, odor adaptation is related to the decreased activation of olfactory receptor neurons (ORNs) in the olfactory epithelium (OE). However, there are less evidences how this reduced signal process in the brain. Therefore, we focus on how odor adaptation processes in central nervous system.

To understand the central processing of odor adaptation, we performed EEG experiments to analyze event-related potential (ERP) N1 component. N1 is one of the widely studied components of the ERP studies. N1 is known as represent processing of exogenous stimulus in dependence on the endogenous state and altered when stimulation intensity is changed. In odor stimulation, N1 is changed depending on odor concentration. For these reasons, we focused on how N1 is related to odor adaptation. We used geraniol for odor stimulation. We set three different pre-stimulation conditions: geraniol, 2-acetlypyrazine and distill water. Geraniol is odor adaptation condition and other two are control conditions. We set 15 sec for pre-stimulations, 2 sec for odor stimulation, then 30 sec for rest period.

Interestingly, in the adaptation condition, the decreased amplitude of the N1 is observed than the amplitude in the control conditions. These results related with behavior results that the intensity perception of geraniol is decreased than the perception of other two conditions.

These findings suggest that odor adaptation may also reduce responses of olfactory processing in the brain and these processes may be represented by the change of N1 component.