Early olfactory event related potential can represent odor habituation

Abstract

Habituation is a process showing a decrease in response to a stimulus after being repeatedly exposed to it. To study habituation, measurement of event-related potentials (ERP) has been widely used in the olfactory system as well as other sensory systems. According to previous odor habituation studies, ERP near 200–700 ms was mostly studied. However, several studies showed that odor signal in the central nervous system (CNS) processed earlier than 200 ms. For these reasons, we studied whether early olfactory ERP within 200 ms may be changed during odor habituation. To verify the change of early ERP during odor habituation, we performed an odor habituation behavior test and EEG experiments. The experimental procedure was consisted of three steps. In first step, odorants or distilled water were offered continuously during 30 s. Next, one of two odorants was offered during 2 s for measurement. Last step was 30 s of rest period. There were three different conditions for studying odor habituation: ‘none’ (distilled water offered in first step), ‘different’ (two different odorants offered in first and second step) and ‘same’ (the same odorant offered in first and second step). The perceived intensity was significantly decreased under the same condition compared to those under other conditions in the behavior test. In accordance with behavior results, we found channels showing significantly different ERP amplitude across the conditions and significantly correlated with the behavior test within 200 ms. These results suggest that early ERP signal of the brain may be involved in odor habituation as other sensory systems, and that odor habituation was processed differently depending on brain areas. Our studies suggest that odor habituation may be represented by the change of early negative potential in the brain and these processes may be different depending on brain areas.