Near-infrared spectroscopy of orbitofrontal cortex during odorant stimulation.

BACKGROUND For olfaction, several studies have reported near-infrared spectroscopy (NIRS) signal changes in the orbitofrontal cortex (OFC) during odor stimulation. However, the roles of human OFC in olfactory cognition are less well understood. This study was designed to better understand the roles of OFC for olfaction. METHODS Hemodynamic responses for phenyl ethyl alcohol or citral in the OFCs were measured with NIRS. After the experiment, participants were asked to describe the characteristics of the odor and to rate odor intensity and hedonic valence. RESULTS Statistical analysis of all participants' data showed significant changes in the concentration of total hemoglobin in the left OFC during the trial (p = 0.04). The total hemoglobin signal increased significantly in the right OFC (p = 0.0008) of the participants who successfully identified the odorant stimulus. CONCLUSION Our findings showed that NIRS combined with a questionnaire is a useful method for studying the functional neuroanatomy of OFC in terms of olfaction.