Optical recording of the intrinsic signal from the human olfactory cleft.

Endoscopy of the human olfactory cleft is important for both research in human olfaction and clinical examination with regard to olfactory disorders. However, endoscopy only provides information on the morphology and functional status of the epithelium, and it does not allow discrimination between respiratory and olfactory mucosa. To obtain information on the functional status of the olfactory mucosa, I used endoscopy to investigate the optical intrinsic signal recording from the human olfactory cleft. A light-emitting diode (617 nm) light source and a cooled charge-coupled device camera were prepared for endoscopy of the olfactory cleft. Subjects were exposed to various odors presented in front of their nostrils. In addition, blanks were used for control. When normosmic subjects sniffed the odors, the intensity of the signal from the olfactory mucosa changed, which was not the case when blank stimuli were presented. Different odors activated different response patterns. A decrease of the oxyhemoglobin level in the activated olfactory epithelium is suspected to be responsible for this observation. The optical intrinsic signals were recorded from the human olfactory cleft with an endoscope. This technique may be applicable to basic research in olfaction and to a clinical test for the assessment of olfactory disorders.