The Current Status of Evaluation Technologies for the Function of Human Olfaction

The sense of smell is one of the essential tools for all living things to survive. For example, it enables them to escape from danger in advance or find food to sustain life [1,2]. For human beings, it also has been crucial function for better quality of life. There has been a recent increase in diseases associated with olfactory dysfunction as shown in Fig. 1 [3]. Moreover, because many patients with olfactory dysfunction have often complained of their olfactory functions as well as reported of chronic pain, olfactory dysfunction must not be neglected anymore [4]. In addition, the olfactory function has been considered to be one of the biological markers associated with various diseases, such as Alzheimer’s disease [5], Parkinson disease [6], multiple sclerosis [7], and brain tumor. Thus, the evaluation of olfactory function will shed some light to understand the function of the human olfactory system as well as assess the olfaction value in day-to-day life [2]. The methods for assessing the olfactory function are largely divided into electrophysiological and psychophysical methods. The psychophysical inspections such as University of Pennsylvania Smell Identification Test (UPSIT), The Sniffin’ Stick, and T & T Olfactometer [7-9], are methods mostly based on questionnaires or simple apparatus. Normally, the evaluator presents a fragrance and then evaluates subjectively the subject’s awareness of smelling, whereas the electrophysiological tests evaluate olfactory function based on objective measurement such as biosignals and medical imaging. In this paper, we review the overall evaluation methods of olfactory functions and suggest complementary points to improve conventional technologies.