Sensation and perception consist of five major modalities: vision, auditory, olfactory, gustatory, and somatic sensory systems. These sensory systems perceive information from the external environment through peripheral neurons that express specific sensory receptors and transmit the information to the central nervous system. The olfactory system could be divided into two categories: the main olfactory system that perceives odorous chemicals, which tend to smell, and the accessory olfactory system that detects pheromones, which are chemical signals that convey information about sex and strain. Unlike visual and taste systems, the olfactory system has acquired highly discriminative capabilities to distinguish thousands of different odorants and specie-specific pheromones.We herein discuss about several issues that have extensively been studied in the field of olfactory research, and review recent progresses including ours. Molecular bases for odorant recognition by olfactory receptors will be described by Sayako Katada. How we perceive an odorant mixture will be the matter of topic discussed by Yuki Oka. Recent progresses in olfactory sensory adaptation will be provided by Aya Kato. Function of olfactory receptors in non-olfactory tissues such as in sperm will be presented by Dr. Nanaho Fukuda. Odorants that possess psychological and endocrinological effects will be introduced by Mika Shirasu. The nature of mammalian pheromones will be discussed by Dr. Hiroko Kimoto. Molecular biology of pheromone receptors will be reviewed by Sachiko Haga. Mechanisms underlying insect sex-pheromone perception will be described by Takao Nakagawa. Olfaction in fish will be presented by Dr. Koji Sato. Plant talk via odorants will be introduced by Satoko Hosokawa.
All the topics that are focused in this special issue have been subjects of our research direction. The hope is that unraveling the mystery of the sense of smell will lead to rediscovery of the importance of olfaction, which has always been undervalued, along with the almost pathological avoidance of smells in modern human society, and ultimately will result in helping human welfare.

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