Nasal Cavity Brain Olfactory Bulb Olfactory Bulb Olfactory Epithelium Vomeronasal Organ

tive sense. In Marcel ProustÕs novel Remembrance of Things Past, the nostalgic ßavor and fragrance of a madeleine, a delicate pastry, evokes a description of taste and smell, the senses that Òalone, more fragile but more enduring, more unsubstantial, more persistent. . . bear unßinchingly, in the tiny and almost impalpable drop of their essence, the vast structure of recollection.Ó Humans often view smell as an aesthetic sense, yet for most animals smell is the primal sense, one they rely on to identify food, predators and mates. Indeed, for many organisms, odors are their most efficient means of communicating with others and interpreting their surroundings. Innate behavior in response to smell is essential to these organismsÕ survival and most likely results from nonconscious perception of odors. Each individual has a unique, genetically determined scent. This olfactory identity is coupled with a remarkable ability to distinguish a diversity of odors. Humans, for instance, can recognize approximately 10,000 scents, ranging from the pleasurable scent of freshly cut ßowers to the aversive smell of an angry skunk. Many animals have an even greater sensitivity to odors than humans do: bloodhounds, for example, are legendary for their extraordinary ability to discriminate scents. The wide spectrum of odors that humans consciously detect prompt varied emotional and cognitive responses. But do humans recognize other smells without a conscious awareness of this perception, and do such odors elicit innate behavioral responses? How does the perception of speciÞc odors lead to appropriate thoughts, memories and behaviors? Whether smell is primal or aesthetic to a species, all organisms must have developed in the course of evolution mechanisms to recognize various odors and transmit this olfactory information from the nose to the brain, where it is decoded to provide an interThe Molecular Logic of Smell