Olfaction

Abstract

This chapter provides an overview of the human olfactory system, beginning with the peripheral receptor neurons in the nasal cavity and the first relay in the olfactory bulb. The projections of the olfactory bulb to the primary olfactory cortical areas are described in macaque monkeys, and the comparable olfactory areas in the human brain are described. It is noted that humans are generally considered "microsmatic," with a relatively poorly developed olfactory system compared to that of "macrosmatic" mammals. Indeed, the structure and lamination of the olfactory bulb and primary olfactory cortex are not as well-defined in humans as in rodents and carnivores. Further, the olfactory structures certainly do not make up as large a fraction of the forebrain in humans as in rats and cats. However, almost all the major olfactory structures found in rats are also present in humans, and in absolute terms the human structures are far from rudimentary. Finally, olfactory projections to the hypothalamus, thalamus, and frontal cortex are discussed, based on experimental work in monkeys and on functional imaging studies in humans. © 2004 Elsevier Inc. All rights reserved.