Biomedical Frontiers: Winter 1995, Vol.2, No.2
How Does the Brain Smell?

Whether a scent emanates from a bouquet, the beach, or fresh-ground coffee, its essence envelops and invades us. Odors penetrate our consciousness, almost against will. Smell by its nature is primal. Our nose is a direct conduit from the environment to our brain communicating pleasurable and offensive sensations that conjure up emotions, thoughts, and memories.

What structure has the brain evolved to distinguish between the smell of a rose and an enticing cologne? Why do we as a species distinguish 10,000 or so aromas? How does what happens in our sensory olfactory neurons get read by the higher cortex to evoke images and feelings?

Dr. Richard Axel, Eugene Higgins Professor of Pathology and Biochemistry and Molecular Biophysics and Howard Hughes Medical Institute investigator, set out to answer these questions. In April 1991, Dr. Axel reported in Cell he had cloned around 1,000 genes for odor receptors, cell surface molecules on neurons in the nose that could theoretically bind everything from jasmine to turpentine.

This gene family of transmembrane receptors represents the largest percentage of the genome dedicated to a single physiological function. "We use one in 100 of our genes to recognize smells," says Dr. Axel. Although the very number of odor receptor genes partially explains how humans recognize a multitude of odors, it is not the whole picture. Recently, Dr. Axel and his laboratory have begun to understand more about the neural physiology of olfaction.