Summer 1995 Volume 4, Number 3

But how do we perceive the difference? Kerry Ressler of Linda Buck's laboratory at Harvard Medical School reports that, using odorant receptor genes to probe the mouse olfactory system, Buck and her colleagues have made progress in understanding this question.

In the nose, each olfactory neuron contains only one of the hundreds of different receptor types available, and each specifically recognizes different odorants -- translating the chemical signature into an electrical signature from the neurons that recognized the odorant.

But neurons of the same receptor type are mingled with millions of neurons of different receptor types. How can the brain interpret this resulting mosaic of activity? How does it "know" what the nose is smelling? It seems to simplify the task by refining the distributed neuronal inputs: For example, axons from thousands of scattered rose-specific neurons may go to only a few selected sites (out of thousands of possible targets) in the brain. Hence, the smell of a rose is perceived when only a small number of specific sites within the brain structure called the olfactory bulb are activated -- a unique pattern of activity, different from patterns sparked by the smell of skunk or any other odor.

The findings have been causing a stir among brain researchers lured by the scent of how information is represented in the brain.