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Stanford researchers develop technique to trace neural pathways across the brain

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It's common knowledge that our sense of smell enhances the taste of foods, enriches appreciation of the outdoors and warns of certain dangers, such as fires. Still, not much is known about the ways in which our brain processes smell.

So, using mouse models, Stanford researchers and colleagues devised a method to map the path that scent signals take from the olfactory bulb, the area of the brain that receives signals from odor receptors on the nose, to higher centers of the brain where processing takes place. A paper describing the new technique, which makes it possible to map long-distance nerve connections in the brain, was recently published online in Nature.

An article in today's Stanford Report explains the researchers' findings:

They found that most of the nerve pathways heading to the higher processing centers that direct the mice's innate like or dislike of certain odors, and trigger a response to them, originated from one region - the top part of the olfactory bulb. This could explain how the mouse brain directs the animal's innate fear response to cat or fox urine.

This is in contrast to the neurons heading to the brain areas which process learned responses to odor. The neurons associated with learned responses are scattered all over the olfactory bulb, and their relative lack of organization could reflect their flexibility in allowing the mice to learn to avoid or be attracted to new smells.

The group also found that each neuron in the brain's higher centers receives signals from at least four neurons in the olfactory bulb, each of which receives input from a large number of like odor receptors. This progressive funneling and processing helps explain how the brain integrates the information from many different odors, [study author Liqun Luo, PhD,] said.

Photo by Dennis Wong

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