Researchers at Stanford have traced the path that scent takes from nose to brain, for the very first time. In order to find the connection, they actually reverse engineered the pathway, beginning in the brain and backtracking to the olfactory bulb.
Scientists injected two viruses into mouse brains. The first one, a low-grade virus, cleared the way for the other virus to go from the higher centers in the brain, down the connections to the olfactory bulb. They found that most of the nerve pathways connected to the parts of the brain that determined the mice’s like or dislike of the smell originated from the top part of the olfactory bulb. The concentration of neurons there allows a quick reaction when the mouse is exposed to “bad” smells, such as the scent of a predator.
There are also other neurons from all over the olfactory bulb, which are connected to brain areas that process learned responses to odor. Researchers postulate that their scattered locations allow the mice to have “flexibility in learning to avoid or be attracted to new smells.”[1]
They also discovered that each neuron the brain that receives scent information is connected to at least four neurons in the olfactory bulb, each of which receives input from multiple odor receptors. This is how the brain integrates and makes sense out of a number of different smells.
[1] “The Brain Knows What the Nose Smells, but How? Standford Researchers Trace the Answer,” Stanford University News Service, February 2, 2011, by Sandeep Ravindran
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