Via Scientific American

In the recent study, the natural memory was formed by training mice to associate a specific odor (cherry blossoms) with a foot shock, which they learned to avoid by passing down a rectangular test chamber to another end that was infused with a different odor (caraway). The caraway scent came from a chemical called carvone, while the cherry blossom scent came from another chemical, acetophenone. The researchers found that acetophenone activates a specific type of receptor on a discrete type of olfactory sensory nerve cell.

They then turned to a sophisticated technique, optogenetics, to activate those olfactory nerve cells. With optogenetics, light-sensitive proteins are used to stimulate specific neurons in response to light delivered to the brain through surgically implanted optic fibers. In their first experiments, the researchers used transgenic animals that only made the protein in acetophenone-sensitive olfactory nerves. By pairing the electrical foot shock with optogenetic light stimulation of the acetophenone-sensitive olfactory nerves, the researchers taught the animals to associate the shock with activity of these specific acetophenone-sensitive sensory nerves. By pairing the electrical foot shock with optogenetic light stimulation of the acetophenone-sensitive olfactory nerves, the researchers taught the animals to associate the two. When they later tested the mice, they avoided the cherry blossom odor.

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