How Do Certain Smells Bring About Special Memories?

Coordination between the areas of the brain responsible for memory and smell allow us to remember an event when we smell something familiar later on. Photo courtesy of Shutterstock

The researchers set out to determine how the two neuronal pathways — for smell and memory — converged to create these unique memories. They fitted a group of mice with electrodes on their hippocampus and different parts of the entorhinal cortex, both of which are involved in memory consolidation, with the latter also being responsible for receiving input from the senses. They then had the mice run through a maze containing holes big enough for their noses to peak through. When they smelled what was on the other side, they were given two different smells, of which one told them the direction that food was in. After three weeks, 85 percent of the rats were able to determine, based on smell and memory, where to go for a reward.

They found that the more the rats became familiar with the maze’s purpose, their brain waves began to synchronize. “Immediately after the rat was exposed to the smell there is a burst in activity of 20 Hz waves in a specific connection between an area of the entorhinal cortex, lateral entorhinal cortex, and an area in the hippocampus,” called distal CA1, Igarashi said in the statement. The same activity was not seen at a comparable strength anywhere else in the brain.

Igarashi K, Lu L, Colgin L, et al. Coordination of entorhinal–hippocampal ensemble activity during associative learning. Nature. 2014.