April 17, 2014

Remembering That Smell

Alas, poor sense of smell, I knew you well.

My sense of smell is pretty much dead. I killed it. I killed it by working first in a hog farm while still in high school, then later at various group homes where I was in regular close proximity to… well, lets just call it the “stinkier” aspects of the job, and now I live only a mile or so away from a rather large production factory that has a smelly reputation. Thanks to all of that, I have a very high tolerance for smell. So much so that often times I fail to notice scents that others claim are actually quite strong. Still, every so often I find myself confronted with a scent that triggers a memory. The scent of the soy bean harvest triggers memories of growing up on my grandparents’ farm, different foods trigger memories of when I was younger, having dinner with my mother, the smell of hogs triggers… let’s just not talk about that, and so on. Everyone gets these scent-induced memory triggers from time to time, as our sense of smell is strongly tied to memory, but until now we have had little understanding of just how it works.

Researchers at the Kavli Institute for Systems Neuroscience have recently found the process behind this. Through various tests, they discovered that the brain connects smell to our memories through an associative process in which various neural networks are all linked through synchronized brain ways of 20-40 Hz. They did so by designing a maze for lab rats in which the rat would come to a hole that they could poke only their noses through. When they would do so, they would be presented with one of two smells. One smell would indicate to the rate that food would be found in the left food dish behind the rat while the other scent would indicate it would be in the right cup. Over time, the rats would learn which scent led to which food dish and, after weeks of training, the rats were able to chose correctly more than 85% of the time. Once this was established, the researchers inserted 16 electrode pairs into the hippocampus and into different areas or the entorhinal cortex. What they found was that that after associations between smell and place were established, they saw patterns of brain wave activity – the electrical signal from a number of neurons – during retrieval of the food reward. When the rats were exposed to the smell, there was a notable burst of activity of 20 Hz waves in a connection between an area in the entorhinal cortex, laternal entorhinal cortex (LEC), and in distal CA1 (dCA1) which is an area in the hippocampus. The 20 Hz activity in these areas grew in parallel with the rat’s learning while there was little coherence between these areas of the brain when the training began. When ti was over, cells were locked in place to the oscillation and many of them responded specifically to one or the other smell-odor pairs.

And that is it. The signals you get from your nose are connected to memories, each of which connects to a different location that has been pinpointed onto your brain’s inner map of your life. So, the next time you breathe in a familiar scent, see what memories come to mind.

Image Credit: Thinkstock

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