Scientists from the Boston University Center for Systems Neuroscience (MA, USA) have investigated the power of smell to preserve memories of fear in mice for an extended period of time.
These findings have recently been published in Learning and Memory and could lead to further developments of treatments for memory-related mood disorders, such as post-traumatic stress disorder.
Memory formation has always been a mysterious field and the mechanisms behind the making of memories are still not understood well. System consolidation theory is regarded as the most accepted theory explaining how memories form. It suggests that memories are first processed by an area of the brain called the hippocampus.
Over time, the cells containing those memories reorganize and the memory is processed by the prefrontal cortex at the front of the brain. During this transformation, many memories are lost or faded.
This traditional theory has faced criticism over recent years. Why are people still able to vividly recall memories made years ago and why are these memories often triggered by scents?
Boston University neuroscientist Steve Ramirez set out to answer these questions. Memories of fear were created in mice by performing a series of harmless electric shocks. Half of the group were simultaneously exposed to the scent of almond extract, while the other half were not.
On the next day, the procedure was repeated at a recall session during which no electric shocks were given, but half the mice were once again exposed to the almond extract scent. Both groups of mice exhibited activation of the hippocampus region of the brain, suggesting they had recalled the shocks they were given the day before. These findings were consistent with system consolidation theory.
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When the recall session was repeated 20 days later, mice that had not been exposed to the scent showed an activation of the prefrontal region, but in mice that had been exposed to the scent, significant brain activity was still seen in the hippocampus region.
Using these results, Ramirez explains that: “Odor can act as a cue to reinvigorate or reenergize that memory with detail.” While questions remain about the exact role of smell in memory processing, the results of this study can begin to pave the way for investigations into drug-based post-traumatic stress disorder treatments, which usually act by attempting to remove traumatic memories.
Sources: Grella SL, Fortin AH, McKissick O, Leblanc H, Ramirez S. Odor modulates the temporal dynamics of fear memory consolidation. Learn. Mem. 27, 150–163 (2020); www.bu.edu/articles/2020/its-true-scent-really-does-have-power-over-memory/