Why does your sense of smell trigger memory?

Posted by Chelsea Voge on

Despite the tendency for us humans to underestimate the power of smell, the animals need it more and thus their level of sense of smell is well developed. Dogs, for instance, are a good example of how olfaction is paramount to animals as they need it for survival. In the past when the human was still in the Stone Age, sense of smell was important. The dogs can find food, communicate and even reproduce all because of their powerful sense of smell. The sense of smell is represented in the oldest part of the brain, and that explains why we can trigger strong memories because of smell. Most of us have experienced flashback after encountering a certain smell or fragrance. Some people have compared smells to souls because it is the only thing that can remain after everything else is gone.

The reason as to why smell trigger memories are because scientists have identified a part of the brain, the amygdala and the hippocampus responsible for memory to have a strong connection with the olfactory cortex, part of the brain responsible for processing olfactory information. Compared to other senses olfaction is the slowest and has its receptors in the nose. Olfaction also has a close association with emotions as it forms part of the limbic system of the brain. This part is mainly responsible for the emotions we perceive. Additionally, the smell has a close association with taste.

To understand this, odor molecules produce chemicals that are absorbed in the nasal passage and binds to receptors of the epithelium of the nose. This then triggers a message that is sent to the brain, the olfactory bulb. The signals are then transmitted to the brain, limbic system, for processing and saved as a memory in the limbic system depending on its importance according to the individual’s experience. Some information is also relayed to the sensory cortex of the brain to create the sense of flavor.

Another reason why memory triggers memory is that emotions are involved in memory retrieval. Therefore, this means smell alone cannot trigger a memory; it needs to be linked with emotion. This is what happens when brain encounters new scent. Our brain forges a link between the smell and a memory associating the smell of chlorine with summers at the pool or lilies with a funeral. When you encounter the smell again, the link is already there, ready to elicit a memory or a mood. Chlorine might call up a particular pool-related memory or only make you feel content. Lilies might agitate you without your knowing why. This is part of the reason why not everyone likes the same smells.

Separate research done had also revealed that both young and senior adults could remember more than twice as many memories when they were associated with an odor, which according to researchers provides evidence for strong olfactory cuing that is remarkably intact in old age. Both positive and negative relationships and memories are brought back by different odors. For instance, fragrances are known to induce physiological arousal and trigger trauma-related memories.  Therefore, they are also thought to play a major part in triggering sad memories in individuals with post-traumatic stress disorder (PTSD).

Intriguingly, a mother’s fears may even be passed on to her child through scent. For example, in one study, female rats were exposed to fear the scent of pepper before they were pregnant. Later, the rats’ pups were exposed to the pepper smell along with a scent of their mother’s reaction to the pepper odor. The newborn pups learned to fear the smell even when their mothers weren’t there, after just a single exposure. Blocking the activity of the amygdala, a region of the brain that processes emotions, including fear responses, the newborn rats did not learn to fear the peppermint scent.

So it seems that, through scent, infants can learn from their mothers about potential environmental dangers before their sensory and motor growth allows for them a comprehensive exploration of the surrounding environment. The impact of scent on fear was very high that during the study, it was observed that some of the rats tried to plug the tubing to stop the odor from coming in, a habit that the researchers plan to study further.

Interestingly, different species have a different amount of receptors, each identifying several odors and the receptors are replaced every 60 days. Despite our line of thought that vision and our audition are the most important senses, smell also plays a crucial role in our survival. For instance, through our sense of smell, we can detect poison and edible food. Thus, though primitive, it is an important role that the brain executes.

In conclusion, smell triggers memory after association with emotions due to the complicated wiring between the limbic system and the olfactory cortex. This idea can be explored by researchers and be used in aromatherapy.