Your Nose May Be the Key to Your Past

The nose is a sensory organ that is necessary for one of the most, if not the most important senses in human beings and other animals. Without the sense of smell, our world and how we perceive it would be a whole lot different. Smell, also known as olfaction, is crucial for determining not only the food that we eat but also detecting if there is danger nearby, such as a fire. Smell is the only sense that is fully developed in a human fetus before birth. After being born, a child mainly detects and retains many smells they are exposed to and when the child grows up and is exposed to a familiar odor, detailed memories connected to that odor come flooding back. This familiar experience, which is no stranger to many people, is called the Proust effect, and has pushed researchers to delve deeper and to better understand the relationship between smell and memory.

Many researchers are trying to better understand the neuroscience behind how smell can impact memory, and one of those researchers is Laura K. Shanahan. In Shanahan’s lab, she and her colleagues focus on the influence of olfaction on memory consolidation in the brain of a sleeping human. As described in Shanahan’s paper, “Scents and Reminiscence: Olfactory influences on Memory Consolidation in the Sleeping Human Brain”, to better understand the relationship between odor and memory, Shanahan’s lab performs an experiment. Initially, participants are presented with an encoding task, such as matching a specific card with an odor to a location. After the completion of the encoding task the participants are told to go to sleep. The sleep is monitored in an MRI machine and when participants are observed to be in slow-wave sleep, the researchers present the participants with the odors that were involved in the encoding task. Upon waking up, participants were asked tested on the task they had done before sleeping which required them to memorize the card and location to the best of their ability. The results from this experiment showed that the subjects performed a lot better in the memory post-test when they were exposed to the odor stimuli during slow-wave sleep when compared to the results of the memory post-test of subjects who were not exposed to the odor stimuli during slow-wave sleep. The researchers also tried introducing the odor stimuli during other stages of sleep to determine if it had the same result, but they concluded that the memory-enhancing effect only occurred when the stimuli was introduced in slow-wave sleep. Shanahan’s findings have suggested that odors can greatly influence memory consolidation and that the results that came from experiment with sleeping human brain show how strong of a relationship olfaction has with the hippocampus.

In an article titled, “Why smells bring back such vivid memories”, Ana Sandoiu writes about the phenomenon that occurs when a familiar odor is detected and how research regarding the relationship between olfaction and memory can help better understand Alzheimer’s disease. In the article, Sandoiu begins by talking about a famous French author by the name of Marcel Proust who wrote pages of memories that was triggered by the smell of Madeleines. The writings of Proust help describe how odors can be connected to very detailed long-term memories. The Proust effect, which is described as the recall of episodic memories after an odor stimuli has been greatly studied and researchers have hypothesized the cause of this phenomenon to be due to the location of the olfactory system being very close the brain. The author highlights new findings that show “spatiotemporal information is integrated in a brain region known as the anterior olfactory nucleus (AON), which is implicated in Alzheimer’s disease” (Sandoiu). A researcher by the name of Afif Aqrabawi conducted a study in which mice were subjected to a range of experiments and tests to examine the role of the anterior olfactory nucleus on memory. In the article it states that Aqrabawi’ s study led to the discovery of neural pathways between the hippocampus and the anterior olfactory nucleus. In the experiments, mice were presented with odors and Aqrabawi says that when the neural connection between the hippocampus and AON is intact, the mice preferred spending time smelling a new odor instead of a familiar one. With the neural pathway disrupted, mice preferred to smell the familiar odor as they thought it was a new odor. Aqrabawi explains how this observation helps to better understand the neural circuits that are responsible for episodic memory triggered by smell. The article also talks about how Alzheimer’s disease has shown early degradation of the anterior olfactory neuron and that the odor deficits that are experienced by people who suffer Alzheimer’s have difficulty remembering details about the odors they encountered. The neural pathway that was discovered in Aqrabawi’ s study may be a clue to better understand what the underlying causes of this are.

The research being done by Shanahan, and the study done by Aqrabawi that was described in Sandoiu’ s article, shows the deep connection of the olfactory system and memory. The experiments done in Shanahan’s lab show how even during sleep olfaction can be used as a tool to shape memory consolidation. The olfactory pathway is connected to the limbic system, which is involved in memory and emotion and during sleep, odorants can be presented to individuals without them being aware and awake. Even without participants being actively awake, it reinforces the encoding of memories. The discovery of new connections in Aqrabawi’ s study greatly helps get closer to explaining why odors are so involved with memory. Further research in the relationship between odor and memory can possibly reveal methods that can be used in learning. This research can possibly be used to answer questions regarding if odor can be used to help better encode information in a shorter span of time. How can olfaction help in neurodegenerative disease and maybe in cases of amnesia? While there are many studies focused on the relationship between smell and memory, there is a lot yet to be uncovered.

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Sandoiu, Ana. “Why Smells Bring Back Such Vivid Memories.” Medical News Today, MediLexicon International, 26 July 2018, www.medicalnewstoday.com/articles/322579.

Shanahan, Laura K., and Jay A. Gottfried. “Scents and Reminiscence: Olfactory Influences on Memory Consolidation in the Sleeping Human Brain.” Cognitive Neuroscience of Memory Consolidation, 2017, pp. 335–346., doi:10.1007/978-3-319-45066-7_20.