With the ongoing SARS-COV2 (COVID-19) pandemic, it is not uncommon for individuals to be hyper aware of the associated symptoms. For some people, the onset of COVID-19 begins with the loss of smell and taste which can be both terrifying and uncomfortable. This loss of smell, also known as anosmia or more specifically COVID-19 anosmia, can present both short and long term effects for those who suffer from it. Fortunately, for many individuals, COVID-19 anosmia will be short term. However, for those who suffer the long term effects of this symptom, there could be a lasting neurological effect as well: memory consolidation complication.
Smell has an effect on our ability to consolidate memory. In a 2017 study by Dr. Laura Shanahan et.al titled “Scents and Reminiscence: Olfactory Influences on Memory Consolidation in the Sleeping Human Brain,” the researchers reviewed past literature done on comparing the effects of odors and memory consolidation. Dr. Shanahan focuses on a 2007 study by Dr. Rasch et.al, where the researchers used phenylethyl alcohol which produced a rose smelling odor to determine the effects of odor and memory consolidation. In the study the participants were asked to memorize the location of multiple card pairs while simultaneously being introduced to the phenylethyl alcohol odor prior to sleep. Once asleep, the odor was continuously presented in a 30 second on and off pattern. Once awake, the participants were tasked with remembering the location of the card pairs. The results of the study indicated that participants remembered the card pair locations better when introduced to the phenylethyl alcohol prior to slow wave sleep. This indicated that odor did have an effect on the ability to consolidate memory. The principle necessity of this study required participants to have a sense of smell, but what are the implications on memory for those who have lost their sense of smell?
Anosmia is an early indicator of COVID-19 disease according to a 2020 study “Anosmia in COVID-19: Mechanisms and Significance” by Dr. Albert Han. One of the key areas which connects memory consolidation to olfactory sensing is an area in the brain known as the anterior olfactory nucleus (AON). According to Dr. Han “Recent studies have shown that the AON utilizes input from the hippocampus for storage of olfactory memory representations” (Han 424). Dr. Han references a study from Afif Aqrabawi from the University of Toronto titled “Scientists Uncover New Connection Between Smell and Memory,” which went into more depth about the mechanism and purpose of the AON. Much like COVID-19, anosmia is an early indicator in Alzheimer’s disease. The AON is important in the pathology of Alzheimer's Disease which is commonly associated by the general population with memory loss. According to this study, the AON begins to degrade early on in the pathology of Alzheimer's which is evident by the associated early-onset anosmia. In the study, Afif Aqrabawi used mice with a severed AON to Hippocampus connection in addition to the control which were mice with a normal connection. The resulting effects led to mice with an intact connection preferring odors they had previously smelled. Those mice with a severed connection gravitated toward new smells because they were unable to make the connection with the previously presented odor and past experiences. This led Afif Aqrabawi to conclude that the AON is responsible for pairing the location and time of a stimulus, with the stimulus itself.
The link between Alzheimer’s, COVID-19, and Dr. Shanahan’s paper is the AON. Because the AON is associated with pairing a stimulus and location/time, damage to the AON will greatly disadvantage memory consolidation to those affected by it. Because the overall neurological damage caused by COVID-19 is still under review, the possibility of AON damage might hold the key for understanding the long term memory implications of COVID-19. Reverting back to the study by Dr. Rasch et.al, the ability to consolidate memory better after smelling the phenylethyl alcohol only worked when the individual could smell. The potential pathology of COVID-19 anosmia presents the possibility that those who suffer its effects will not be able to consolidate memory as well as their normosmia (normal smelling ability) counterparts. This ultimately puts these individuals at a disadvantage for potential memory consolidation in addition to the already unpleasant effects anosmia presents.
References
Aqrabawi, Afif. “Scientists Uncover New Connection between Smell and Memory.” ScienceDaily, ScienceDaily, 23 July 2018, www.sciencedaily.com/releases/2018/07/180723155726.htm.
Han, Albert Y, et al. “Anosmia in COVID-19: Mechanisms and Significance.” Chemical Senses, Oxford University Press, 17 June 2020, www.ncbi.nlm.nih.gov/pmc/articles/PMC7449368/.
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.
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