PTSD and Memory Recall in Mice and Veterans

        We have all been transported to a different time or had a feeling of nostalgia after smelling a familiar scent. This experience is known as the Proust Phenomenon, and the memories we experience could be cheerful, stressful, or even traumatic. Odor is hypothesized to trigger a response within the hippocampus for recent memories and rely more heavily on the prefrontal cortex for older ones. This hypothesis is backed up by the research conducted by Dr. Stephanie L. Grella in which she studies fear memory consolidation within mice (1). In addition to smelling a familiar scent, tasting a flavor that reminds you of a memory is a component of odor. In an article posted by Harvard University, Dr. Venkatesh Murthy states, “[food molecules] make their way back retro-nasally to your nasal epithelium… all of what you consider flavor is smell” (Walsh). Additionally, odor travels directly to the limbic system and to the hippocampus and amygdala which are associated with emotion and memory. Thus, the relationship between odor and memory can probably be attributed to the relations between the limbic system. 

        Grella focused on fear memory consolidation in her research and attempted to connect how the hippocampus and the prefrontal cortex function to trigger traumatic memories. Through the results, she concludes that during fear conditioning, odor “biased the memory system away from the PFC and toward the HPC” indicating that memory retrieval relies heavily on the hippocampus (7). The exposure to a specific scent caused the mice to remember the traumatic event they had endured in the past. Thus, the Proust Phenomenon was observed in the mice and indicates the strong relationship between odor and memory in the brain. 

        Moreover, a similar study by Dr. Cortese focuses on PTSD in veterans rather than focusing on mice. This study explores how odor plays a role in the pathophysiology of PTSD. PTSD is defined as “a condition characterized by intrusive thoughts or memories, avoidance of stimuli and contextual reminders, as well as increased startle, hypervigilance, and focused attention to potential threat cues” (Cortese 2). Cortese states that many veterans report that odor plays a significant role in triggering their PTSD. Their results however indicate that the olfactory system and the brain do not trigger a PTSD response within veterans every time they smell a specific scent. Thus, it is probable that within the human brain, the olfactory system is highly sophisticated and is not as sensitive to the triggering scent. 

       The two different studies mentioned represent PTSD within mice and humans. In the mice, it was observed that the HPC plays a significant role in triggering a fear response within the mice. The same can be said for the study within humans. However, as seen in the veteran study, the human brain does not react

to a triggering scent the same way each time. This points to the sophistication of the olfactory system. Both studies work together to help researchers understand the Proust Phenomenon at a biological and psychological level. 

References

Cortese, Bernadette M et al. “Differential odor sensitivity in PTSD: Implications for

treatment and future research.” Journal of affective disorders vol. 179 (2015): 23-30. doi:10.1016/j.jad.2015.03.026  

Grella, Stephanie L. “Odor Modulates the Temporal Dynamics of Fear Memory Consolidation.” Http://Learnmem.cshlp.org/Content/27/4/150.Full, Cold Spring Harbor Laboratory Press, 2020, http://learnmem.cshlp.org/content/27/4/150. 

 

Walsh, Colleen. “How Scent, Emotion, and Memory Are Intertwined - and Exploited.” Harvard Gazette, Harvard Gazette, 27 Feb. 2020, https://news.harvard.edu/gazette/story/2020/02/how-scent-emotion-and-memory-are-intertwined-and-exploited/.