The evolutionary sense of olfaction and its role in strengthening fear memories

            Previous research on olfaction has established it as an ancient evolutionary sense but has still yet to determine the extent to which it can influence human behavior. In the article “An Evolutionarily Threat-Relevant Odor Strengthens Human Fear Memory”, researchers Taylor et al. investigated whether threat-related predator odors would contextually enhance the formation of human fear memory associations. Notably, the authors made a distinction between odor acting as a powerful cue for triggering recall of fear memories vs. the ability of odor to act as contextual modulators of fear memory formation. Another key difference was that many other studies exposed the experimental animals to odors at the same time as fear memory formation which establishes odors as direct cues for the learned associations. However, in this study the researchers sought to set odor as a simple background context to investigate how odors may actually affect fear learning. In the study, Taylor et al. found that participants who learned to associate the visual stimuli with the electric shock given the predator odor context eventually showed stronger fear responses to the same visual stimuli compared to the participants who learned these associations in an aversiveness-matched control odor context. Even after extinction training, this effect generalized to testing in other odor contexts. The authors also noted a separate secondary experiment that indicated a “​​possible biological mechanism for this effect may be increased cortisol levels in a predator odor context” (Taylor et al., 2020). This suggests that the innate olfactory processes do play an important role in human fear learning. Applications of the research can be extended to partly explaining the maladaptive persistence of human fear memory, like for example, in post-traumatic stress disorders.

            This contemporary article’s findings relate to another research study on the same topic presented in class. In the article “Odor modulates the temporal dynamics of fear memory consolidation”, researchers Grella et al., sought to determine how odor is a particularly evocative cue for intense remote memory recall. The authors also considered instances such as post-traumatic stress disorders where there is intense remote memory recall which can occur even years after trauma. Here, the authors hypothesized that “odor may shift the organization of salient or fearful memories such that when paired with an odor at the time of encoding, they are delayed in the de-contextualization process that occurs across time, and retrieval may still rely on the HPC, where memories are imbued with contextually rich information, even at remote time points” (Grella et al., 2021). Their results demonstrated that odor did indeed shift the organization of fear memories at the systems level.

References

Grella, Stephanie L., et al. “Odor Modulates the Temporal Dynamics of Fear Memory Consolidation.”      

Learning & Memory, Cold Spring Harbor Lab, 1 Jan. 1970, http://learnmem.cshlp.org/content/27/4/150.full. 

Taylor, Jessica E., et al. “An Evolutionarily Threat-Relevant Odor Strengthens Human Fear Memory.” Frontiers, Frontiers, 1 Jan. 1AD, https://www.frontiersin.org/articles/10.3389/fnins.2020.00255/full.