Memory and sleep are things that often go hand in hand when brought up in conversation, especially in academia. Beginning as early as pre-K and well into adulthood, memory loss is often attributed to sleep, or lack thereof. Because of this many studies have looked into this correlation and studied various aspects of memory, sleep, sleep stages, learning, and consolidation. The two presented papers that will be discussed today talk about all of these things. Susan J. Sara investigates the role of sleep in memory consolidation through personal work and the work of others to understand where, why, and how. Shanahan and Gottfried present research into a more specific experimental aspect of learning, sleep and memory, through olfactory influences and memory consolidation during slow-wave sleep (SWS).
Susan J. Sara presents background and current research into the role of sleep for memory consolidation. In this article, discussion of the two sleep states (REM and SWS), memory processing, and the sequential hypothesis is discussed. In her discussion, she cites studies that have looked at the role of REM and SWS. It is recorded that REM sleep is more involved in the consolidation of procedural memory, such as knowing the motor skills of a task, while SWS is more involved in the consolidation of declarative memory, such as knowing what. Shanahan and Gottfried’s studies definitely support the latter, and Sara’s paper expands on this topic. In the section SWS and memory, Sara cites Buzsaki’s (1989) “two stage” hypothesis for memory formation. This hypothesis suggests that the neuronal discharges occurring during wakefulness and exploratory activity during high hippocampus activity should be replayed in a “time-compressed manner”. This time-compressed replay presents specific cues associated with learning during SWS and shows facilitation of memory performance when waking. An olfactory modality memory study, similar to Shanahan et al, with rodents was done using rodents that provided strong evidence of cue-induced bias determining specific neuronal ensembles replayed during sleep. The sequential hypothesis, proposed by Giuditta, also suggested that each stage of sleep played distinct but complementing roles in memory processing. The study done in relation to this hypothesis found evidence of “tagging” for “relevant” and “irrelevant” information memory integration. This has been widely accepted after further study with strong supporting evidence of memory traces relocating to specific cerebral sites. SWS shows to be involved in initial informational processing while REM acts as a subsequent information consolidator.
Shanahan and Gottfried presented research and origins into the correlation between olfactory influences and memory consolidation. Their research targeted smells that they introduced to subjects during memory tasks and reintroduced during SWS and upon awakening before performing the task again. The olfactory tasks were centered around the ability of the odors presented to reactivate declarative memory consolidation. These tasks were in line with the hypothesis and showed a substantial positive effect on memory consolidation in subjects who underwent the same odor conditions pre and post (SWS) sleeping. TMR studies that looked outside of the realm of declarative memory consolidation found that subjects in the target odor condition generated more creative solutions when woken up again. In this study however, lack of EEG monitoring limits the application of this study but evidence still remains. Despite this, additional studies regarding reactivation outside of declarative memory was studied. Hauner et al looked at how the use of olfactory TMR could modulate emotional memory consolidation (also during SWS). What they found is that the fear response hypothesized to be reactivated upon the contextual odor delivery after waking actually declined. From this, strong suggestions that odors can promote fear extinction during sleep pose the ability to be studied or later applied to anxiety disorder management/therapy. The work presented by Shanahan and Gottfried shows strong support for the possibility to use odors as memory consolidation tools, enhancement tools, and even fear quelling. It is reported in the paper that application to anxiety disorders shows promise as well.
It is useful to understand these papers in a complementary context because Sara provides an in-depth background of the mechanisms of REM and SWS sleep stages that help aid in the understanding of Shanahan et al study. Additionally, Sara references several pieces of research that have allowed for the building of knowledge into this specific area and allows for acceptance of theories that allow us to continue to question others and reveal new information. Shanahan and Gottfried also highlighted the history of olfactory influences into memory consolidation and were able to apply it to modern day issues for possible treatments. The conclusion of Sara’s paper calls for action into continuing study into the neurobiology of memory consolidation. The ever growing state of awareness into non-neurotypical patients poses the heightened need to provide spaces beyond acceptance. Change, understanding, comfortability, and an ultimate solution to these problems requires studies such as the experimental approach that Shanahan et al took. This approach takes the history of scientific knowledge and builds on that for assurity and the goal of finding a why and how to address deficits in these areas.
Sara, S. J. (2017). Sleep to remember. The Journal of Neuroscience, 37(3), 457-463.
doi:10.1523/jneurosci.0297-16.2017
Shanahan, L. K., & Gottfried, J. A. (2017). Scents and reminiscence: Olfactory influences on
memory consolidation in the sleeping human brain. Cognitive Neuroscience of Memory
Consolidation, 335-346. doi:10.1007/978-3-319-45066-7_20
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