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Reference: Frankland PW, Josselyn SA, Köhler S. The neurobiological foundation of memory retrieval. Nat Neurosci. 2019 Oct;22(10):1576-1585. doi: 10.1038/s41593-019-0493-1. Epub 2019 Sep 24. PMID: 31551594; PMCID: PMC6903648.

Memory retrieval Introduction

The process happens as a result of interaction between sensory cues and the memory traces stored in the human brain. Memory retrieval is dependent on the cues therefore, a specific memory can be retrieved with some cues and not by others as was shown by the experiment of Tulving and Pearlstone [1]. Various studies have been done that shows the activation of the neural activities accounts for the memory retrieval that brain generated when a specific event took place. However, it is not necessary to have photogenic memory of the events whose retrieval happens. They are not completely similar to the actual events. Mind can leap in the future and can go back in the past because of the information stored in it and having access for that. The memory is divided into three phases namely encoding of the information or when the event is happening, the ongoing phase, and finally the retrieval part. It is said that this behaviour of the mind of retrieving memories supported by hippocampus.

Types of memory retrieval

Broadly speaking, there are three different types of memory retrieval namely, free recall, serial recall, and cued recall. As the name suggest, free recall does not has any specific order in recalling the memories and it happens randomly. The recalling in this type further takes place in three different ways that is through primacy effect, recency effect, and finally the cognitive effect based on the position of the recalls [2]. To its contrary, serial recall retrieve the memory in set order in which the events occurred or it recall the events in chronological order. One memory acts as cue for another memory and so on the retrieval process takes place. However, as the number of memories increase in the list, recency and primacy events can exist in the serial recall type of memory retrieval. Moreover, in cued recall, as the name suggests, the retrieval process takes place due to the existence of specific guides and cues. These memories are generally not seen in free recall because only after using several cues, recalling happens [2]. Furthermore, retrieval process is also affected by several factors such as environment where memory was encoded, gender, the amount of attention paid to an event when it was occurring, and physical activity where the retrieval increases with healthy eating habits.

Brain in memory retrieval

The process of recalling and recognition of the memory involves several different parts of the brain. Studies until now have identified six such parts namely prefrontal cortex, hippocampus, anterior cortex, posterior midline area, parietal cortex, and cerebellum. Encoding of the new memories takes place in the hippocampus while cerebellum processes the procedural memory [3]. Hippocampus also projects the memory information to another region of the brain that is cortical region that helps in connecting the memories to other related memories. Based on the intensity of the emotional response against an event, amygdala determines whether the event will be stored or not as memory. This cognitive process is biologically dependent process. It is believed by the scientists that complete brain has some role to play in the memory storage and retrieval process. Neurotransmitters are also important in the development of the memory but their role is not yet vividly known. However, according to the Arousal theory, the release of these neurotransmitters define how weak or strong a memory would be [3]. This theory also defines why the emotional events are more prominent in the memory compared to the memory of the non-emotional events.

Retrieval failure

It is mostly seen that the memory is stored in the brain but it is difficult to recall it. It is commonly called is retrieval failure. This phenomena generally occurs because the brain do not receive enough sensory cues that will trigger the recall process. It is also likely that the encoding of the information in the brain did not happen and thus recalling does not happen. For instance, one can draw a penny based on the memory but not in detail because the detail of the penny was never focused upon and thus it is not stored in the memory in the first place [4]. This absence of the information is underlying reason for not been able to draw the detailed photo of a penny even though its shape and colour can be drawn easily. Failure also happens when the memory cannot be accessed probably because the information for that memory is stored in long-term memory [6]. Therefore, two factors responsible for the failure in recalling of the memory are lack of appropriate cues and encoding failure. In the former, even if the memory is stored, it cannot be retrieved completely or partially. The intensity of the memory also decreases over the time even if the memory is associated with strong triggering cues. Flashbulb memories are strong and can be remembered for longer times. For instance, remembering the spatial location when a brutal event took place cannot be forgotten for longer times [5]. This is because such events can have strong emotional connection with some people. However, these memories fade away over the time. Tip of the tongue is associated with this failure in the recalling and recognition of the memory [7]. Even though the memory is at the tip of the tongue but due to the lack of cues and because appropriate encoding did not happen, the memory was not retrieved even though it is stored in some part of the brain.

Conclusion

It can be inferred that different parts of the brain play different role in the retrieval of the memory. This retrieval process of the memory is possible because some cues and sensory events are present to trigger the recalling of the events. Retrieval process is linked to the strength of the emotions attached with the memory. If the memory is associated with strong emotions, its retrieval is easy while it may or may not be retrieved if the cues are weak. However, enough studies have not yet happened but it is clear that the cognitive activity of the brain helps in memory retrieval.

References

1.	Ritvo, V.J., Turk-Browne, N.B. and Norman, K.A., 2019. Nonmonotonic plasticity: how memory retrieval drives learning. Trends in cognitive sciences, 23(9), pp.726-742. 2.	Gagnon, S.A. and Wagner, A.D., 2016. Acute stress and episodic memory retrieval: neurobiological mechanisms and behavioral consequences. Annals of the New York Academy of Sciences, 1369(1), pp.55-75. 3.	DeNardo, L.A., Liu, C.D., Allen, W.E., Adams, E.L., Friedmann, D., Fu, L., Guenthner, C.J., Tessier-Lavigne, M. and Luo, L., 2019. Temporal evolution of cortical ensembles promoting remote memory retrieval. Nature neuroscience, 22(3), pp.460-469. 4.	Xu, C., Krabbe, S., Gründemann, J., Botta, P., Fadok, J.P., Osakada, F., Saur, D., Grewe, B.F., Schnitzer, M.J., Callaway, E.M. and Lüthi, A., 2016. Distinct hippocampal pathways mediate dissociable roles of context in memory retrieval. Cell, 167(4), pp.961-972. 5.	Bowen, H.J. and Kensinger, E.A., 2017. Recapitulation of emotional source context during memory retrieval. Cortex, 91, pp.142-156. 6.	Kerrén, C., Linde-Domingo, J., Hanslmayr, S. and Wimber, M., 2018. An optimal oscillatory phase for pattern reactivation during memory retrieval. Current Biology, 28(21), pp.3383-3392. 7.	Scholz, A., Mehlhorn, K. and Krems, J.F., 2016. Listen up, eye movements play a role in verbal memory retrieval. Psychological research, 80(1), pp.149-158.