Hippocampal memory encoding and retrieval: Difference between revisions

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The [[hippocampus]] participates in the encoding and retrieval of memories. <ref name=a /> The hippocampus is located in the medial temporal lobe (subcortical), and is an infolding of the medial temporal cortex. <ref name=a>Gazzaniga, Michael S., Richard B. Ivry, and G. R. Mangun. "Chapter 9: Memory." Cognitive Neuroscience: The Biology of the Mind. 4th ed. New York: W. W. Norton, 2014. 378-423. Print.</ref> The hippocampus plays an important role in the transfer of information from [[short-term memory]] to [[long-term memory]] during encoding and retrieval stages. These stages need not occur successively, but are, as studies indicate, broadly divided in the neuronal mechanisms they require or even in the hippocampal areas they activate. According to Gazzaniga, “encoding is the processing of incoming information that creates memory traces to be stored.”<ref name=a /> There are two steps to encoding: acquisition and consolidation. During acquisition, stimuli are committed to short term memory.<ref name=a /> Consolidation is where the hippocampus along with other cortical structures stabilize an object within long term memory, a process strengthening over time and one for which a number of theories have arisen to explain. <ref name=a /> After encoding, the hippocampus is capable of going through the retrieval process. The retrieval process consists of accessing stored information; this allows learned behaviors to experience conscious depiction and execution.<ref name=a /> Encoding and retrieval are both affected by [[neurodegenerative]] and [[anxiety disorders]] and [[epilepsy]].

==Introduction==

The [[hippocampus]] participates in the encoding and retrieval of memories. <ref name=a /> The hippocampus is located in the medial temporal lobe (subcortical), and is an infolding of the medial temporal cortex. <ref name=a>Gazzaniga, Michael S., Richard B. Ivry, and G. R. Mangun. "Chapter 9: Memory." Cognitive Neuroscience: The Biology of the Mind. 4th ed. New York: W. W. Norton, 2014. 378-423. Print.</ref> The hippocampus plays an important role in the transfer of information from [[short-term memory]] to [[long-term memory]] during encoding and retrieval stages. These stages need not occur successively, but are, as studies indicate, broadly divided in the neuronal mechanisms they require or even in the hippocampal areas they activate. According to Gazzaniga, “encoding is the processing of incoming information that creates memory traces to be stored.”<ref name=a /> There are two steps to encoding: acquisition and consolidation. During acquisition, stimuli are committed to short term memory.<ref name=a /> Consolidation is where the hippocampus along with other cortical structures stabilize an object within long term memory, a process strengthening over time and one for which a number of theories have arisen to explain. <ref name=a /> After encoding, the hippocampus is capable of going through the retrieval process. The retrieval process consists of accessing stored information; this allows learned behaviors to experience conscious depiction and execution.<ref name=a /> Encoding and retrieval are both affected by [[neurodegenerative]] and [[anxiety disorders]] and [[epilepsy]].

==Theories and Reasoning==

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The reconsolidation hypothesis has lingered since the 1960s; however, a 2000 study, entitled “Fear memories require protein synthesis in the amygdala for reconsolidation after retrieval”, examining fear conditioning in rats, has provided evidence in its favor.<ref name=e>Nader, Karim, Glenn E. Schafe, and Joseph E. Le Doux. 'Fear Memories Require Protein Synthesis In The Amygdala For Reconsolidation After Retrieval'. Nature 406.6797 (2000): 722-726. doi:10.1038/35021052</ref> After receiving post-retrieval an intra-amygdalar infusion of a known amnesic agent, anisomycin, rats failed to recall a rapidly learned fear memory.<ref name=e /> Hippocampal lesions formed post-retrieval affected the rats' fear conditioning in a similar manner.<ref name=e />

The reconsolidation hypothesis does not suppose that subsequent and precedent consolidation phases are necessarily identical in duration or in the neural mechanisms involved. Nevertheless, the commonality that exists in every consolidation phase is a short-lived destabilization of a memory object and a susceptibility for said object to react to amnesic agents -- principallyagents—principally protein synthesis inhibitors.<ref name=d /> Morris and colleagues’ experiment indicates that the reconsolidation hypothesis could apply to particular memory types such as allocentric spatial memory, which is either acquired slowly or rapidly. As implied by the authors, however, such an application is feasible only in the case of rapidly acquired spatial memory, the degree to which is influenced by how thoroughly a spatial object is trained.<ref name=d />

==Hippocampal Disorders that affect Encoding and Retrieval==

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===Psychiatric Disorders===

Individuals who develop hippocampal lesions often fare poorly on measures of verbal declarative memory. Tests involving the recall of paragraphs or strings of words, as cited by Bremner and colleagues, illustrate a degree of dysfunction among lesion patients proportionate to the percentage of hippocampal volume and the amount of cells lost.<ref name=f>Bremner, J., Vythilingam, M., Vermetten, E., Southwick, S., MaGlashan, T., Nazeer, A., Khan, S., Vaccarino, V., Soufer, R., Garg, P., Chin, K., Staib, L., Duncan, J., Charney, D. (2003). MRI and PET study of deficits in hippocampal structure and function in women with childhood sexual abuse and posttraumatic stress disorder. The American Journal of Psychiatry, 160, 924-932</ref>

As precursors toward later studies that would showcase the effect of [[Post-Traumatic Stress Disorder]] (PTSD) on the human hippocampus, animal studies have broadly demonstrated a susceptibility of the mammalian hippocampus to stressors. In particular, stressed animals develop functional deficits in memory, changes in hippocampal form, and an impairment in neurogenesis, or the ability to produce new neurons.<ref name=f />

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===Methods===

In an experiment performed by Zeineh and colleagues, ten subjects were scanned by fMRI while engaged in a face-name associative task that linked a sequence of faces unknown to the participants with the names of the individuals to whom they belonged.<ref name=j>Zeineh, M. (2003). Dynamics of the Hippocampus During Encoding and Retrieval of Face-Name Pairs. Science,299(5606), 577-580. doi:10.1126/science.1077775</ref> The hippocampus is known to play a role in the encoding of memory that associates between a face and a name. The experiment began by dividing encoding blocks, in which the participants viewed and attempted to memorize the faces paired with the names, from retrieval blocks, in which the participants were shown only the faces and asked to match them with their names. This process was completed four times. <ref name=j /> Rote rehearsal was discouraged by a distractive task administered between encoding and recall blocks.<ref name=j />

===Results===

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[[Category:Health care]]

[[Category:Health sciences]]