Between-systems memory interference model: Difference between revisions

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== History ==

The hippocampus (HPC) plays an important role in memory processes/functioning. It is a cortical structure in the anterior medial temporal lobe which is involved in the consolidation of short-term and long-term memories, specifically for memories of spatial navigation<ref name="post">{{cite book|last=Kolb|first=Bryan|title=Fundamentals of Human Neuropsychology|year=2009|publisher=Worth Publishers|___location=New York: NY|edition=6th|coauthorsauthor2=Whishaw, Ian Q.}}</ref> However there are other cortical structures involved in memories which are referred to as non-HPC memory systems. The relationship between the HPC and non-HPC systems is often studied using [[fear conditioning]], which is a form of learning where a noxious stimulus, such as an odour or shock, creates an emotional response of fear. The [[amygdala]] is often associated with these responses in fear conditioning in which conditioned stimuli can evoke emotional memories. Indirect measures of fear conditioning, such as freezing time, have been used to infer the functional levels of spatial and learning memory <ref>{{cite journal|last=Sparks|first=F.T.|author2=Lehmann, H.|author3=Sutherland, R.J.|title=Between-systems memory interference during retrieval|journal=European Journal of Neuroscience|year=2011|volume=34|pages=780–786|doi=10.1111/j.1460-9568.2011.07796.x|issue=5}}</ref>

Researchers began believing other cortical structures, aside from the HPC, were involved in memory of contextual fear conditioning, because when the HPC was extensively damaged before fear conditioning, there was only a small effect on levels of behavioural memory assessments.<ref name="test">{{cite journal|last=Lehmann|first=H|author2=Sparks, F.T.|author3=Spanswick, S.C.|author4=Hadikin, C.|author5=McDonald, R.J.|author6=Sutherland, R.J.|title=Making context memories independent of the hippocampus|journal=Cold Spring Harbor Laboratory Press|year=2009|volume=16|pages=417–420}}</ref> It was deduced that other non-HPC memory systems must be involved in encoding, storing and retrieving memories during contextual fear conditioning, and that normally the HPC interferes with these processes.<ref name="best">{{cite journal|last=Sutherland|first=R.J.|author2=Lehmann, H.|author3=Spanswick, S.C.|author4=Sparks, F.T.|author5=Melvin, N.R.|title=Growth points in research on memory and hippocampus|journal=Canadian Journal of Experimental Psychology|year=2006|volume=60|pages=166–174|doi=10.1037/cjep20060016|issue=2}}</ref> The mechanism of this [[interference theory|interference]] is not entirely known, however studies have alluded to the ___location of this interference. Researchers have found that during fear conditioning the HPC competes with the non-HPC memory systems in the basolateral region of the amygdala.<ref>{{cite journal|last=Biedenkapp|first=J.C.|coauthorsauthor2=Rudy, J.W.|title=Hippocampal and extra-hippocampal systems compete for control of contextual fear: Role of ventral subiculum and amygdala|journal=Learning & Memory|year=2009|volume=16|pages=38–45|doi=10.1101/lm.1099109}}</ref> Injections of a dopamine D1 agonist SKF82958 into this area of the amygdala before a conditioning session were correlated with a decrease in the interference by the HPC, allowing non-HPC systems to form memories of the fear conditioning. Therefore the increased dopamine to this area, inhibits amygdala functioning which includes the HPC interfering with memory encoding in non-HPC systems.

In studies of contextual fear conditioning, there are many views describing the interaction between HPC and non-HPC systems, or the transition of memories from being hippocampus dependent to independent. The HPC and non-HPC systems may acquire the same memories but if the HPC is intact, the non-HPC systems cannot independently form or retrieve these context memories.<ref name="test" /><ref name="best" /> Therefore the non-HPC systems appear to act like a back-up system for memories, that are only used when the main system, the HPC, is dysfunctional or absent. On the other hand, the HPC and non-HPC systems also have different functions. For example, the hippocampus is known to be important for context discrimination, while non-hippocampal systems have not shown evidence for this specific function <ref name="test" />

One view for the transfer of memories from HPC-dependent to independent is that the strength of memories changes across the HPC and non-HPC systems, with damage to the HPC. In a study by Lehmann and colleagues (2009)<ref name="test" /> adult male rats were put through contextual fear conditioning using feet shocks. If there was HPC damage and the rats experienced 11 sessions worth of shocks in one session, retrograde amnesia resulted. However if there was damage in the HPC and shocks were applied over many conditioning sessions, then the memory for the contextual fear conditioning was not affected. So within the numerous conditioning sessions, the memory for contextual fear conditioning may have been formed by the non-HPC memory systems. Specifically memory representations in the non-HPC systems may be strengthened and eventually become independent of the HPC, which normally overshadows/interferes with the non-HPC systems in forming representations of memories in contextual fear conditioning.<ref name="best" /> Conversely another view is that memories become independent of the HPC over time due to a reorganization of stored memories.<ref name="test" /><ref>{{cite journal|last=Squires|first=L.R.|coauthorsauthor2=Bayley, P.J.|title=The neuroscience of remote memory|journal=Current Opinion in Neurobiology|year=2007|volume=17|pages=185–196|doi=10.1016/j.conb.2007.02.006|issue=2}}</ref> Alternatively others believe memories change characteristics to become independent of the HPC, specifically in becoming less precise, more general and context free memories in non-HPC systems, assuming that the HPC is required for precise, detailed, contextual memories.<ref>{{cite journal|last=Moscovitch|first=M|author2=Nadel, I.|author3=Winocur, G.|author4=Gilboa, A.|author5=Rosenbaum, R.S|title=The cognitive neuroscience of remote episodic, semantic and spatial memory|journal=Current Opinion in Neurobiology|year=2006|volume=5|pages=179–190|doi=10.1016/j.conb.2006.03.013|issue=2}}</ref>

== Procedure ==