Taking a Look at Memory Consolidation

According to philosopher-psychologist William James, memory is a generalized concept that encompasses the long term and short term memory. Kendra Cherry, psychologist expert, defines long term memory as “storage of information over an extended period.” (Cherry n.d.) An individual’s long term memory is structured by a semi-permanent chemical and the anatomical hippocampus. The hippocampus is in the center of both hemispheres of the brain and works in accordance with the amygdala to allow information to be imported to form memories. In relation to her research of the long term memory, Cherry also provided information on the characterization of the short memory which is described as, the “primary or active memory” that presently takes in information. (Cherry n.d.) The thalamus is a large portion of a dual lobed mass of matter that is located under the cerebral cortex.

1 Background The hypothesis that remembering should be viewed as reconstructive originates from an important book by Sir Frederic Barlett (1932). Barlett compared the two forms of memory – reproductive (remembering a phone number) and reconstructive (remembering sixth grade) and declared that the second was a more standard use of memory outside laboratory and educational circumstances. He argued that

* Consolidation- hypothetical process involving gradual conversion of information into memory codes stored in long term memory.

Among these different processes are encoding, storage, consolidation, and retrieval. This study hypothesized that the hippocampus plays a different role in each of these. The method of this study is especially unique because it used temporary chemical inactivation of the hippocampus, which had not been done before. This temporary inactivation is unique because it lets the researchers selectively assess the role of the hippocampus during each of the processes discussed above. To test encoding, the inactivation occurred during learning of a maze task; to test retrieval, inactivation occurred during a retention task. Results indicate the temporary inactivation of the hippocampus impairs both encoding and retrieval. To test long-term consolidation, rats were trained and then separate groups received hippocampal treatment for different amounts of time between one and five days. Results showed that temporary inactivation during this time period disrupts memory for the already learned task. This study partially supports the result of the study by Eldridge et al. (2000) in that they both show the hippocampus is necessary for memory retrieval. However, it does not address the retrieval of different types of memory. This study also supports the idea from Wang et al. (2012) that the hippocampus may be involved in consolidation and storage of new memories but not necessarily of older

Additionally, to further support these theories, researchers tend to conduct studies on the famous patient case, HM, to propose the consolidation deficit theory, in which those with amnesia cannot turn short-term memories into long-term memories (Dewar et al., 2010). However, researchers Dewar, Della Sala, Beschin, and Cowan (2010), mentioned that HM’s case does not fully explain why a patient with anterograde amnesia has the ability to get better at cognitive tasks despite being unable to recall having performed those tasks at a previous time. On the same hand, Duff, Wszalek, Tranel, and Cohen (2008) mentioned that most individuals with anterograde amnesia experience heightened intelligence, attention, skill, and reasoning levels (procedural memory).

There is extensive evidence to prove that the hippocampus plays a vital role in memory retrieval. However the extent to what type of memories the hippocampus supports and the process in which retrieval occurs is an ongoing debate. The two theories that are dominant in this debate are the Standard Model of Systems Consolidation (SMSC) and the Multiple Trace Theory (MTT). This paper will provide a review on the evidence supporting these two composing theories, the research providing evidence against the models, and finally their limitations. Additionally, a novel theory coined the Competitive Trace Theory (CTT) will be reviewed in order to conclude whether or not this model can provide a more holistic and accurate representation of the role of the hippocampus in memory retrieval while simultaneously providing explanations for flaws in previously proposed models.

Much psychological research suggests that new memories require time to stabilize and transfer to long-term memory and that these newly acquired memories are disposed to to interference by competing stimuli. Memory consolidation is the processes involved in the stabilization of a long-term memory after it’s initial acquisition (Dudai, 2004). Consolidation is described by two distinct theories: synaptic consolidation, which transpires in the first few hours after learning and systems learning where memories are stabilized over a period of weeks to years (Dudai, 2004).

When forgotten and then remembered, the memory requires some form of restabilization such that the new information can re-incorporate itself with existing memory. Processual memory can be used in this context as well as when given new information or experience, a person’s association with an existing memory can change. No two memories are the same, which is why even the recirculation of memory can become corrupt over time and differ from the truth in relation to a process also known as “Rememory” as seen in Toni Morrison’s Beloved. The act of memory preservation is impossible as over enough time the memory will be muddled and the true context of the event will be forgotten. It is a process that we are unaware of until explicitly focused on because when people remember something that was once forgotten and the original memory is re-written it consolidates the image of that memory as the original. For example, if someone was remembering himself or herself as the star of a child play it could be a reformatted version of a memory of the play that was less than stellar. The idea of memory consolidation is to form coherent memory that people convince themselves to be true even if not recognized as the whole truth by reconstructing past

The retrieval of a memory can initiate processes in our brain that actively consolidate and strengthen the memory trace, a process known as memory reconsolidation. Memories retrieved are thought to increase their stability once they undergo the process of consolidation. Retrieval of a memory trace may cause another liable phase to require more processing to keep the memory stable after retrieval; the brain systemically acquires cellular mechanisms to initiate a new round of protein synthesis that saves the trace from degradation. (Rudy CITE) There has been recent issues concerning the relationship between post-traumatic stress disorder and reconsolidation of fear memories brought about by individuals who experience the disorder.

To learn from stressful events, memories of these events must be consolidated into long-term memory in case a similar situation occurs in the future. In the normal process of consolidating a memory, three different processes take place: synaptic long-term potentiation or LTP, systems consolidation, and reconsolidation (Depperman et al., 2014). LTP is a mechanism of neuroplasticity that increases the strength of certain synaptic connections through the stimulation of neurons involved in the connection. After an event happens, the new memory is transmitted to the hippocampus. Systems consolidation is the slow process by which memories are transferred from the hippocampus to the cortex such that memories are no longer hippocampus-dependent. Reconsolidation

The following experiment was preformed by Marieke Soeter and Merel Kindt. Their research tested if the disruption of reconsolidation of memories also lowers fear in an individual who has an ongoing fear of spiders in their everyday life. Studies over the past years have found that retrieving previously consolidated memories may signal a process known as reconsolidation (restabilization due to proteins). In the lab setting, a process known as Pavlovian fear conditioning can be used to train the mind to fear a stimulus. This conditioned fear can then easily be used to test the neurobiology of associative fear learning and memory. Fear conditioning is also a great method to be used in studying new treatments for anxiety disorders focused around

memory is not only prone to decay, but it is also vulnerable to the influence of post-event

After a new memory is learnt, it enters the process of encoding during which the memory is labile and capable of disruption until it becomes stabilised over a period of time (Nader & Einarsson, 2010; Nader et al, 2000). This process is called consolidation and originally consisted of the theory that once stabilised in the brain, it remains fixed (Suzuki et al, 2004). This theory has been rebutted by the acceptance of reconsolidation, a theory that imposes the ideology that when memories are retrieved, through similar experiences (Lee, 2009), they become labile until,

Scientists still to this day are studying whether long-term memories are fully lost. The purpose of human memory is to use past events to help guide their future actions, however; the human brain does not maintain perfect information of the past and is not reliable information. “The human brain can easily create false memories due to a misinterpretation of an event” (Carter 2009). “The chief explanations for forgetting include interference, retrieval failure, and constructive processes” (Loftus 2016). Memory interference happens when the remembering of specific material learned in the past blocks the memory formation of other new learned material. Human often experience having information “on the tip of their tongue” but are unable to recall

Retrieving memories, in contrast, increases hippocampal activity12 and often facilitates later recall13. Thus, hippocampal activity can be modulated according to task goals, though practice at suppressing retrieval is often necessary to achieve hippocampal reductions6. A key assumption of the present work is that this modulation does not target particular memories, which may be a person’s goal, but rather reflects a broadly targeted suppression (hereinafter, ‘systemic suppression’) of regional activity in the hippocampus that generally disrupts other memory functions supported by this region. For instance, beyond simply disrupting episodic retrieval, systemically suppressing hippocampal activity may also prevent freshly encoded stimulus input from generating new hippocampal traces