A report on Hippocampus and Episodic memory

Long-term memory is commonly labelled as explicit memory (declarative), as well as episodic memory, semantic memory, autobiographical memory, and implicit memory (procedural memory).

These are encoded by the hippocampus, entorhinal cortex, and perirhinal cortex, but consolidated and stored elsewhere.

Explicit memory can be divided into two categories: episodic memory, which stores specific personal experiences, and semantic memory, which stores factual information.

Although many psychologists believe that the entire brain is involved with memory, the hippocampus, and surrounding structures appear to be most important in declarative memory specifically.

Under declarative memory resides semantic and episodic memory.

The hippocampus is essential (for learning new information) to the consolidation of information from short-term to long-term memory, although it does not seem to store information itself.

Declarative (denotative) or explicit memory is conscious memory divided into semantic memory (facts) and episodic memory (events).

Medial temporal lobe structures that are critical for long-term memory include the hippocampus, along with the surrounding hippocampal region consisting of the perirhinal, parahippocampal, and entorhinal neocortical regions.

To a large degree, anterograde amnesia remains a mysterious ailment because the precise mechanism of storing memories is not yet well understood, although it is known that the regions of the brain involved are certain sites in the temporal cortex, especially in the hippocampus and nearby subcortical regions.

Furthermore, the data do not explain the dichotomy that exists in the MTL memory system between episodic memory and semantic memory (described below).

The second process is systems consolidation, occurring on a much larger scale in the brain, rendering hippocampus-dependent memories independent of the hippocampus over a period of weeks to years.

Multiple trace theory (MTT) builds on the distinction between semantic memory and episodic memory and addresses perceived shortcomings of the standard model with respect to the dependency of the hippocampus.

In addition, specific areas of the hippocampus (the CA1 region) are involved with memory.

Retrograde amnesia is inability to recall memories before onset of amnesia. One may be able to encode new memories after the incident. Retrograde is usually caused by head trauma or brain damage to parts of the brain besides the hippocampus. The hippocampus is responsible for encoding new memory. Episodic memory is more likely to be affected than semantic memory. The damage is usually caused by head trauma, cerebrovascular accident, stroke, tumor, hypoxia, encephalitis, or chronic alcoholism. People with retrograde amnesia are more likely to remember general knowledge rather than specifics. Recent memories are less likely to be recovered, but older memories will be easier to recall due to strengthening over time. Retrograde amnesia is usually temporary and can be treated by exposing them to memories from the loss. Another type of consolidation (process by which memories become stable in the brain) occurs over much longer periods of time/days, weeks, months and years and likely involves transfer of information from the hippocampus to more permanent storage site in the cortex. The operation of this longer-term consolidation process is seen in the retrograde amnesia of patients with hippocampal damage who can recall memories from childhood relatively normally, but are impaired when recalling experiences that occurred just a few years prior to the time they became amnesic. (Kirwan et al.,2008)In the case of LSJ, her case shows that retrograde amnesia can affect many different parts of knowledge. LSJ was not able to remember things from her child or adult life. She was not able to remember things that most people pick up in everyday life such as logos or the names of common songs.

The disease is known to target the hippocampus which is associated with memory, and this is responsible for the first symptoms of memory impairment.

Older memories of the person's life (episodic memory), facts learned (semantic memory), and implicit memory (the memory of the body on how to do things, such as using a fork to eat or how to drink from a glass) are affected to a lesser degree than new facts or memories.

Semantic memory is distinct from episodic memory, which is our memory of experiences and specific events that occur during our lives, from which we can recreate at any given point.

On the one hand, many researchers and clinicians believe that semantic memory is stored by the same brain systems involved in episodic memory, that is, the medial temporal lobes (MTL), including the hippocampal formation.

Autobiographical memory is a memory system consisting of episodes recollected from an individual's life, based on a combination of episodic (personal experiences and specific objects, people and events experienced at particular time and place) and semantic (general knowledge and facts about the world) memory.

Finally, the autobiographical memory differences may be attributed to a smaller posterior hippocampal volume in any individuals going through cumulative stress.