The ability to learn and recall something very well is an ability desired by many. While a pre-requisite of an effective brain is often attributed to this, not many know the part of the brain that is actually responsible for memory formation and the enhancement of learning.
Introducing the Hippocampus
For that very reason, let’s get to know a pair of structure in the brain called the Hippocampus. The word ‘Hippocampus’ is derived from the Greek word which translates to seahorse. This is because the shape of the Hippocampus mimics the shape of the animal. A bit of terminology lesson, a pair of the structure is called Hippocampus while a single structure of the pair is called a Hippocampi. The Hippocampus is located medial to the temporal lobe, deep in the center of the brain with one Hippocampi on each side of the hemisphere.
The structure and role in memory formation
The Hippocampus is one of the four structures that forms the limbic system, a system responsible for the control of emotion. The Hippocampus itself is responsible for converting short-term memory to long-term memory and in the limbic system, it is important for the processing of emotional memory based on stimulus from the Amygdala.
The idea that the Hippocampus plays a role in memory formation gained traction among researchers and the medical community when William Beecher Scoville and Brenda Milner reported on a surgery they performed on a patient named Henry Molaison in 1953. The surgical destruction of the Hippocampus was done to rid Henry’s epilepsy and although that dealt with the recurrent seizure problem, Henry suffered from anterograde (forming new memories) and retrograde amnesia (recent previous memories) afterwards.
In the following years after that, more and more reports found the same memory-impairment effect with patients who had their Hippocampus damaged (from accidents or diseases). However, distant memories in the past were not affected as they could recall childhood event, suggesting that while the Hippocampus is responsible for the consolidation of short-term memory to long-term memory, it does not actually store it. Furthermore, it also doesn’t affect procedural or implicit memory such as the skill to play musical instruments or solving puzzles.
To date, 2 other functions has been associated with the Hippocampus which are spatial memory and navigation and approach-advance conflict processing.
Diseases related to the Hippocampus
There are a few diseases that affects the Hippocampus such as:
Alzheimer’s disease – In this condition, gradual insult to the brain structure manifests as progressively worsening dementia and one of the earliest structure affected in this disease is the Hippocamus, leading to the typical manifestation of memory problems.
Chronic stress – The Hippocampus is rich in glucocorticoid receptors on its surface, a component of hormones released during stress. It is therefore extremely susceptible to stress compared to other brain structure. For instance, in patients with Post-Traumatic Stress Disorder, scans have shown that the volume of their Hippocampus decreased by around 20% compared to those without the disease and those with conditions that causes prolonged secretion of stress hormones (Cushing’s syndrome ), the Hippocampus experience atrophy much worse than other parts of the brain.
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