Functions of the Hippocampus

Bodytomy Staff Sep 30, 2018
Though it is a very small part of the brain, hippocampus is involved in some vital functions, especially memory formation.
It is a common fact that memory loss is one of the early signs of Alzheimer's disease, which is directly linked to brain damage. Certain parts of the brain are found affected, during the initial stages of the disease. A small part of the brain, called hippocampus, is one among them.
Thus damage to the hippocampus can be associated with the warning signs of Alzheimer's disease - memory problems. In short, hippocampus is believed to be involved in memory formation.

What is Hippocampus?

Image Credit: Gray's Anatomy;Derivative-Looie496/via Wikimedia Commons (PD)
We all know how important is the role played by the brain in the human body. It is among the most complex organs and is responsible for controlling almost every action in the body. Right from making movements to memorizing and thinking, the brain has an important role to play.
The brain is divided into three main parts - cerebrum, cerebellum and the brain stem. Cerebrum, which is otherwise known as cortex, is the largest part of the brain. Cerebrum has four lobes - frontal lobe, occipital lobe, parietal lobe, and temporal lobe.
Hippocampus is that brain structure, which is located in the medial temporal lobe and is attributed with some major functions.
Hippocampus and associated structures
Image Credit: Gray's Anatomy/via Wikimedia Commons (PD)

Hippocampus is a part of the limbic system, which is responsible for emotion, behavior, memory and olfaction.
Hippocampus is located in the medial temporal lobe, beneath the cortex. It has a distinct curved shape, that is compared to the shape of a seahorse. In fact, the name hippocampus is derived from the Latin name for a marine creature.
Hippocampus is a paired structure, with two identical halves that are located on the left and right sides of the brain. The volume of each half is around 3 to 3.5 cm3 in adult humans. Hippocampus is believed to be one of the oldest parts of the brain, as far as the evolutionary development of the organ is concerned.
Basic neural circuitry of the Hippocampus
Image Credit: Santiago Ramón y Cajal;derivative-Looie496/via Wikimedia Commons (PD)
When it comes to hippocampus functions, the most vital structures are the dentate gyrus (DG), hippocampus proper (consists of four zones - CA1 TO CA4), subiculum (Sub) and the entorhinal cortex (EC). The dentate gyrus and hippocampus proper are like inter-folded layers. It is the dentate gyrus region that receives input from the entorhinal cortex.
Apart from sending output to the CA3 region of hippocampus proper, dentate gyrus is also a site for production of new neurons. From CA3 region, the information is send to CA1, from where it passes to the subiculum, alveus (a thin structure that merges into fimbria), fimbria and fornix. From fornix, the information is send to other parts of the brain.

Functions of the Hippocampus

The most important function of the hippocampus is forming memories (especially episodic memories relating to personal events and related emotions) and spatial navigation. Earlier, it was thought that this structure is responsible for olfaction and this belief was later proved false.
However, studies to figure out the role of hippocampus in some olfactory responses like, memory of smell, is still underway.

Memory

Though the role of hippocampus in forming new episodic memories is still not conclusive, it is believed that this part of the brain plays a vital role in processing current information and memorizing it.
It is believed that rather than storing information, hippocampus processes new information to be stored somewhere else in the cortex. This is the reason why people retain old memories even though the hippocampus gets damaged. However, they fail to memorize current events and make new memories. This happens to those with Alzheimer's disease.

Spatial Navigation

Hippocampus is believed to have a very active role in memorizing information about spatial orientation and navigation. This theory has been proven by studies conducted on rats and some other animals. It was revealed that in rodents, a healthy hippocampus is very much required for proper navigation. This is said to be relevant for humans too.
This could be the reason why people with Alzheimer's disease fail to remember new locations and routes. A study conducted on taxi drivers in London showed that experienced drivers (who are experts in finding new routes and shortcuts) have a bigger hippocampus, when compared to others.
Though the volume of hippocampus is similar in both drivers and general public, its posterior part was found to be slightly bigger in drivers. However, the anterior portion appeared smaller.
Hippocampus is said to be involved in a few medical conditions. Apart from Alzheimer's disease, this part of the brain is said to be involved in schizophrenia, severe depression, post-traumatic stress disorder, epilepsy and bipolar disorder.
It is also suggested that lower level of estrogen may affect hippocampus negatively. The efficiency of hippocampus may decrease with age and this could be a reason for memory problems during old age. It is also believed that stress is not good for hippocampus.
The mentioned functions are not well-defined and are still debated. In short, hippocampus is a complex brain structure, which is still a subject for various researches.