Hippocampus in the Human Brain

Hippocampus is the part of the brain that is found in the inner folds of the bottom middle section of the brain known as the temporal lobe. Humans got to know about the hippocampus 4 centuries ago and it is one of the most studied parts of the brain. The shape of the hippocampus is related to the sea horse. After knowing about the hippocampus, it has helped researchers understand how memory works.

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 The hippocampus meaning in the Greek word is horse monster as it is derived from the Greek word hippos(horse) and kampos(monster). 

Hippocampus located in the allocortex,  with the neural projections in the neocortex and as well as the primates. The hippocampus, like the medial pallium, is the structure found in all vertebrates. The two main parts of hippocampus are the Cornu ammonis (hippocampus proper) and dentate gyrus. 

Hippocampus Function

Some of the important hippocampus functions are discussed below:

• The hippocampus is part of the limbic system. And it is associated with the functions of feeling, expression and reacting.

• The limbic system is situated on the edge of the cortex. It mainly includes the hypothalamus and the amygdala.

• These structures help control different bodily functions, such as the endocrine system. Which is commonly known as the “fight or flight” reaction.

Role of the Hippocampus in Memory 

According to psychologists and neuroscientists, the hippocampus plays an important role in the formation of new memories about experienced events. Part of this function is hippocampal involvement in the detection of new places and stimuli. Some of the researchers say that the hippocampus is a part of a larger medial temporal lobe memory system, which is responsible for general declarative memory. It also encodes the emotional context from the amygdala, this is partly why returning to a location where an emotional event occurred may evoke that emotion. There is a deep emotional connection between episodic memories and places of the human.

Anatomy of Hippocampus

The primary structure within the limbic system includes the thalamus, basal ganglia, cingulate gyrus, amygdala hippocampus and hypothalamus. 

The anatomy of the hippocampus is of chief importance to perform its function.  The hippocampus receives input and sends output to the rest of the brain through a structure known as the entorhinal cortex. It is located beneath the anterior region of the hippocampus and is composed of several subregions like cornu ammonis (CA1–4), the dentate gyrus, and the subiculum.

Sources of Input 

It receives input from the modulatory neurotransmitter system, which includes serotonin, norepinephrine, and dopamine systems. Hippocampus receives cholinergic input from the medial septum, which regulates the hippocampus physiological state. The medial septum is involved in setting one of the critical oscillatory rhythms in the hippocampus known as the theta rhythms. This rhythm is associated with hippocampal function. 

Due to the bilateral symmetry, the brain has a hippocampus in each of the cerebral hemispheres; if the hippocampus is damaged in one hemisphere, it leaves the structure intact in the other hemisphere. Severe damage to the hippocampus in both the hemispheres will result in profound difficulty in forming new memories and it also affects the memories formed before the damage occurred. The retrograde effect normally extends many years before the brain gets damaged, only in rare cases older memories of the brain remain. 

The retention of the older memories in the brain leads to the idea that over time, it involves the transfer of older memories out of the hippocampus to other parts of the brain.  The experiment was performed using intrahippocampal transplantation of hippocampal cells in the primates with neurotoxic lesions of the hippocampus. This shows that the hippocampus is important for the formation and recall of the memory, but not for the storage of memories. If the volume of the various parts of the hippocampus is decreased it leads to specific memory impairments. Speaking particularly, the efficiency of verbal memory retention is related to the anterior parts of the right and left hippocampus. The hippocampus in the right head is more involved in executive functions and regulation during verbal memory recall and the tail of the left hippocampus is closely related to verbal memory capacity.

Do You Know?

What diseases are associated with the hippocampus? Some of the common conditions in which atrophy of the human hippocampus has been reported are Alzheimer's disease, Epilepsy, Hypertension, Cushing's Disease and also in some of the other diseases.