Hippocampal formation: parts and functions

How are our memories formed? How are we able to remember how to get each to our home or workplace? These functions that we perform unconsciously, without stopping to think about them, are possible thanks to brain structures such as the hippocampal formation.

Throughout the article we will talk about this complex brain structure, the organs that make it up and how scientific research has developed various theories around the functions of is.

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What is the hippocampal formation?

In neuroanatomy, hippocampal formation refers to a brain structure located in the medial temporal lobe. Although within the field of research itself there are discrepancies about which organs or specific brain regions form this structure, most agree that at least the dentate gyrus, hippocampus and subiculum are included within this classification. However, other areas such as the presubiculum, the parasubiculum and the entorhinal cortex are the subject of discussion, since not all authors recognize them as part of the hippocampal formation.

The main functions of the regions that make up the hippocampal formation are related to memory processes, navigation and spatial orientation, and the control of attention.

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Historical tour

During the s. In the 19th and early 20th centuries, research on hippocampal formation, more specifically the hippocampus, pointed to the idea that it exerted some kind of role in the olfactory system.

Furthermore, in 1937, research by scientists such as Papez or Klüver and Bucy began to develop the hypothesis that hippocampal formation played an important role in the responses emotional However, today there is little support for the idea that these structures are directly involved with emotional processes, since emotional memory is more related to amygdala.

Although it was not until centuries later that the relationship between the structures was recognized hippocampals and memory processes, in 1900 the Russian-born neurologist Vladimir Bekhterev He discovered an association between significant memory deficit and softening of the hippocampus and cortical tissue.

In the same way, in 1957 the researchers Scoville and Milner also reported symptoms related to memory loss in patients with temporal lobe lesions medial. These were some of the first investigations thanks to which we now know that the hippocampal formation plays an essential role in some memory processes.

Finally, animal studies carried out in 1970 also established the relationship between the hippocampus and spatial coding. However, this association is still widely debated by the scientific community.

Parts of the hippocampal formation

As indicated at the beginning of the article, the hippocampal formation is made up of various brain structures. These structures are the dentate gyrus, the hippocampus, and the subiculum.

1. Serrated turn

The gyrus or dentate gyrus is a part of the hippocampal formation to which an important role is attributed to it within episodic memory, as well as in exploring new environments. In addition to the formation of memories, it is also hypothesized that the dentate gyrus intervenes in some way in the regulation of emotions.

Memory

The dentate gyrus is believed to be one of the few brain regions in which the neurogenesis, that is, the birth of new neurons. It is also hypothesized that this neurogenesis facilitates or enhances the formation of new memoriesas well as it is associated with the improvement of spatial memory.

Stress and depression

Other aspects in which the dentate gyrus plays a functional role is stress and depression. Some research has shown that neurogenesis increases in response to antidepressant treatment; as well as a relationship between the physiological effects of stress and the inhibition of the birth of new neurons has been established.

Finally, it is known that both endogenous glucocorticoids that are generated as a product of stress can play psychosis and depression, implying that neurogenesis in the dentate gyrus may play a role major in the modulation of the symptoms of these emotional responses.

Spatial behavior

Animal studies have shown that after damage or destruction of the cells of the dentate gyrus there is extreme difficulty in finding one's way through a labyrinth. Specifically, there are problems when it comes to consolidate the information learned about a specific placeTherefore, it is hypothesized that injuries to the dentate gyrus can cause alterations in spatial memory.

2. Hippocampus

The second and most important of the organs of the hippocampal formation is the hippocampus, one of the main structures of the mammalian brain located within the medial or medial part of the temporal lobe.

The main functions of the hippocampus are related to both memory processes and spatial memory and orientation. Let's see what they are.

Memory

According to general consensus, the hippocampus is one of those responsible for the formation of new memories, both episodic and autobiographical. In addition, an increase in hippocampal activity has been shown in the presence of novel stimuli.

Lesions in this structure do not usually affect other types of memory formation related to the acquisition of motor or cognitive skills, but in the training of new memories. That is, damage or deterioration of the hippocampus can lead to the appearance of anterograde amnesia.

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Spatial memory and orientation

As in the dentate gyrus, studies carried out in animals have shown that some neurons in the hippocampus generate a series of electrical potentials when the animal passes through specific areas of its environment.

Although the evidence for this activity in primate brains is very limited, this activity neuronal memory may suggest that the hippocampus also has certain responsibilities for spatial memory and orientation.

3. Subiculum

Finally, the structure known as subiculum it is the lowest part of the hippocampal formation.

Although this structure is still under investigation, it is speculated that the subiculum is involved in some cases of epilepsy. Besides, also It has been related to working memory and spatial orientation, as well as it is suggested that it may be involved in some processes of drug addiction.