The hippocampus is one of the most important areas of the brain that is involved in the processes of learning and remembering. Since it is part of the limbic circle, there is a certain relationship with the emotional processes. The functions of the hippocampus are a target for nootropics and anxiolytics.
What is the hippocampus?
The hippocampus is a key link in the limbic system of the brain. Its structures are involved in regulating the functioning of internal organs, emotions, memory, spatial navigation and other cognitive functions.
This area of the brain is one of the most studied, but among scientists there is no consensus on the functions of the hippocampus. Some researchers believe that it is a multifunctional structure, while others reject this approach. Among scientists, the hippocampus has been repeatedly called the cornerstone of neurophysiology, which indicates the contradictory views on this structure. Perhaps the reason for this is also the fact that the limbic system is one of the oldest in evolutionary terms, which is why its multifunctionality is associated.
According to the concept of P.V. Simonov, 4 types of brain structures are distinguished in psychophysiology. Individual features of the functional interaction of the frontal cortex, hippocampus, hypothalamus and amygdala of the brain determine the formation of one of 4 types of temperament - choleric, melancholic, sanguine, and phlegmatic. Thus, the dominance of the frontal cortex over the hippocampus leads to extroversion (outward orientation of the personality), and the predominance of the hippocampus leads to introversion and orientation to the past. These two areas of the brain exhibit diametrically opposite properties.
Functions
The main functions of the hippocampus in the brain are as follows:
- Work as an olfactory center.
- Regulation of motivation and emotions.
- The transfer of information from short-term to long-term memory.
- The development of temporary conditioned reflexes.
- The formation of "spatial" memory (orientation).
- Behavioral inhibition.
Memory
Many scholars agree that the hippocampus plays an important role in the formation of new memories. This area of the brain is also involved in explicit memory associated with conscious memories, for example, events from the distant past. However, studies show that when the hippocampus is damaged, the functions of acquiring new skills (playing a musical instrument and others) are not completely lost.
There is an opinion that this part of the brain helps to keep information in a person awake, and during sleep transfers it to the cerebral cortex. The hippocampus is also activated every time at those moments when it is necessary to remember and reproduce spatial landmarks, that is, it contributes to the formation of cognitive maps or the image of a familiar objective environment.
Its other purpose is filtering the necessary information and forgetting the unnecessary. About one and a half thousand neurons that make up the structure of the hippocampus are formed daily in an adult. This corresponds to almost 2% of its volume. With age, this process decreases significantly, which is one of the reasons for the deterioration of cognitive abilities in the elderly.
Behavioral inhibition
Animal experiments during which the hippocampus was damaged showed that there is not only a suppression of the reactions that have been studied previously, but also changes in behavioral inhibition occur. They are manifested in three interconnected processes:
- inhibition of the predominant reaction to any event;
- deferral of decision;
- event protection.
A coordinated and correct course of these mechanisms protects against overload by external distractions and impulsive manifestations. In animals with a violation of this function, hyperactivity occurs.
Impact on emotions
The relationship between the hippocampus and human emotions is still not well understood. Since it is located next to the amygdala of the brain, this suggests its influence on this type of mental state. According to experiments conducted on animals, the function of the hippocampus in this case is expressed in the assessment of the novelty of external stimuli.
So, when removing the temporal lobes of the brain, along with the amygdala and the hippocampus in monkeys, they lose their sense of fear and aggressiveness. Such animals are not able to distinguish important external signals from secondary ones, as a result of which their defensive reaction decreases.
Structure
The internal structure of this area of the brain is layered. This allows us to conclude that the hippocampus functions are differentiated. The physiology of other formations associated with the analysis of a large amount of heterogeneous information (new cortex, quadrupole of the midbrain, lateral cranked bodies) confirm this fact. Hippocampal tissues are characterized by a clear ordering. This feature allows for differentiated operations with incoming information.
According to the external structure, the hippocampus is a paired structure located under the cerebral cortex in the middle zone of the temporal region of both hemispheres. It can be detected only by opening and removing the gray matter of the cortex. It got its name because of its characteristic shape in the form of a curved elongated tube similar to the body of a seahorse (from the ancient Greek word hippocampus - “seahorse”).
The internal structure of the hippocampus in the brain is very similar in all mammals. It distinguishes 3 characteristic zones:
- CA 1 - nerve cells are small, and their axons are thin and are divided into two branches at an angle of 90 °. They are also located with a high density and comprise 2 layers - superficial and deep. There is cell death in senile dementia and Alzheimer's disease.
- CA 2 - bundles of nerve fibers (or pyramids) are larger and do not form layers.
- CA 3 - the largest pyramids, in the middle part there are spine-like outgrowths.
Association with disease
Hippocampal dysfunction is observed in the following diseases and syndromes:
- Alzheimer's disease, in the early stages, manifests itself in a disorder of short-term memory, and later long-term. In this case, the size of the hippocampus decreases. Pathology most often occurs in old age (over 65 years). Gradually, the patient has a violation of speech, cognitive abilities, orientation in a familiar environment. He becomes unable to care for himself.
- Hypoxia (oxygen starvation).
- Inflammation of the brain (encephalitis).
- Temporal epilepsy. In more than 30% of cases, this disease is associated with perinatal brain damage during fetal hypoxia, infectious pathologies (measles, rubella, syphilis and others), and can also occur after birth injuries.
With the defeat of the hippocampus, Korsakov’s syndrome is observed in which a person cannot remember current events, but events from the distant past are stored in his memory. Patients are disoriented in time and space, do not know where they are, and cannot give the current date.
The effect of drugs
Drug intensification of the functions of the hippocampus is carried out using the following groups of drugs:
- Nootropics (used to eliminate memory impairment);
- anxiolytics (anxiety reduction);
- anticonvulsants (for the treatment of epileptic seizures);
- neuroprotectors (protection of nerve cells from death during oxygen starvation and an excess of calcium ions).
A special place in the stimulation of the hippocampus is occupied by those drugs that are able to change the level of acetylcholine, a neurotransmitter responsible for certain physiological reactions (muscle contraction, heart rate and blood pressure), as well as for attention and training. These drugs can have both a direct effect on the concentration of a given substance (anticholinergics, cholinomimetics), and indirectly on enzymes involved in the suppression of its activation (cholinergic agents). It is known that during training, the level of acetylcholine in the brain first gradually increases, and then decreases. The introduction of substances with acetylcholine can improve the cognitive process.