Brain amygdala: structure and functions

Surprise, afraid, anguish, affection, affection, joy, excitement... All these words denote different emotions that we all feel on a day-to-day basis..

These are reactions that we have to stimuli that can come from both outside (for example, seeing a spider, a baby or that you communicate your long-awaited rise) as well as inside yourself (a thought or memory that makes you suffer or feel happy). These reactions, at the brain level, depend on a series of circuits that are capable of organizing and connecting perception and emotion, the main system in charge of this being the limbic system, and within this system, the amygdala being one of the main nuclei.

In this article we are going to focus on this structure, the amygdala, in order to visualize what it is and some of its main functions.

What is the amygdala?

The amygdala is a subcortical structure located in the inner part of the medial temporal lobe. This element has connections with the vast majority of the brain, being a nucleus of special relevance that can affect the entire nervous system and the functionality of the organism.

It is a key element for survival, because its main function is to integrate emotions with response patterns corresponding to these, provoking a response at the physiological level or the preparation of a behavioral response. Likewise, it is in charge of coordinating the areas that notice the somatic expression of emotion and the cerebral cortex in charge of the conscious feeling, which has a highly relevant role in assessing the emotional meaning of the experiences.

The amygdala is thus the main core of emotion control and feelings in the brain, also controlling the responses of satisfaction or fear. Their connections not only produce an emotional reaction but also due to their connection with the frontal lobe it also allows the inhibition of behaviors.

However, the amygdala is not a simple "piece" of the human brain, with a predictable and well-known pattern of functioning. In fact, none of the brain structures are like this, but in the case of the amygdala this is even more evident, considering that is related to many other areas of the central nervous system. It is a complex structure, being an almond-shaped structure located in the limbic system of the brain. It is made up of different parts, which is sometimes also called the tonsil complex.

Parts of the tonsil complex

As we have said, the amygdala is not a uniform structure, but is divisible into various sub-elements. Among them, the following stand out:

1. Corticomedial nucleus

This part of the amygdala complex has a great implication in the uptake of pheromones, participating to a great extent in the control of both male and female sexual behavior. Also participates in hormonal control and in the response of satiation during ingestion.

2. Basolateral nuclei

Its main participation is in the control of intake through the feeling of satiety. In the same way, their involvement in the realization and learning of learned emotional responses, such as fear reactions to different stimuli, is essential.

3. Central core

This nucleus is the one with the greatest participation in the expression of the emotional response, affecting both at a physiological level, producing the sensations and physical reactions that provoke emotions and having a great participation in the autonomic nervous system, as well as behavioral by allowing the performance of behaviors that respond to the sensations produced by the perceptions.

Likewise, this nucleus also affects the genesis and maintenance of the feelings, which differ from emotions by being patterns of thought and psychophysiological reactivity maintained over time and less specific to a specific situation.

Functions of the tonsillar complex

As mentioned, the amygdala is a complex and vital structure for survival, participating and being linked in a large number of psychological and physiological phenomena. Let's see some of them below:

1. Integration of emotions and autonomous responses

The amygdala manages the emission or inhibition of emotional responses with great precision both at a conscious and unconscious level, being its most studied function and one of the most relevant. It allows us to associate feelings of gratification or aversion to the experiences we live. Participate in both positive emotions and the reactions of joy or happiness as in other emotions of a more adaptive nature, as we will see in the next point.

2. Fear management and fight / flight reaction

In this regard, one of the main functions of the amygdala and the fact that it is a key piece of survival is fear management. At a phylogenetic level, this nucleus has allowed the survival of our species, since it is what allows us to react after perceiving a potentially threatening stimulus to physical integrity, stimulating or inhibiting the response of fight / flight. In fact, injuries to the amygdala can cause extremely aggressive reactions and loss of fear, with all the repercussions that the absence of this feeling can have.

3. Emotional learning

Associative and conditioned learning are also largely influenced by the action of the amygdala. This structure allows the choice of strategies to apply in the presence of stimuli, as well as detecting situations in which these strategies are also applicable. This is due to the link between emotion and cognition, as well as the maintenance of motivation by linking one's goals to specific feelings.

4. Memory

In addition to the learning process, the amygdala also affects the structuring of memories. This is due to the association of memories with emotional states, which allow a greater connection and fixation of the material to be remembered, allowing its consolidation.

In fact, even when the hippocampus fails and does not allow to store certain memories, the amygdala allows a certain emotional memory of a situation to be preserved, for which it is possible, for example, that one has a lot of fear of dogs (emotional memory) without remembering why this happened (due to the stress suffered in a traumatic event with a dog, that "narrative" memory of what happened has not been conserved).

5. Regulation of sexual behavior

Sexual behavior is also influenced by the action of the amygdala. In addition to allowing the association of the different stimuli with pleasure, the emotional bonding between individuals and its association with the maintenance of intimate relationships are due, among other structures, to the amygdal complex.

6. Aggressiveness

The amygdala is also linked to aggressiveness. The studies carried out so far indicate that a malfunction of this one can cause the loss of aggressive and self-defense reactions, while hyperstimulation of the tonsil complex causes reactions extremely aggressive and violent.

7. Satiation response

Another aspect in which the amygdala has some influence is in the control of intake, contributing to greatly to the maintenance of body homeostasis through its influence on the perception of satiation.

Bibliographic references:

• Kandel, E.R.; Schwartz, J.H. & Jessell, T.M. (2001). Principles of neuroscience. Fourth edition. McGraw-Hill Interamericana. Madrid.

• Méndez-Bértolo, C.; Moratti, S.; Toledano, R.; López-Sosa, F.; Martínez-Álvarez, R.; Mah, Y.H.; Vuilleumier, P.; Gil-Nagel, A. & Strange, B.A. (2016). "A fast pathway for fear in human amygdala", Nature Neuroscience.

• Nieuwenhuys, Voogd & van Huijzen (2009). The Human Central Nervous System. 4th Edition. Editorial Médica Panamericana. Madrid.