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Amygdala: Structure, Characteristics and Functions
The amygdala is a structure of the brain that is involved in emotional reactions, anger, fear, sexual behavior or emotional memory, among other functions. But what does an injury to it entail? With what disorders is its deficit related?
The amygdala is an almond-shaped structure located in the medial temporal lobe. According to a study by Sánchez-Navarro et al. (2004), it is a fundamental structure in emotions, and more specifically, in the response to stimuli with negative content.
This structure is also related to fear, and it is what largely explains the survival of the species. And it is that the amygdala has allowed our ancestors to detect possible dangers and activate fight or flight mechanisms.
In addition, it integrates emotions and autonomous responses and allows us to emit or inhibit emotional responses. But what other functions does the amygdala have? What else do we know about it?
Amygdala: definition, structure and characteristics
The amygdala, also called the tonsillar body or tonsil complex, is a brain structure that is part of the limbic system. It is formed by a set of neurons that are related to each other in a complex way, and that give rise to a differentiable structure at the anatomical level.
It is shaped like an almond, and is located in the inner part of the medial temporal lobe. The amygdala has connections to the vast majority of areas of the brain, that is, it is related to many areas of the central nervous system.
Key structure for survival
Thus, it is a highly relevant nucleus, which affects the entire nervous system and the functionality of the organism. It is a structure that was very key to the survival of our ancestors.
This is because its main function is the integration of emotions with the response patterns that correspond to them. It allows executing physiological responses and preparing behavioral responses, among many other functions.
Located in the temporal lobe
The temporal lobe, which is the lobe where the amygdala is located, is located on the lower side of the brain (at the level of the ears). It is responsible for integrating, in a global way, a good part of the sensory information that comes to us through the senses.
It also processes language and is highly involved in hearing and auditory memory. Thus, for example, when we listen to music or listen to someone speak, the temporal lobe is responsible for deciphering the information.
Relationship with other structures
The amygdala has cortical inputs that provide information about highly processed visual, somatosensory, visceral sensory, and auditory stimuli.
This differentiates it from another structure, the hypothalamus, which is the recipient of poorly processed visceral sensory input. On the other hand, the amygdala receives sensory input directly, from some nuclei that are located in: the thalamus, the olfactory bulb and the sensory relays of the brain stem.
These afferences allow you to respond to stimuli of different sensory modalities: visual, auditory, taste, olfactory and somatosensory.
Functions of the amygdala
The main function of the amygdala is to process and store emotional reactions. These are essential for the survival of the individual, and that is why it is such an important primitive structure.
But what else is the amygdala in charge of? How is it related to sexuality or eating, for example?
Form emotional memory
Thanks to the amygdala we are also able to form and store the memories that we associate with certain emotional events. Thus, we could say that memories impregnated with emotions are possible thanks to this structure.
In other words, the amygdala allows us to associate what we experience with gratifying or aversion sensations, and this is what ends up being defined as emotional memory.
Value emotional experiences
We have seen how the amygdala is closely related to emotions. More specifically, we can say that it is very involved in assessing the meaning we attribute to experiences on an emotional level.
In addition, it coordinates areas of somatic expression of emotions and the cerebral cortex, which is responsible for the conscious feeling.
Control emotions and fear
The amygdala is considered a fundamental brain nucleus for controlling emotions and feelings. In addition, it also manages, coordinates and controls the responses of fear and satisfaction.
Fight or flight reaction
In relation to fear, we know that the amygdala allows us to react after perceiving a stimulus as potentially threatening to our physical integrity. Thus, it stimulates the fight or flight reaction.
This is possible because the amygdala is also responsible for receiving signals of potential danger. Injuries to this structure can cause very aggressive reactions, as well as loss of fear.
In addition to enabling people’s emotional reactions, the amygdala is also responsible for inhibiting them. This is thanks to its connections with the frontal lobe.
Thus, it is a structure that manages the emission or inhibition of emotional responses or reactions (at the conscious and unconscious level).
Regulates sexual behavior
The amygdala is also related to sexual behavior. It allows the association of different stimuli with pleasure, and links the emotions between people.
In addition, it also enables the maintenance of intimate relationships thanks to this emotional bonding.
The amygdala also has an influence on the control of food intake and its perception. Thus, it is linked to the satiety response. Thanks to its relationship with this physiological function, it allows the maintenance of body homeostasis.
Enables social cognition (and other functions)
According to an article by Ruggieri (2014), the amygdala is also related to long-term memory, orientation towards social stimulus and perception of gaze orientation.
In addition, it is very involved in face recognition (especially fearful faces). Thus, it is also related to certain social functions, which allow us to understand various emotional states. This understanding provides us with adequate social cognition.
Components of the amygdala
The amygdala, or tonsil complex, is a structure that can be divided into different subcomponents. Which of them are the most important? Let’s see its three main nuclei:
The corticomedial nucleus is involved in the uptake of pheromones, and participates in the control of male and female sexual behavior. It is involved in hormonal control and, in addition, it is what allows us to emit the satiety response during intake.
Of the entire amygdala, the central nucleus is the region that is most involved in the expression of the emotional response, both at a physiological and physical level. Thus, it produces the responses we feel to emotions.
It is linked to the autonomic nervous system and allows us to perform behaviors in response to the sensations that perceptions produce.
Finally, the basolateral nuclei of the amygdala are primarily involved in the control of intake. In addition, they are involved in learning (and performing) learned emotional responses, such as fear of certain stimuli.
Dysfunctions in the amygdala: what disorders are they related to?
As stated in the Ruggieri study, amygdala dysfunctions have been associated with neurodevelopmental disorders and with “neurocognitive and behavioral alterations in specific neurogenetic entities.”
Thus, according to the study itself, we can divide these types of disorders related to amygdala dysfunction into two groups:
- Developmental and behavioral disorders: autism, anxiety disorders, bipolar disorder, alexithymia, and anorexia nervosa.
- Specific neurogenetic entities: Fragile X syndrome, Rett syndrome, Prader-Willi syndrome, and Williams syndrome.
As we have seen, and as stated by Ruggieri (2014) in his study, the amygdala is related to the recognition of the affective or emotional meaning of stimuli, to emotional memory, to fear and aggressiveness, to emotional reactions…
Thus, it is involved in multiple functions, both physiological and social and emotional. Its injury or deficit can cause, among other symptoms, the absence of fear, which can lead to impulsive or reckless behavior.
It has also been linked to autism and other neurodevelopmental (or behavioral) disorders.