What is Amygdala? What is its Function & Structure?

Amygdala: What It Is? What is The Function?

Author: Josna Lewis

The amygdala is a small part of the brain and has vast functions. It is part of the limbic system, linked with the processing of emotions, behavior, and memory. It also possesses control over reaction to stress, attention, and sexual instinct.

The amygdala means “almonds” derived from the Greek word “amygdale”, owing to the almond-shaped structure formed by the many nuclei. The amygdala was first identified and named after Karl Friedrich Burdach in 1822.

The fear we experience when we watch a horror movie or when we stand at the edge of a cliff, the attraction you have to someone may be partial due to the amygdala. It is responsible for fear, anxiety, aggression, sexual attraction, and pleasure.

Structure

The amygdala lies between the temporal lobes, present on either side of the hemisphere. anterior to the hippocampus and anterior tip of the inferior horn of the lateral ventricle and forms part of the surface of the uncus.

The amygdala comprises 13 nuclei, they are then sorted into five groups basolateral nuclei, cortical-like nuclei, central nuclei, and other amygdaloid nuclei.

The lateral nucleus receives input from the sensory cortices (information about sensory stimuli e.g. Vision and hearing). The auditory stimuli from the subcortical region located in the thalamus are directed to the amygdala. The olfactory stimuli flow into the cortical and medial amygdala from the olfactory bulb that senses smell. The amygdala also receives additional sensory stimuli from various other nuclei present.

The output of the central amygdala projects to subcortical structure and mediates autonomic, physiological, and behavioral expressions. While the basal nuclei project the output signal to the cerebral cortex and modulate the cognitive processes.

Hemispheres

The amygdala lies in either of the hemispheres.

Left Hemisphere

Studies suggest that the left amygdala induces reward responses that elicit both pleasant (happiness) and unpleasant (fear, anxiety, or sadness) emotions. It mainly deals with declarative memory i.e. information or memory of the previous events

Right Hemisphere

In contrast, the right side of the brain processes only negative responses, especially fear stimuli and responses. This emotional response conditions the individual to avoid this fear or threats.

Functions

The following are the structures that send fibers to the amygdala:

• Olfactory bulb
• Orbitofrontal cortex
• Cingulate gyrus
• Basal forebrain
• Medial thalamus
• Hypothalamus
• Brainstem

Emotional Learning

Amygdalae plays the primary role in the formation and storage of memories associated with various emotional events. Stimuli and memory associate e.g. producing a loud banging noise (aversive stimulus) each time a person is shown an image of a particular stranger’s face (neutral stimulus), which produces a conditioned fear (negative) response.

Amygdalae also influence appetitive (positive) responses, researchers suggest that different nuclei are responsible for the appetitive response.  The amygdala influences cognitive processes such as memory formation, decision-making, attention, and social behavior. Any damage/ lesions to the amygdala may lead to impairment in these events.

Memory Modulation

Long-term memory is not formed instantaneously, the information regarding the event (fear, happiness, learning, etc) is compiled gradually for long-term storage, via long-term potentiation. The basolateral nuclei are involved in mediating the effects of emotional arousal on the strength of the memory of the event. Compassion meditation in Buddhist monks modulates their amygdala activity.

Aggression

Animal studies suggest that stimulating the amygdala increases both sexual and aggressive behavior. Studies using brain lesions indicate that damage to the amygdala may have the opposite effect.

Social behaviour

The amygdala may contribute to social connections. It is responsible for facial recognition and allows to respond accordingly. Individuals with larger amygdala has more larger and complex social networks which also determine individuals’ emotional intelligence and greater societal integration and cooperation.

Reward Processing

While often associated with negative emotions like fear, the amygdala also plays a role in processing positive emotions and rewards. It is involved in assessing the emotional significance of rewarding stimuli and motivating behavior accordingly.

Decision Making

The amygdala influences decision-making processes by integrating emotional information with cognitive processing. It can bias decision-making toward actions that are perceived as emotionally salient or relevant.

What is the Amygdala hijack?

Output of sensory stimuli is first received by the thalamus, and the thalamus directs it to the amygdala or emotional/ irrational brain, while other signals are perceived by the neocortex or thinking/ rational brain. If the record of information in the hippocampus directs the amygdala to that stimulus to be a flight/ fight situation the amygdala takes over the rational brain causing “Amygdala hijack”.

Occurs when strong emotions “take over” the thinking ability of the brain. It happens when strong emotions- fear, excitement, aggression- impair the prefrontal cortex that regulates rational thinking.

While this process is helpful in an actual life-and-death situation, this survival mechanism allows us to react to danger before the rational brain has time to process it. In brief, it means that you react to a situation irrationally out of emotions, which you may later regret.

E.g. You get a call that your loved one is in the emergency room, but you are so stressed you miss the details.

Dysfunction of Amygdala

According to studies, the left side of the amygdala is associated with mental health conditions. Individuals with severe phobias show a close correlation with increased amygdala response.

Anxiety Disorders

The amygdala’s role in processing fear and anxiety makes it a key player in anxiety disorders such as generalized anxiety disorder (GAD), panic disorder, social anxiety disorder (SAD), and specific phobias. Overactivity or dysregulation of the amygdala can lead to heightened fear responses and excessive anxiety.

Post-Traumatic Stress Disorder (PTSD)

PTSD often involves dysfunction in the amygdala, which contributes to the persistent re-experiencing of traumatic memories, heightened arousal, and exaggerated fear responses. Changes in amygdala structure and function have been observed in individuals with PTSD.

Depression

Depression is a complex disorder involving multiple brain regions and neurotransmitter systems, abnormalities in amygdala function have been implicated in the development and maintenance of depressive symptoms. Overactivity of the amygdala, particularly in response to negative emotional stimuli, may contribute to depressive symptoms such as persistent sadness, hopelessness, and anhedonia (loss of interest in activities).

Bipolar Disorder

Both hyperactivity and dysfunction in the amygdala have been associated with bipolar disorder, a mood disorder characterized by episodes of mania and depression. Abnormalities in amygdala function may contribute to mood dysregulation and emotional instability seen in bipolar disorder.

Autism Spectrum Disorder (ASD)

Research suggests that individuals with ASD may have abnormalities in amygdala structure and function, which could contribute to difficulties in social interaction, emotional processing, and sensory sensitivities characteristic of the disorder.

Phobias

Specific phobias refer to extreme and illogical fears of certain objects or situations.. Dysfunction in the amygdala’s fear-processing circuits may contribute to the development and persistence of phobias by amplifying fear responses to certain stimuli.

Conclusion

In conclusion, the amygdala plays a pivotal role in processing emotional responses, influencing behaviors such as fear, aggression, and social interactions. Its function is critical in memory modulation, decision-making, and the processing of both positive and negative emotional stimuli. Dysfunctions or abnormalities in the amygdala are linked to various mental health conditions, including anxiety disorders, PTSD, depression, bipolar disorder, and ASD, highlighting its significance in both emotional regulation and psychiatric disorders.

Understanding the amygdala’s complexities provides valuable insights into the biological underpinnings of emotions and their impact on human behavior and mental health.

References

1. https://en.wikipedia.org/wiki/Amygdala
2. https://www.simplypsychology.org/amygdala.html
3. AbuHasan Q, Reddy V, Siddiqui W. Neuroanatomy, Amygdala. In: StatPearls. StatPearls Publishing, Treasure Island (FL); 2023. PMID: 30725787.
4. https://en.wikipedia.org/wiki/Amygdala_hijack
5. https://www.verywellmind.com/the-role-of-the-amygdala-in-human-behavior-and-emotion-7499223