Amygdala

Fear and the Amygdala

Fear
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The amygdala is an almond-shaped mass of nuclei (mass of cells) located deep within the temporal lobes of the brain. There are two amygdalae, one situated in each brain hemisphere. The amygdala is a limbic system structure that is involved in many of our emotions and motivations, particularly those that are related to survival. It is involved in the processing of emotions such as fear, anger, and pleasure.

The amygdala is also responsible for determining what memories are stored and where the memories are stored in the brain. It is thought that this determination is based on how huge an emotional response an event evokes.

Amygdala and Fear

The amygdala is involved in autonomic responses associated with fear and hormonal secretions. Scientific studies of the amygdala have led to the discovery of the location of neurons in the amygdala that are responsible for fear conditioning. Fear conditioning is an associative learning process by which we learn through repeated experiences to fear something. Our experiences can cause brain circuits to change and form new memories. For example, when we hear an unpleasant sound, the amygdala heightens our perception of the sound. This heightened perception is deemed distressing and memories are formed associating the sound with unpleasantness.

If the noise startles us, we have an automatic flight or fight response.

This response involves the activation of the sympathetic division of the peripheral nervous system. Activation of the nerves of the sympathetic division results in accelerated heart rate, dilated pupils, increase in metabolic rate, and increase in blood flow to the muscles. This activity is coordinated by the amygdala and allows us to respond appropriately to danger.

Function

The amygdala is involved in several functions of the body including:

  • Arousal
  • Autonomic Responses Associated with Fear
  • Emotional Responses
  • Hormonal Secretions
  • Memory

Sensory Information

The amygdala receives sensory information from the thalamus and from the cerebral cortex. The thalamus is also a limbic system structure and it connects areas of the cerebral cortex that are involved in sensory perception and movement with other parts of the brain and spinal cord that also have a role in sensation and movement. The cerebral cortex processes sensory information obtained from vision, hearing, and other senses and is involved in decision-making, problem-solving, and planning.

Location

Directionally, the amygdala is located deep within the temporal lobes, medial to the hypothalamus and adjacent to the hippocampus.

Amygdala Disorders

Hyperactivity of the amygdala or having one amygdala that is smaller than the other has been associated with fear and anxiety disorders. Fear is an emotional and physical response to danger. Anxiety is a psychological response to something that is perceived as dangerous. Anxiety can lead to panic attacks that occur when the amygdala sends signals that a person is in danger, even when there is no real threat.

Anxiety disorders that are associated with the amygdala include Obsessive Compulsive Disorder (OCD), Post-Traumatic Stress Disorder (PTSD), Borderline Personality Disorder (BPD), and social anxiety disorder.