Amygdala: fear and emotional processing
The amygdala is an almond-shaped cluster of nerve cells in the temporal lobe that links a threat to a fear response and gives the threat its emotional weight.
Remember
The amygdala learns which cues signal threat and triggers the fear response, and damage to it, especially on both sides, blunts fear learning and fear responses.
Memory aid
the amygdala is the brain's alarm bell, ringing when something threatening is detected
The alarm bell rings when something threatening is detected, just as the amygdala triggers the fear response.
The limbic system is a network of linked structures near the centre of the brain that manages emotion, motivation and memory. There is some debate about which structures belong, but the usual list is the amygdala, the hippocampus (which forms new memories), the cingulate gyrus (linked to emotion and attention), the fornix (a bundle of nerve fibres carrying signals out of the hippocampus), the hypothalamus (control of hormones and the autonomic nervous system) and the thalamus (a relay station for sensory information).
The amygdala receives sensory information and attaches emotional salience to it, meaning a sense of how important or threatening something is. It passes its output to the hypothalamus and brainstem, which produce the automatic body response to danger, such as sweating and a faster heartbeat.
Fear conditioning is a form of learning in which a neutral cue, such as a sound or a place, comes to trigger fear because it has been paired with something threatening. The amygdala forms this learned link and then triggers the fear response when the cue returns.
A lesion (damage) in the amygdala, especially on both sides, blunts fear learning and fear responses. People with selective bilateral damage show lower fear sensitivity and a selective impairment in recognising fearful expressions, while general memory, attention and executive function (planning and decision making) can stay intact.
The amygdala also connects strongly with the prefrontal cortex, the front part of the frontal lobe that helps control emotional responses. Dysfunction in this circuit is linked to altered mood and to anxiety disorders.
Key facts
- Structure
- an almond-shaped cluster of nerve cells deep in the temporal lobe.
- Main job
- it detects threat and assigns emotional salience (how important or threatening something feels).
- Fear conditioning
- a neutral cue paired with a threat comes to provoke fear on its own.
- Output
- it connects with the hypothalamus and brainstem to drive the body's reaction to danger.
- Bilateral damage
- reduced fear and impaired recognition of fearful faces, with memory, attention and executive function relatively intact.
- Illness link
- abnormal amygdala function is linked to anxiety disorders, and limbic dysfunction is thought to contribute to mood disorders.
Exam traps
- The hippocampus does not generate the fear response itself: it forms new memories of facts and events and helps tie a fear memory to its place or context.
- The hypothalamus controls the automatic and hormonal outputs that accompany emotion, but it does not itself recognise emotion in faces.
- The fornix does not itself process emotion, because it is a bundle of nerve fibres that connects the hippocampus to other limbic structures and carries signals.
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