Brain
Amygdala
The fear and emotion processor
Overview
The amygdala is an almond-shaped cluster of nuclei deep within the temporal lobe, playing a central role in emotional processing, particularly the detection and response to threats. It rapidly appraises sensory input for emotional relevance and triggers the body's fight-or-flight response via the hypothalamus and brainstem.
Function
- Fast threat detection and fear conditioning
- Modulation of emotional memories (with hippocampus)
- Social cognition: reading emotional facial expressions
- Triggers fight-or-flight via hypothalamic-pituitary-adrenal axis
- Processes reward and positive emotions as well as fear
Key Facts
- The amygdala processes emotional stimuli faster than the cortex (the "low road")
- Bilateral amygdala damage (Urbach-Wiethe disease) eliminates fear responses
- PTSD is associated with hyperactivity of the amygdala
- Women tend to have larger amygdalae that are more emotionally reactive
Key Substructures
- Basolateral complex (BLA): receives sensory input; site of fear learning and emotional associations
- Central nucleus: primary output nucleus, triggers fight-or-flight via hypothalamus and brainstem
- Medial nucleus: processes pheromone signals; connects to olfactory system
- Basomedial nucleus: integrates emotional context with memory and decision-making
Clinical Notes
- Bilateral damage (Urbach-Wiethe disease) nearly eliminates fear and risk aversion
- PTSD involves chronic hyperactivation of the amygdala to trauma-related cues
- Amygdala hyperactivity underlies many anxiety disorders including social anxiety
- Damage impairs ability to recognize fearful and threatening facial expressions