A threat alarm
The name comes from the Greek word for almond, and the structure was first described in the early 19th century by the German anatomist Karl Friedrich Burdach; despite the similar-sounding Latin, it has nothing to do with the tonsils. Signals from the eyes and ears pass through the thalamus and reach the amygdala very quickly. American neuroscientist Joseph LeDoux described a fast "low road" that bypasses the cortex and a slower "high road" that arrives after detailed cortical analysis, which is why you flinch at a curved stick in the grass before realising it is not a snake. When the amygdala detects a threat it signals the hypothalamus and brainstem to release adrenaline and cortisol, producing the racing heart and freezing of the fight-or-flight response.
Learning fear and emotional memory
Play a tone to a rat and follow it a few times with a mild shock, and soon the tone alone makes the animal freeze. Animal studies showed that this fear conditioning takes place in the amygdala. In the late 1930s Klüver and Bucy reported that monkeys with temporal-lobe damage including the amygdala lost their fear, for instance of snakes. In humans, the best-known case is patient S.M., whose amygdalae were destroyed by a rare genetic disease: she handled snakes and spiders and watched horror films with almost no fear, and struggled to recognise fearful facial expressions. The amygdala also signals the hippocampus to store emotionally arousing experiences more firmly, which is why frightening or surprising events stay vivid longer than ordinary ones.
Anxiety, PTSD and the "amygdala hijack"
Brain imaging of people with post-traumatic stress disorder, generalised anxiety disorder and specific phobias tends to show stronger amygdala responses to threat-related cues and weaker calming control from the prefrontal cortex. Exposure therapy, a form of cognitive behavioural therapy in which people repeatedly face what they fear in safety, works less by erasing fear memories than by layering new safety learning on top of them. In 1995 Daniel Goleman coined the phrase "amygdala hijack" for moments when anger or fear overwhelms rational judgement; it is a popular metaphor, not a medical term. The amygdala is involved not only in fear but also in reward, social signals and directing attention to important stimuli.
FAQ
- Does a bigger amygdala mean more fear?
- Size alone does not determine personality. Some studies link anxious temperament to amygdala reactivity, but individual differences are large and connections with regions such as the prefrontal cortex matter too.
- Can you calm the amygdala?
- Slow breathing with long exhalations, regular exercise and sleep, and mindfulness training have been shown to reduce stress responses. If anxiety interferes with daily life, see a mental health professional.
Sources reviewed: 2026-10-26
References
- LeDoux, J. E. (2000). Emotion circuits in the brain. Annual Review of Neuroscience, 23, 155–184.
- Klüver, H., & Bucy, P. C. (1939). Preliminary analysis of functions of the temporal lobes in monkeys. Archives of Neurology and Psychiatry, 42(6), 979–1000.
- Feinstein, J. S., Adolphs, R., Damasio, A., & Tranel, D. (2011). The human amygdala and the induction and experience of fear. Current Biology, 21(1), 34–38.
- McGaugh, J. L. (2004). The amygdala modulates the consolidation of memories of emotionally arousing experiences. Annual Review of Neuroscience, 27, 1–28.