Is the amygdala really the brain's fear center?
A woman with no working amygdalae did not flinch at snakes or haunted houses. Yet a breath of carbon dioxide brought on panic.
▶ Start the storyIs the amygdala really the brain's fear center? The amygdala, a paired nuclear complex in the cerebral hemispheres, is often described that way. The textbook role is real: the amygdala has a primary role in the processing of memory, decision-making and emotional responses, including fear, anxiety and aggression. But the full story is more interesting.
The best-known evidence is a woman known as S.M. Since late childhood she has had complete destruction of the amygdala on both sides, a consequence of a very rare genetic disorder called Urbach-Wiethe disease. When researchers exposed her to snakes and spiders, a haunted attraction and scary film clips, she showed no fear, only interest, curiosity and excitement. She cannot recognize fear in other people's faces. The disproportionate number of traumatic events in her life has been attributed to a combination of living in a dangerous area and a marked impairment in detecting looming threats.
Step 1: Snakes, spiders, haunted house
No fear; interest and excitement
Step 2: Other people's faces
Cannot recognise fear in them
Step 3: Carbon dioxide breathing
Fear and panic, more intense than controls
Yet S.M. is not fearless. In carbon dioxide breathing tests that simulate suffocation, she and other patients with bilateral amygdala damage felt fear and panic of greater intensity than healthy controls, feelings they described as completely novel to them.
The label is disputed. The amygdala is not exclusively a fear center: it also responds to various environmental stimuli and is involved in positive conditioning. Joseph LeDoux, who studied fear conditioning in rodents, argues that circuits that detect and respond to threats should not be called fear circuits, since that implies they produce the feeling of fear. In his view fear is a conscious experience that arises via cortical circuits.
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Recap
The amygdala detects and responds to threat and does much else, and whether it creates the feeling of fear is disputed.
💡 A trick to remember it · LeDoux's smoke detector: the amygdala sounds the threat alarm, and the feeling of fear, he argues, is built elsewhere.
Surprising fact · A patient with complete amygdala destruction showed no fear of snakes but felt intense panic during a carbon dioxide breathing test.
Sources (5)
No source, no claim. Every fact in this lesson (18 claims) cites at least one of these.