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Portrait of Amygdala

Anatomy · Brain & nerves

Amygdala

Greek 'almond'

Brain · limbic system, temporal lobe

An almond-shaped cluster of nuclei buried in the front of each temporal lobe, just in front of the hippocampus. It is central to processing emotion, above all fear, and to attaching emotional significance to memories. It helps trigger the fight-or-flight response by signalling to the hypothalamus and brainstem.

How to spot them

  • ▸Two almond-sized clusters of grey matter, one deep in each temporal lobe, in front of the tip of the lower ventricular horn
  • ▸Lies just in front of the hippocampus, at the end of the tail of the caudate nucleus
  • ▸A group of nuclei rather than a single lump: basolateral, central and corticomedial groups
  • ▸A key part of the limbic system, linked by a curved fibre bundle (the stria terminalis) to the hypothalamus

What to know

Named for its resemblance to a nut: the Greek word means 'almond'

Amygdala — amygdale, almond.

The brain's alarm centre, quick to register threat and trigger the fight-or-flight response

Amygdala — the centre of fear processing.

A patient with a rare genetic disorder that calcified these structures could feel no fear, even facing a snake or a knife

Amygdala — the case of patient S.M. with Urbach–Wiethe disease.

Bilateral removal in rhesus monkeys in 1939 produced tameness, hypersexuality and a compulsion to put everything in the mouth

Amygdala — Klüver–Bucy syndrome, from bilateral temporal lobe damage.

Tags memories with emotion, so that a frightening event is remembered vividly

Amygdala — emotional memory, working with the hippocampus.

Fear conditioning in rats — pairing a tone with a shock — was mapped onto it by Joseph LeDoux

Amygdala — the 'low road' for fear.

Sits just in front of the seahorse-shaped structure of the medial temporal lobe

Amygdala — anterior to the hippocampus.

Key ideas

  • It can respond to a threat before the cortex has fully identified it — the fast, crude 'low road' that LeDoux described.
  • It works with the hippocampus: the hippocampus records where and when, the amygdala records how it felt.

Quick-fire facts

  • •Its name is from the Greek amygdale, 'almond'; Karl Burdach first described it in 1819
  • •There is one in each temporal lobe; each is a complex of several distinct nuclei
  • •Klüver–Bucy syndrome (1939) follows bilateral removal of the temporal lobes in monkeys
  • •Patient S.M., with Urbach–Wiethe disease, had calcified amygdalae and was unable to experience fear normally
  • •It projects to the hypothalamus and brainstem to drive the autonomic response to fear
  • •Part of the limbic system, alongside the hippocampus, cingulate gyrus and hypothalamus
  • •Hyperactivity of the amygdala is reported in anxiety disorders and post-traumatic stress disorder
  • •'Amygdala hijack' is a popular term (Daniel Goleman) for an emotional reaction that overrides reasoning, though it is not a formal medical term

Drill it — 7 cards

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Sources