The amygdala: fear and anxiety responses
The amygdala, an almond-shaped cluster of nerve cells in the temporal lobe, detects threat and starts the body's fear and anxiety response.
Remember
Fear and anxiety point to the amygdala. Memory points to the hippocampus (which turns short-term memories into long-term ones), and the thalamus relays sensory signals.
Memory aid
amygdala sounds like alarm, and it works like the brain's alarm bell
Link the sound of the word amygdala with an alarm bell that rings when there may be danger.
The amygdala is an almond-shaped cluster of nerve cells in the temporal lobe. It belongs to the limbic system, the ring of structures on the inner surface of the brain that handles emotion, motivation, memory and learning. Within the limbic system, the amygdala is the structure particularly involved in fear and anxiety.
Think of it as the brain's threat detector. It receives sensory information, attaches emotional significance to it and judges whether a sight or sound means danger. If it does, it signals the hypothalamus (the small control centre for the autonomic, or automatic, nervous system) and the brainstem. These switch on the sympathetic fight or flight response, so the heart rate rises, breathing quickens, and adrenaline and cortisol are released.
The fear response can arrive before conscious thought. A direct route to the amygdala has been described in experiments with threatening images that a person is not consciously aware of seeing, which helps explain why fear can arrive before someone has thought about what is happening. Afterwards, the prefrontal cortex (the front of the brain, used for planning and judgement) helps to dampen the response.
Each of the other limbic structures has a job of its own. The hippocampus is mainly about memory and supplies context for a fear, but it does not itself detect the threat. The thalamus relays sensory signals towards the cortex and the amygdala, and the hypothalamus carries out the body's response but does not detect the threat itself.
Overactivity of this alarm circuit is thought to contribute to anxiety disorders, and imaging studies show greater amygdala activity in several anxiety-related disorders.
Key facts
- Structure
- an almond-shaped cluster of nerve cells in the temporal lobe, part of the limbic system
- Role
- detects threat and starts the fear and anxiety response
- Pathway
- signals the hypothalamus and brainstem, which switch on the sympathetic fight or flight response
- Regulation
- the prefrontal cortex helps to dampen the response once it has started
- Neighbours
- the hippocampus handles memory and the thalamus relays sensory signals
- Anxiety disorders
- overactivity of this circuit is thought to contribute to them
Exam traps
- The hippocampus does not detect the threat: it is mainly involved in memory and supplies context for a fear, but it does not start the response itself.
- The hypothalamus does not detect the threat, because it carries out the body's stress response and acts on instructions from other structures.
- The prefrontal cortex does not set off the fear, because it helps to regulate and dampen emotional responses by communicating with the amygdala.
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