The amygdala explained, with a 3D model of the limbic system

First written in 2019. Rewritten in November 2026.

The amygdala is the part of the brain that reacts before you have time to think. It is at the heart of a fright, a flaring temper and the feeling an old memory carries. It sits inside a group of structures called the limbic system, and the easiest way I know to understand it is to look at a model.

This is a full-colour 3D model of the limbic system. Each colour is a different part. Below, I explain the amygdala first, then every numbered part of the model, then how they work together when something frightens you.

The limbic system: where the amygdala lives

The limbic system sits deep in the middle of the brain, beneath the thinking brain (the cortex) and wrapped around the top of the brainstem. Older textbooks call it the mammalian brain, which is the title on my guide at the foot of this page.

At its centre is the thalamus, and almost everything you see, hear, taste and touch passes through it on the way in. It is where emotional responses start and where memories are made and filed, and it has a strong hand on the nervous system and the body’s hormones.

The amygdala

There are two of them, one on each side of the brain, deep inside the temporal lobes. The name comes from the Greek for almond, which is roughly its shape and size. On the model it is number 3: the rounded knob at the front end of the lower curl.

It has four jobs worth knowing.

1. The alarm

The amygdala checks everything that comes in for danger, and it does it fast. Signals from the senses reach it by a short route straight from the thalamus, as well as by a longer route through the thinking brain. The short route is quicker and rougher. So the amygdala can set off a reaction before you know what you are reacting to: you jump back from a shape in the grass, and only a moment later see that it is a stick, not a snake. The neuroscientist Joseph LeDoux, who mapped these two routes in rats, called them the low road and the high road. How much the short route matters in people is still debated.

2. The trigger for freeze, fight or flight

When the amygdala judges something a threat, it signals the hypothalamus (number 2), which sets the body going. The nervous system releases adrenaline within moments, and the pituitary gland starts a slower chain that ends in cortisol, the stress hormone. Your heart rate rises, your breathing quickens, your muscles tighten and digestion pauses. You freeze, fight or run before you have decided to.

If you have a temper, this is the button people often press.

3. The keeper of emotional memory

Put simply, the hippocampus (number 4) records what happened and the amygdala records how it felt. That is why frightening or painful moments are remembered so sharply, and why the feeling can come back before the memory does: a smell, a tone of voice or a face can set the alarm off again without your knowing why.

4. More than fear

The amygdala is best known for fear, but it responds to anything that matters to us, good or bad: a familiar face, a reward, something new. Its job is to flag what needs attention.

Why it can feel as if it takes over

The amygdala is fast. The thinking brain at the front, the prefrontal cortex, is slower, but it can calm the amygdala down. Most of the time the two work together. Under pressure, the fast one can get there first and run the show for a while. The psychologist Daniel Goleman called this an amygdala hijack.

That is one reason a pause, a slow breath or putting a name to what you feel can help: each gives the slower brain a chance to catch up. In one brain-scan study, simply naming a feeling quietened the amygdala. And because the amygdala learns, its reactions can be relearned. Neurons that fire together wire together; I wrote about that in Smiling and Hebb’s Law.

One 2019 study suggests part of the amygdala may never fully grow up: a group of nerve cells, many of which mature in the teenage years, while some stay immature into adult life. I wrote about what that might mean in Have scientists found the inner child?

The model, part by part

The numbers match the photos above and the guide at the foot of this page.

1. Thalamus. The relay station: the large blue part at the centre. Sight, sound, taste and touch pass through it on their way to the rest of the brain. Smell is the exception; it takes a more direct route, although my guide lists it here.
2. Hypothalamus. A small region just below the thalamus. It controls the pituitary gland, and through it much of the body’s hormone system. It also governs body temperature, hunger, thirst and sleep, and it starts the stress response.
3. Amygdala. Emotional memory and the freeze, fight or flight trigger, as above.
4. Hippocampus. The flat orange strip low down. It holds episodic memory, what happened, where and when, and decides what to keep and how to find it again. It is also one of the few places in the brain where new nerve cells have been found forming; how far that continues into adult life is still argued over.
5. Hippocampal gyrus. Also called the parahippocampal gyrus: the pale base the hippocampus rests on. It helps store and recall memories, especially of places and scenes.
6. Fornix. The dark arch that curls around the thalamus. It is a bundle of nerve fibres carrying signals from the hippocampus forward to the mammillary bodies and the hypothalamus. A similar curved bundle, the stria terminalis, runs from the amygdala to the hypothalamus. It is one of the main routes by which a fright can turn into a surge of hormones almost at once. (My guide, made in 2019, gives this wiring to the fornix; it belongs to the stria terminalis.)
7. Corpus callosum. The thick yellow arch: the great bundle of nerve fibres that joins the left and right halves of the brain so they work as one. Strictly it is not part of the limbic system, but it frames it. My guide calls the left half logic and the right half creative; that is popular shorthand. Each half does some things better, but no one is simply left-brained or right-brained.
8. Cingulate gyrus. The crinkled crimson band across the top. It is a fold of cortex that links the emotional brain below with the thinking brain above. It helps us notice emotion, pain and mistakes, and steer how we respond to them.
9. Mammillary bodies. Two small round bumps on the underside, green on the model. They are part of the hypothalamus and a relay for memory, including memory of where things are.
10. Pineal gland. A tiny gland towards the back that releases melatonin, the hormone that tells the body it is time to sleep. Like the corpus callosum, it sits beside the limbic system rather than in it.

How it works together: a fright, step by step

1. Something reaches your senses. The signal goes to the thalamus (1).
2. The thalamus sends a quick, rough copy to the amygdala (3) and a slower, fuller copy to the thinking brain.
3. The amygdala flags a threat and signals the hypothalamus (2).
4. The hypothalamus sets off adrenaline straight away and, more slowly, through the pituitary gland, cortisol. Your heart races and your body gets ready to freeze, fight or run.
5. The hippocampus (4) records what happened; the amygdala records how it felt. Next time, a smaller cue can set the alarm off.
6. The thinking brain catches up, with help from the cingulate gyrus (8), and can say: it’s a stick, not a snake. The alarm settles.

Why it matters

When someone says “I don’t know why I reacted like that”, the honest answer is often that the amygdala reacted before they had a chance to think. That reaction is fast, physical and often learned. It is not a failing of character. And what is learned can, with time, be relearned.

To see where the limbic system fits in the bigger picture of how we act and react, read Human behaviour explained.

The guide

Save this image to keep the labelled key.

To read more about behaviour, neurology and psychology, see my essays.