Side by side
| Compared | Amygdala | Hypothalamus |
|---|---|---|
| Where it is | Deep in the medial temporal lobe of each hemisphere, just in front of the hippocampus; there are two, one on each side. [1] | On the midline at the base of the brain, below the thalamus, forming the floor and lower walls of the third ventricle; the pituitary gland hangs from it on a stalk. [2] |
| What it does | Processes the emotional significance of what is sensed, especially threat and fear, and strengthens memories of emotional events; it also takes part in reward and decision-making. [1] | Controls body temperature, hunger, thirst, fatigue and sleep and circadian rhythms, and links the nervous system to the hormone system through the pituitary gland. [2] |
| Connects with | The stria terminalis and the ventral amygdalofugal pathway carry its output to the hypothalamus and the brainstem; it trades signals with the hippocampus and the prefrontal cortex. [1][4] | Its neurons send releasing hormones down the portal veins of the pituitary stalk to the anterior pituitary and their own axons into the posterior pituitary; the fornix brings it input from the hippocampus at the mammillary bodies. [2][5][6] |
| Size measured from the model | 18 mm front to back, 13 mm top to bottom, 17 mm side to side [3] | 18 mm front to back, 20 mm top to bottom, 17 mm side to side [3] |
Size is the box each part fits in on this one model (left amygdala; hypothalamus), not its volume. Real brains vary. A part that comes as a left and a right copy is measured on its left copy; the right one mirrors it.
How far apart are they?
Measured from the model [3], from the left amygdala to the hypothalamus:
- Centre to centre: 26 mm in a straight line.
- The centre of the hypothalamus is 1 mm further forward, 3 mm higher and 26 mm closer to the midline than the centre of the left amygdala.
- Nearest points of the two shapes: about 9 mm apart.
A “centre” here is the average position of the points on the part’s 3D surface, so for a curved part such as a C shape it can sit outside the part itself. The nearest-points figure is measured between the corners of the simplified meshes, so a gap of 2 or 3 mm or less is within the model’s coarseness: read it as “touching or nearly so”.
How to tell them apart
- One is paired and one is not: there are two amygdalae, one in each temporal lobe, but a single hypothalamus on the midline between and above them. [1][2]
- They are wired together: the stria terminalis, a thin bundle that curves round the lateral ventricle beside the caudate nucleus, carries signals from the amygdala to the hypothalamus. [4]