All parts of the brain › Functions › Thirst

What part of the brain controls thirst?

Mainly the hypothalamus and the thin front wall of the third ventricle, the lamina terminalis. [1][2][3][4]

The 3D brain needs JavaScript. The list of parts still says what each one does for thirst.

Lit: whole parts; region borders not drawn.

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All 6 parts are lit together. Drag to turn, pinch or scroll to zoom, tap a part on the brain or a name in the list to focus it; .

Two small sensing organs there, the organum vasculosum of the lamina terminalis (OVLT) and the subfornical organ, sit outside the blood–brain barrier, so their neurons can read how salty the blood is and how much angiotensin II it carries. They signal the median preoptic nucleus of the hypothalamus, which starts water seeking and drinking, and the hypothalamic neurons that make vasopressin, which the pituitary gland releases. The feeling of thirst itself shows up in the cortex, most consistently in the anterior cingulate and the insula. [1][2][3][4]

The organum vasculosum of the lamina terminalis is a region on the lamina terminalis, not a separate shape. The 3D model has no shape for it, so the whole lamina terminalis is lit; the region’s exact border is not drawn.

The subfornical organ is a region on the fornix, not a separate shape. The 3D model has no shape for it, so the whole fornix is lit; the region’s exact border is not drawn.

The median preoptic nucleus is a region on the hypothalamus, not a separate shape. The 3D model has no shape for it, so the whole hypothalamus is lit; the region’s exact border is not drawn.

Thirst: 6 parts lit

Hypothalamus, lamina terminalis, fornix, pituitary gland, insula and cingulate gyrus. Tap one to see where it is and what it does.

The parts and their roles

Its median preoptic nucleus, at the very front, receives the signals of low blood volume and salty blood from the subfornical organ and OVLT and starts water seeking and drinking; neurons of the lamina terminalis also project to its supraoptic and paraventricular nuclei, which make vasopressin. [1][5][2] Where is the hypothalamus?
The thin sheet that forms the front wall of the third ventricle, stretching from the interventricular foramen down to the base of the optic stalk. It holds the OVLT, one of the brain’s three sensory circumventricular organs: its capillaries have no blood–brain barrier, and its neurons are osmoreceptors that sense the sodium content and osmotic pressure of the blood. [6][2] Where is the lamina terminalis?
The subfornical organ, named for where it sits, lies on the underside of the fornix near the interventricular foramina, where the lateral ventricles open into the third ventricle. Its neurons carry receptors for angiotensin II, the hormone made when blood volume falls, which starts drinking and salt appetite through this organ; some of them are osmoreceptors too. [3][1] Where is the fornix?
Its posterior lobe releases vasopressin (antidiuretic hormone) into the blood: the subfornical organ and OVLT signal the hypothalamus to form it, the pituitary releases it, and it makes the kidneys hold on to water while the blood is too concentrated. [1][7][8] Where is the pituitary gland?
Active as thirst rises: in brain scans of people made thirsty by an infusion of salty water, the insula lit up together with the anterior cingulate, and tracing studies in animals show it receives input from the thirst neurons of the subfornical organ and OVLT. [9][4][10] Where is the insula?
Its front part, the anterior cingulate cortex (Brodmann area 32), is the area most tied to being aware of thirst: its signal was strong as thirst entered awareness and fell steeply as soon as people drank to satiation. [4][9] Where is the cingulate gyrus?

Named areas on the lit gyri

The organum vasculosum of the lamina terminalis, on the : Also called the OVLT, the vascular organ of the lamina terminalis or the supraoptic crest: a sensory circumventricular organ of the third ventricle, within the lamina terminalis, covered with pia mater and lined with ependyma. With the subfornical organ and the median preoptic nucleus it forms the region in front of and below the third ventricle (AV3V) that controls thirst, sodium excretion and vasopressin secretion. [2][3]
The subfornical organ, on the : One of the circumventricular organs, on the ventral (under) surface of the fornix near the interventricular foramina; it is well supplied with capillaries, some of them leaky (fenestrated), and is classed as a sensory organ because it responds to many hormones carried in the blood. [3]
The median preoptic nucleus, on the : Also called the nucleus medianus: the uppermost of the four nuclei of the preoptic area, at the front of the hypothalamus, wired to the subfornical organ and OVLT; besides thirst and drinking it takes part in sleep and in body temperature. [5][3]

How they work together

There are two kinds of thirst. Osmometric (intracellular) thirst comes when the fluid around the cells gets saltier, for example after a salty meal or water lost in sweat, so water is drawn out of the cells and osmoreceptors in the OVLT and subfornical organ fire. Volume (extracellular) thirst comes when blood volume falls: cells in the kidneys release renin, which leads to angiotensin II in the blood, and angiotensin II starts drinking and salt appetite through the subfornical organ. [1]
These two organs can read the blood because they are circumventricular organs: their capillaries are fenestrated and lack the blood–brain barrier that keeps most of the brain sealed off, so their neurons respond to substances circulating in the body. The third sensory organ of this kind, the area postrema, sits in the medulla. [3][2]
The signal runs inward: the area postrema and the nucleus of the solitary tract in the medulla (carrying blood-pressure and blood-volume news from the heart and arteries) signal the subfornical organ and the lateral parabrachial nucleus, which relays on to the median preoptic nucleus; from there the signals reach the areas of the forebrain cortex where thirst is felt. [1]
Drinking switches thirst off before the water has reached the blood. In Egan’s scans, thirst ratings fell to baseline at once and the anterior cingulate signal dropped steeply, while the wall of the third ventricle stayed just as active, because 15–20 minutes are needed before water absorbed from the gut changes the blood’s sodium. Signals from the mouth, throat, oesophagus and stomach anticipate how much has been drunk. [4][1]
The sense of thirst weakens with age: in adults over 50 it is reduced and keeps falling, and in a PET study older men made thirsty by the same salty infusion drank about half as much water as younger men (1.9 versus 3.9 ml per kg). [1][11]
An honest limit: the OVLT, the subfornical organ and the median preoptic nucleus are each a small cluster of cells, too small for this atlas, so the lamina terminalis, fornix and hypothalamus that hold them are lit whole and no marker is guessed. The cortical parts come from brain scans of small groups (Egan’s study scanned 10 people with PET and 4 with fMRI); they show which areas are active during thirst, not that those areas alone make the feeling. [4][10]

Vasopressin, the water-keeping hormone the thirst sensors call for, is one of the two hormones that hypothalamic neurons make and the posterior pituitary stores and releases. [8][7] What part of the brain controls hormones?

Sources

Facts describe anatomy and normal function only. A part lit here takes part in thirst; it does not do it alone, and it does other jobs too. The 3D model is the adult male BodyParts3D brain (credits and licence); on it the brainstem includes the midbrain, pons and medulla, so lighting the brainstem lights all three.