Thalamus

At a glance

English

Thalamus

Latin (TA2)

Thalamus

System

Brain and spinal cord

Region

Head

Side

Paired, left and right

About the thalamus

The thalamus, from the Greek for inner chamber, is the largest part of the diencephalon. Each is an egg-shaped mass lying deep in the brain above the midbrain and on either side of the third ventricle. Its medial surface forms the upper part of the ventricle's lateral wall and is often joined to its partner across the ventricle by a small grey bridge, the interthalamic adhesion. Its upper surface forms part of the floor of the lateral ventricle, separated from the caudate nucleus by the stria terminalis and thalamostriate vein; its lateral surface rests against the internal capsule. The narrow front end bears the anterior tubercle, and the broad back end, the pulvinar, overhangs the midbrain; beneath it sit the medial and lateral geniculate bodies.

Thin layers of white matter divide it. A stratum zonale covers its upper surface, an external medullary lamina covers its lateral surface, and a Y-shaped internal medullary lamina splits it into anterior, medial and lateral nuclear groups. The thin reticular nucleus forms a shell on its outer side. The lateral group includes the ventral anterior, ventral lateral and ventral posterior nuclei, the pulvinar and the geniculate bodies, which together make up its most recently evolved part.

Almost every pathway to the cortex passes through the thalamus. Each sense apart from smell has its own relay: the ventral posterior nuclei for touch, pain and position sense from the body and face, the lateral geniculate body for vision and the medial geniculate body for hearing. The ventral anterior and ventral lateral nuclei carry signals to the motor cortex from the cerebellum and basal ganglia. The anterior nuclei, fed by the mammillothalamic tract, belong to the memory circuit, and the mediodorsal nucleus links with the prefrontal cortex. Two-way loops with the cortex through the thalamic radiations mean it does more than pass signals on: it filters and shapes them and helps control sleep, wakefulness and alertness.

Strokes in the thalamus can cause loss of sensation on the opposite side, sometimes followed by a severe burning thalamic pain. Blockage of a single artery of Percheron, a variant supplying both sides, can damage both thalami at once and cause drowsiness or coma with eye movement problems. Thalamic damage also contributes to the memory loss of Korsakoff syndrome.

Function and supply

Function

Relays and filters sensory, motor and limbic signals on their way to the cortex, with the exception of smell, and helps regulate consciousness, sleep and alertness.

Blood supply

Branches of the posterior cerebral and posterior communicating arteries: the polar (tuberothalamic), paramedian, thalamogeniculate and posterior choroidal arteries.