The relay station through which all senses except smell are routed to the cortex
Thalamus — the great sensory gateway.
Anatomy · Brain & nerves
Thalamus
Greek 'inner chamber'
Brain · diencephalon
Two egg-shaped masses of grey matter, one on each side of the third ventricle, deep in the centre of the brain above the brainstem. Nearly all sensory information — sight, hearing, touch, taste, pain — passes through it on its way to the cerebral cortex, so it is often called the brain's relay station; only smell bypasses it. It also takes part in motor control, sleep and consciousness.
How to spot them
- ▸A pair of smooth, egg-shaped grey masses flanking the slit-like third ventricle, roughly 3 cm long
- ▸Often joined across the midline by a small bridge of grey matter, the interthalamic adhesion
- ▸Sits above the stalk of the brainstem and below the lateral ventricles; a band of white matter (the internal capsule) lies to its outer side
- ▸On the back, a pillow-like swelling called the pulvinar overhangs the midbrain
What to know
Two egg-shaped masses on either side of the slit-like third ventricle, often joined by a small grey bridge
Thalamus — the bridge is the interthalamic adhesion (massa intermedia).
Its Greek name means 'inner chamber' or 'bedroom'
Thalamus — from the Greek thalamos.
Contains the lateral geniculate body, a relay for vision, and the medial geniculate body, a relay for hearing
Thalamus — the geniculate nuclei.
Stroke here can cause a severe burning pain on the opposite side of the body, named after two French neurologists
Thalamus — Dejerine–Roussy (thalamic pain) syndrome.
Progressive loss of its nuclei in a rare inherited prion disease produces untreatable insomnia
Thalamus — fatal familial insomnia.
Forms the largest part of the diencephalon, sitting directly above the structure that controls the pituitary
Thalamus — the diencephalon also includes the hypothalamus, epithalamus and subthalamus.
Key ideas
- Each sensory route has its own thalamic nucleus: ventral posterior nuclei for touch and pain, lateral geniculate for vision, medial geniculate for hearing.
- The relay is two-way: the cortex sends fibres back to the nuclei that feed it, so it filters as well as passes on.
Quick-fire facts
- •Two egg-shaped masses, about 3 cm long, either side of the third ventricle, forming most of the diencephalon
- •All senses except olfaction synapse in it before reaching the cortex
- •The interthalamic adhesion joins the two halves in most, but not all, people
- •The lateral geniculate nucleus relays visual information from the optic tract, and the medial geniculate relays hearing
- •The internal capsule lies on its outer side, separating it from the basal ganglia
- •Its name is from the Greek thalamos, 'inner chamber'
- •Dejerine–Roussy syndrome follows a stroke in the posterior thalamus, with severe pain on the opposite side
- •Fatal familial insomnia, a prion disease, is characterised by thalamic degeneration
- •Deep brain stimulation of its ventral intermediate nucleus is used to treat severe tremor
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