CorpusHuman Anatomy
NervousBrain region

Thalamus

Thalamus

Also known as: dorsal thalamus

A paired egg-shaped mass of nuclei forming most of the diencephalon; the obligatory relay through which almost all sensory, motor and limbic information reaches the cortex, and a regulator of arousal and attention.

Show on body map Brain — Midsagittal Section

Overview

Length≈3 cm
Interthalamic adhesion present≈70–80% of people
Sensory modality that bypasses itOlfaction (initially)

Each thalamus is about 3 cm long. It forms the upper lateral wall of the third ventricle, and the two sides are often joined across the ventricle by the interthalamic adhesion (massa intermedia), present in ≈70–80% of people. Laterally it is bounded by the posterior limb of the internal capsule, and its upper surface forms part of the floor of the lateral ventricle. A Y-shaped sheet of white matter, the internal medullary lamina, divides it into anterior, medial and lateral nuclear groups. The intralaminar nuclei lie within the lamina, and the GABAergic reticular nucleus forms a thin outer shell.

Every sensory pathway except smell relays here before reaching the cortex, and the thalamus also relays motor loops from the cerebellum and basal nuclei. Its connections with the cortex are reciprocal: each relay nucleus receives heavy feedback from the area it projects to. This lets the thalamus gate information depending on attention and state of arousal. Its intralaminar nuclei are part of the ascending arousal system, and thalamocortical oscillations generate sleep spindles and other EEG rhythms.

Location

Dorsal diencephalon, on either side of the third ventricle; lateral boundary = posterior limb of the internal capsule; lies above the hypothalamus (separated by the hypothalamic sulcus).

Parts & subdivisions

  1. Ventral posterolateral nucleus (VPL)
    Somatosensation from the body: receives the medial lemniscus and spinothalamic tract → primary somatosensory cortex (areas 3, 1, 2).
  2. Ventral posteromedial nucleus (VPM)
    Somatosensation from the face (trigeminothalamic tracts) and taste (solitary nucleus) → face area of the postcentral gyrus and the gustatory cortex.
  3. Lateral geniculate nucleus (LGN)
    Vision: optic tract → optic radiation → primary visual cortex. Six layers (magnocellular 1–2, parvocellular 3–6).
  4. Medial geniculate nucleus (MGN)
    Hearing: from the inferior colliculus (brachium) → auditory radiation → primary auditory cortex.
  5. Ventral lateral (VL) and ventral anterior (VA) nuclei
    Motor relay: VL from the cerebellum (dentate) and the basal nuclei → motor and premotor cortex; VA from the basal nuclei → premotor and prefrontal cortex.
  6. Anterior nucleus
    Limbic: mammillothalamic tract → cingulate gyrus (Papez circuit; memory).
  7. Mediodorsal (dorsomedial) nucleus
    Prefrontal cortex and limbic system: executive function, emotion, memory; damaged in Korsakoff syndrome.
  8. Pulvinar
    Large posterior association nucleus linked to parieto-occipital and temporal cortex; visual attention.
  9. Intralaminar nuclei (centromedian)
    Arousal and attention (part of the reticular activating system); striatal connections.
  10. Reticular nucleus
    GABAergic shell that inhibits relay nuclei; gates thalamocortical traffic; generates sleep spindles and absence-seizure spike–wave rhythms. Does not project to the cortex.

Anatomy

Arterial supply

Posterior cerebral artery (thalamoperforating/paramedian, thalamogeniculate, posterior choroidal branches) and posterior communicating artery (tuberothalamic/polar). A single artery of Percheron variant can supply both paramedian thalami.

Function

  • Relay of all sensory modalities except olfaction to the cortex
  • Integration and gating of information according to attention and arousal
  • Motor relay of the cerebellar and basal-nuclei loops to the motor cortex
  • Limbic and memory functions (anterior and mediodorsal nuclei)
  • Regulation of consciousness, sleep and cortical rhythms

Clinical significance

Thalamic stroke and Dejerine–Roussy syndrome

A lacunar infarct of VPL/VPM (thalamogeniculate branch of the PCA) causes pure sensory stroke, i.e. contralateral hemisensory loss of the face, arm and leg. Weeks later severe burning, allodynic central post-stroke ("thalamic") pain may develop. An artery of Percheron occlusion causes bilateral paramedian thalamic infarction with coma or hypersomnolence, vertical gaze palsy and amnesia.

Absence seizures

Rhythmic oscillation between the thalamic reticular nucleus and the cortex, driven by T-type Ca²⁺ channels, generates the 3-Hz spike-and-wave discharge of childhood absence epilepsy. Ethosuximide blocks T-type Ca²⁺ channels.

Mnemonics

Geniculate nuclei

"Lateral = Light (vision); Medial = Music (hearing)."

Ventral posterior nuclei

"VPL = Limbs/body; VPM = Mouth/face (and taste — think make-up on the face)."

Compiled from standard anatomy and physiology references — see the Nervous System sources. For education only; not medical advice.