Lateral geniculate body

At a glance

English

Lateral geniculate body

Latin (TA2)

Corpus geniculatum laterale

System

Brain and spinal cord

Region

Head

Side

Paired, left and right

About the lateral geniculate body

The lateral geniculate body is the thalamic relay of the visual pathway. It forms a small oval bump on the underside of the back of the thalamus, below the pulvinar and lateral to the medial geniculate body, and receives the end of the optic tract. Its name comes from the Latin genu, a knee, because the grey matter inside it is bent. Within it lies the lateral geniculate nucleus, strictly its dorsal nucleus in human anatomy.

In humans the nucleus is built of six layers of cells, numbered from the inside (ventral) outwards, separated by sheets of optic fibres. The two innermost, 1 and 2, are magnocellular, made of large cells that respond quickly to movement and contrast but not to colour. Layers 3 to 6 are parvocellular, made of smaller cells concerned with fine detail and colour. Thin koniocellular layers lie below each main layer and form a third channel, involved partly in colour. Each layer receives from one eye only: the opposite eye feeds layers 1, 4 and 6, and the same-side eye layers 2, 3 and 5.

Because nasal retinal fibres cross in the optic chiasm while temporal fibres do not, each lateral geniculate body receives from both eyes but deals only with the opposite half of the visual field. Its cells project through the optic radiation, which leaves by the retrolenticular part of the internal capsule, sweeps round the lateral ventricle (the lower fibres looping forwards into the temporal lobe as Meyer's loop) and ends in layer 4 of the primary visual cortex around the calcarine sulcus. The retina provides only a small share of its input; most comes back from the visual cortex itself, from the thalamic reticular nucleus and from brainstem centres. This lets it act as a gate that adjusts what passes on, sharpening timing and helping focus attention on important parts of the scene.

A lesion of one lateral geniculate body, from a stroke of the anterior or lateral posterior choroidal arteries, a tumour or demyelination, causes a homonymous hemianopia, loss of the same half of the visual field in both eyes; because of its dual blood supply, partial wedge-shaped defects are characteristic. The pupil reflex is spared, since pupillary fibres leave the optic tract before it reaches the nucleus.

Function and supply

Function

Relays and filters visual information from the retina of both eyes for the opposite visual field, sending it through the optic radiation to the primary visual cortex.

Blood supply

Anterior choroidal artery (from the internal carotid) and lateral posterior choroidal branches of the posterior cerebral artery.