Cuneus

At a glance

English

Cuneus

Latin (TA2)

Cuneus

System

Brain and spinal cord

Region

Head

Side

Paired, left and right

About the cuneus

The cuneus (Latin for a wedge) is a triangular piece of cortex on the inner, medial face of the occipital lobe. Its front border is the parieto-occipital sulcus, which separates it from the precuneus of the parietal lobe; its lower border is the calcarine sulcus, below which lies the lingual gyrus. The two sulci meet in front to form the narrow tip of the wedge, while its broad base lies along the upper margin of the hemisphere towards the occipital pole.

The upper lip of the calcarine sulcus, which forms the lower edge of the cuneus, belongs to the primary visual cortex (striate cortex, Brodmann area 17). This cortex receives the optic radiation from the lateral geniculate body. The fibres that reach the cuneus come from the upper half of the retina of each eye on the same side and therefore carry the lower quarter of the opposite half of the visual field. The rest of the cuneus is visual association cortex, Brodmann areas 18 and 19, to which the striate cortex sends its output.

It is chiefly concerned with early stages of vision: detecting edges, orientation, contrast and simple motion, and passing these signals forward into the dorsal and ventral visual streams. Activity in the extrastriate parts of the cuneus is adjusted by attention, working memory and the expectation of reward, so it is not a purely passive relay. Imaging studies have linked its grey matter with impulse control in some psychiatric conditions and have shown greater activity in people with gambling problems, but these findings are of research interest rather than diagnostic use.

Damage to the cuneus of one side, typically from an infarct of a calcarine or parieto-occipital branch of the posterior cerebral artery, produces a quadrant of blindness in the lower part of the opposite visual field (an inferior quadrantanopia), often with sparing of central vision because the occipital pole may receive extra supply. Damage on both sides causes loss of the lower field in both eyes.

Function and supply

Function

Part of the visual cortex: its lower edge receives the upper retina (the opposite lower visual field), and the rest processes early visual features for the visual streams.

Blood supply

Calcarine and parieto-occipital branches of the posterior cerebral artery.