lgn

The lateral geniculate nucleus (LGN) is a paired thalamic relay center in the visual pathway, located in the dorsal thalamus on each side of the brain. It receives input from retinal ganglion cells via the optic tract and projects to the primary visual cortex, forming a key stage between the retina and cortical processing.

In primates, the LGN comprises six principal layers in each hemisphere: magnocellular layers I and II, parvocellular layers III through VI, and intercalated koniocellular (K) layers that lie between the main layers. Magnocellular layers respond to luminance contrast and motion with high temporal resolution, while parvocellular layers are sensitive to color and high-acuity form with high spatial resolution. Koniocellular layers contribute to additional color processing, particularly blue–yellow signals. The layers receive input predominantly from the contralateral eye, and the LGN exhibits a retinotopic map so adjacent cells correspond to neighboring regions of the visual field.

Connections and function: Retinal input travels to the LGN via the optic tract, and the LGN relays information to the primary visual cortex (V1, striate cortex) through the optic radiations, targeting the thalamic inputs to cortical layer IV. The LGN maintains parallel processing streams across its layers, supporting motion, color, and form information before cortical interpretation.

Clinical notes: Lesions in the LGN can cause contralateral visual field defects, with the exact pattern depending on which layers or regions are affected. The LGN also has extensive reciprocal connections with V1 and with higher-order visual areas, reinforcing its role as an early, organized relay in the visual system.