Monday, June 15, 2009

Lateral Geniculate Nucleus

The lateral geniculate nucleus (LGN) is a subcortical structure which lies in each cerebral hemisphere. It is the primary processing center for visual information received from the retina of the eye. The lateral geniculate nucleus is located inside the thalamus of the brain and is thus part of the central nervous system. The lateral geniculate nucleus consists of six layers of neurons with each alternating layer receiving inputs from a different eye: 3 layers for the left eye and 3 layers for the right.

The lateral geniculate nucleus receives information directly from the ascending retinal ganglion cells via the optic nerve and from the reticular activating system. Neurons of the lateral geniculate nucleus send their axons through the optic radiations, a pathway directly to the primary visual cortex, also known as the striate cortex. The primary visual cortex surrounds the calcarine fissure, a horizontal fissure in the medial and posterior occipital lobe. In addition, the lateral geniculate nucleus gets many strong feedback connections from the primary visual cortex.

Two types of information: motion vs. color and form, are kept in separate layers in the lateral geniculate nucleus; these being the magnocellular and parvocellular layers, respectively. The lateral geniculate nucleus is innervated by most of the optic tract axons arising from retinal ganglion cells. In turn, neurons in the lateral geniculate nucleus give rise to axons that project by way of the optic radiation to the striate cortex in the ipsilateral occipital lobe.