Striate Cortex

Abstract

The striate cortex is an expanse of cortical tissue that in higher mammals comprises a large portion of the occipital lobe. Transverse sections of this tissue, when stained (e.g., with cresyl violet), reveal a distinct striation in layer 4 of its multiple laminae, called the stripe of Gennary; this stripe is not evident in other cortical areas. Six major laminae have been identified, spanning a thickness of approximately 2 mm of gray matter, which have been further divided into several sublaminae. In primates the striate cortex is the major recipient zone of the input from the dorsal lateral geniculate nucleus of the thalamus; fibers terminate most profusely in layer 4c which has two subdivisions, 4c alpha and 4c beta. In primates the projections to 4c alpha and beta originate from the magnocellular and parvocellular divisions of the lateral geniculate nucleus, respectively, and represent two distinct information processing Channels originating in the retina, which in Old World monkeys have been identified as the color-opponent and broad-band Channels. There are also less dense projections from the lateral geniculate nucleus to layers 1 and 6. The striate cortex makes extensive connections with several extrastriate regions; these projections originate predominantly in layers dorsal to 4c. Projections to subcortical areas, including the thalamus and the midbrain, originate predominantly in layers 5 and 6.