Layers four and six (4 & 6) of the LGN also connect to the opposite eye, but to the P cells (color and edges) of the optic nerve. By contrast, layers two, three and five (2, 3, & 5) of the LGN connect to the M cells and P (parvocellular) cells of the optic nerve for the same side of the brain as its respective LGN.
A gyrus (gyri pl) is a rounded ridge, as on the surfaces of the cerebral hemispheres. A sulcus is a groove in the surface between gyri.
For the journal of a similar name, see Cortex (journal). The cerebral cortex is a brain structure in vertebrates, including humans. It is the outermost layer of the cerebrum and has a grey color.(Hence the name grey matter.n the higher animals (especially the higher mammals), the surface of the cerebral cortex becomes folded. This creates grooves on the surface of the brain called  sulci  (singular = sulcus). The bumps or ridges on the surface of the brain are called gyri (singular = gyrus).