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.
The cerebral cortex consists of folded bulges called gyri that create deep furrows or fissures called sulci. 1  The folds in the brain add to its surface area and therefore increase the amount of gray matter and the quantity of information that can be processed.