The map of functional cortical areas, which include primary motor and visual cortex, originates from a 'protomap', which is regulated by molecular signals such as fibroblast growth factor FGF8 early in embryonic development. These signals regulate the size, shape, and position of cortical areas on the surface of the cortical primordium, in part by regulating gradients of transcription factor expression, through a process called cortical patterning. Examples of such transcription factors include the genes EMX2 and PAX6. Together, both transcription factors form an opposing gradient of expression. Pax6 is highly expressed at the rostral lateral pole, while Emx2 is highly expressed in the caudomedial pole. The establishment of this gradient is important for proper development. For example, mutations in Pax6 can cause expression levels of Emx2 to expand out of its normal expression domain, which would ultimately lead to an expansion of the areas normally derived from the caudal medial cortex, such as the visual cortex. On the contrary, if mutations in Emx2 occur, it can cause the Pax6-expressing domain to expand and result in the frontal and motor cortical regions enlarging. Therefore, researchers believe that similar gradients and signaling centers next to the cortex could contribute to the regional expression of these transcription factors.