The mammalian neocortex is the most complex tissue of the central nervous system. It is subdivided into functionally distinct areas tangentially differing in cytoarchitecture and connectivity. Neurons within different areas underlie our most sophisticated cognitive and perceptual abilities and are thus highly specialized for the analysis of sensory inputs or the generation of motor output. For example, layer V neurons form the major connections between the neocortex and the spinal cord. In the visual cortex, layer V neurons project to the superior colliculus, while in the sensorimotor cortex, layer V neurons send their axons to the spinal cord. In both regions, there is a subset of neurons send axons to the contralateral cortex. This mature projection pattern of layer V neurons is achieved by a combination of selective axon segment elimination and collateral stabilization. Little is known about the molecular mechanism of this process. To try to address this issue and to understand the molecular mechanism of cortical area specification, here I propose to identify and characterize genes that are differentially expressed in neurons of the visual cortex versus the sensorimotor cortex. The long term goal is to unravel the molecular mechanism of cortical area specification and the mechanism of axon pathfinding.