The large numbers of cortical neurons with diverse anatomical and physiological properties form millions of internal connections and also receive information from the outside world and transmit information to other areas of the central nervous system. My research group uses the mouse visual cortex as a representative animal model of the mammalian neocortex. To understand the principles of information transmission and processing in the mouse visual cortex we label functionally characterized cells and their synaptic partners, then we examine their connectivity together with all the other inputs they receive using large-scale three-dimensional reconstruction of the area at electron microscope level. Our result will help us to understand all the connections and circuits within the cortex at a level of a single synapse which later allow us to make a more accurate computational model of the mammalian neocortex, the area associated with the higher functions of our brain such as perception, generating motor command, and conscious thought.