Circuits of Neocortex
Our every thought, every idea, every memory, every decision, and every action, depends on the activity coursing through the highly structured circuits of our nervous system. Of all brain regions, the neocortex, which forms over 80% of the volume of the human brain, has been the most critical for our evolution as humans. But there is a paradox: the basic local architecture and circuits of the human neocortex appear to be very similar to that of a mouse, and indeed very similar to the neocortex of all land mammals. To see to what degree this similarity exists, we mapped the wiring of local circuits and their connections in various species, including primates, and studied their functional properties by experiment and computer simulations. Our conclusions are summarised in our ‘canonical circuit for neocortex’, which provides a powerful means of connecting different levels of analysis, from synapses to cognition, and forms a significant step to unravel the paradox.
Canonical circuit in the cat’s visual cortex. A reconstructed a single pyramidal cell of layer 6 (dendrites red, axon blue) is superimposed on a Nissl-stained transverse section showing the 6 layers of the cat’s visual cortex. The black box diagram is one end-point of our comprehensive quantitative estimate of the proportion (%) of synapses provided by different neuronal types in the different layers. This diagram shows only the excitatory populations. (Montage courtesy Tom Binzegger)