Canonical Circuits of Auditory Cortex.

Douglas and Martin have proposed that neocortex is composed of repeated units of a basic ‘canonical’ local circuit. They define a canonical structure that can be identified in all cortical areas and in all land-based mammalian species where data area available. One important point to establish is to what extent the canonical circuit from sensory cortex can be generalized. There are a number of features, such as the thalamic projection to layer 4 that may be common. In the visual cortex, the output from a local circuit to subcortical structures, such as the thalamus or superior colliculus, arises principally from the deep layers in all areas. The layer 6 pyramidal neurons provide a feedback to the thalamic relay nuclei, whereas the layer 5 pyramidal neurons project to the pulvinar and motor structures, such as the pons and superior colliculus. A stereotypical projection pattern is also seen for the inter-areal connections and the same neurons whose axons form the local circuits also form the long distance connections between areas. Thus, the local network is embedded in a large-scale cortical network. The project here is to explore to what degree these features are expressed in the auditory system of the mouse.