Cortical Circuits

The local circuits in the neocortex of mammals consists of neurons that need to obtain reliably meaningful information from their dominant activating inputs and to alter their responses to these inputs in relation to inputs that are activating other local cortical circuits. Both of these tasks are mediated by structural features in the neocortex. This chapter discusses the structural features of mammalian neocortex as well as the features that allow dynamic interaction among neurons in different columns. The focus is on the complex variability within and across nervous systems involving neuron densities and proportions to glia and other nonneural cells. The chapter also looks at dendritic arbors of cortical pyramidal cells and how they vary across cortical areas and species, patterns of intrinsic horizontal areal connections, and feedback connections from higher to lower areas in hierarchies of cortical areas.