Feedforward, feedback and inhibitory connections in primate visual cortex.

Visual cortical circuits are organized at multiple levels of complexity including cortical areas, layers and columns, and specific cell types within these modules. Making sense of the functions of these circuits from anatomical observations requires linking these circuits to function at each of these levels of complexity. Observations of these relationships have become increasingly sophisticated over the last several decades, beginning with correlations between the connectivities and functions of various visual cortical areas and progressing toward cell type-specificity. These studies have informed current views about the functional interactions between cortical areas and modules and the mechanisms by which fine scale microcircuits influence interactions at more coarse levels of organization.