Figure 1. A) Photograph of an unstained coronal block, containing the prefrontal cortex, cut immediately anterior to the corpus callosum through the left hemisphere of a postmortem human brain. This block also includes the adjacent anterior cingulate gyrus (ACG) of the limbic lobe. The portion of the dorsolateral prefrontal cortex (DLFPC) delineated by the small rectangle is shown at higher magnification in panel B. B) Nissl-stained section showing the typical appearance of six layers or lamina, numbered from the pial surface of the cortex to the underlying white matter, based on the size and packing density of neurons. C) Schematic representation of neurons across cortical layers. Pyramidal neurons (red) represent about 75% of cortical neurons and typically have triangularly-shaped cell bodies, a single apical dendrite directed towards the pial surface, and an array of basilar dendrites. Depending on their laminar location, the axons of pyramidal neurons preferentially provide excitatory projections to different brain regions. Axons that project to the DLPFC from other brain regions also tend to innervate different subsets of cortical layers. For example, axonal projections (green) from the thalamus terminate in layers deep 3 and 4. The remaining -25% of DLPFC neurons are local circuit or interneurons (blue). These neurons use the inhibitory neurotransmitter GABA, and have axons that arborize locally and innervate other neurons in the same area of the prefrontal cortex. Reproduced from ref 1: Lewis DA, Gonzalez-Burgos G. Neuroplasticity of neocortical circuits in schizophrenia. Neuropsychopharmacology. 2008;33:141-165. Copyright©Nature Publishing Group 2008.