The PFC was originally termed the “frontal granular cortex” based upon the presence of a cortical granular layer IV and a location rostral to the agranular premotor cortex. However, subsequent comparisons across species of other cortical areas with known functional homology soon revealed that defining cortical regions based upon a granular versus agranular cytoarchitecture was invalid, and current definitions of the PFC utilize functional homology and anatomical connectivity across species. With regard to connectivity, the presence of dense reciprocal projections between the mediodorsal nucleus of the thalamus along with certain cortico-cortical connections is now considered the major defining structural feature of the PFC that is applicable to all mammalian species (Fuster, 2008).
