The term area 23a (macaque) refers to a portion of the posterior cingulate gyrus defined on the basis of cytoarchitecture and connectivity in the macaque ( Vogt-1987 ). It is one of three subdivisions of area 23 (macaque) The other two are area 23b (macaque) and area 23c (macaque). Area 23a lies closest to the corpus callosum. An equivalent area exists in the human ( Vogt-1995 ). For a more recent segmentation of this area reported by the same authors later in their studies ( Vogt-2012 ) see area 23.