Fig. 3 Cytoarchitectonic subdivisions of human and monkey cingulate cortex.
A: Along a rostrocaudal axis, the cingulate cortex can be divided into (1) a posterior region (areas 23, 26, 29, 30, 31) characterized mostly by a granular type of cortex and (2) an anterior agranular region (areas 24, 25, 32, 33). The anterior cingulate cortex is an agranular type of cortex (i.e., layer IV is absent) with a prominent and deeply stained layer V. Area 32 has an incipient granular layer IV. A ventrodorsal distinction, based on the degree of laminar differentiation, sets apart the old periallocortical areas adjacent to the corpus callosum (area 33) from the proisocortical region (areas 24, 25) and the paralimbic region on the upper bank of the cingulate sulcus and in the paracingulate gyrus (area 32). In addition to these main rostrocaudal and ventrodorsal distinctions, subtle variations in cytoarchitecture define further subdivisions of area 32, often reflecting structural features of the adjacent neocortical areas. (86) The approximate position of the corticospinal fields is indicated relative to the vertical plane passing through the anterior commissure (VCA). VCP = vertical plane passing through the posterior commissure.
B: Cytoarchitectonic areas superimposed on the flat map of the medial wall of the human brain. The bold lines outline the cingulate region, the thinner dashed lines show the borders between the cingulate areas (e.g., between areas 24 and 23), and the dotted lines indicate the borders between subdivisions of each area (e.g., between areas 24b and 24c). C: Location of the motor areas on the medial wall of the monkey brain. The dotted lines show the boundaries of the cytoarchitectonic areas. Shaded areas correspond to the territory of origin of corticospinal projections to cervical and upper thoracic segments. M1 = primary motor cortex, SMA = supplementary motor area, CMAr = rostral cingulate motor area, CMAd = caudal cingulate motor area, dorsal bank, CMAv = caudal cingulate motor area, ventral bank. Reproduced with permission from Macmillan Magazines Ltd. (www.nature.com/reviews) (Nat Rev Neurosci 2001;2:417–24). (81)