Cytology of human caudomedial cingulate, retrosplenial, and caudal parahippocampal cortices

Brodmann showed areas 26, 29, 30, 23, and 31 on the human posterior cingula te gyrus without marking sulcal areas. Histologic studies of retrosplenial areas 29 and 30 identify them on the ventral bank of the cingulate gyrus (C Gv), whereas standardized atlases show area 30 on the surface of the caudom edial region. This study evaluates all areas on the CGv and caudomedial reg ion with rigorous cytologic criteria in coronal and oblique sections Nissl stained or immunoreacted for neuron-specific nuclear binding protein and no nphosphorylated neurofilament proteins (NFP-ir). Ectosplenial area 26 has a granular layer with few large pyramidal neurons below. Lateral area 29 (29 1) has a dense granular layer II-IV and undifferentiated layers V and VI. M edial area 29 (29m) has a layer III of medium and NFP-ir pyramids and a lay er IV with some large, NFP-ir pyramidal neurons that distinguish it from ar eas 291, 30, and 27. Although area 29m is primarily on the CGv, a terminal branch can extend onto the caudomedial lobule. Area 30 is dysgranular with a variable thickness layer IV that is interrupted by large NFP-ir neurons i n layers IIIc and Va. Although area 30 does not appear on the surface of th e caudomedial lobule, a terminal branch can form less that 1% of this gyrus . Area 23a is isocortex with a clear layer IV and large, NFP-ir neurons in layers IIIc and Va. Area 23b is similar to area 23a but with a thicker laye r IV, more large neurons in layer Va, and a higher density of NFP-ir neuron s in layer III. The caudomedial gyral surface is composed of areas 23a and 23b and a caudal extension of area 31. Although posterior area 27 and the p arasubiculum are similar to rostral levels, posterior area 36' differs from rostral area 36. Subregional flat maps show that retrosplenial cortex is o n the CGv, most of the surface of caudomedial cortex is areas 23a, 23b, and 31, and the retrosplenial/parahippocampal border is at the ventral edge of the splenium. Thus, Brodmann's map understates the rostral extent of retro splenial cortex, overstates its caudoventral extent, and abridges the caudo medial extent of area 23. J. Comp. Neurol. 438:353-376, 2001. (C) 2001 Wile y-Liss, Inc.