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

Abstract

Brodmann showed areas 26, 29, 30, 23, and 31 on the human posterior cingulate gyrus without marking sulcal areas. Histologic studies of retrosplenial areas 29 and 30 identify them on the ventral bank of the cingulate gyrus (CGv), whereas standardized atlases show area 30 on the surface of the caudomedial region. This study evaluates all areas on the CGv and caudomedial region with rigorous cytologic criteria in coronal and oblique sections Nissl stained or immunoreacted for neuron-specific nuclear binding protein and nonphosphorylated neurofilament proteins (NFP-ir). Ectosplenial area 26 has a granular layer with few large pyramidal neurons below. Lateral area 29 (29l) has a dense granular layer II-IV and undifferentiated layers V and VI. Medial area 29 (29m) has a layer III of medium and NFP-ir pyramids and a layer IV with some large, NFP-ir pyramidal neurons that distinguish it from areas 29l, 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 in layers IIIc and Va. Although area 30 does not appear on the surface of the 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 layer IV, more large neurons in layer Va, and a higher density of NFP-ir neurons 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 parasubiculum are similar to rostral levels, posterior area 36' differs from rostral area 36. Subregional flat maps show that retrosplenial cortex is on 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 retrosplenial cortex, overstates its caudoventral extent, and abridges the caudomedial extent of area 23.

Cytology and functionally correlated circuits of human posterior cingulate areas

“…Retrosplenial cortex is comprised of areas 29 and 30 and these areas are located on the ventral bank of the cingulate gyrus in the callosal sulcus and form transitional structures between the allocortical area 26 and isocortical area 23a (Braak, 1979;Vogt et al, 2001;Zilles, 2004). Although Brodmann placed RSC on the caudomedial lobule, he was using a convoluted brain to plot the areas.…”

“…Since about 50% of PCC is in the callosal, cingulate, and splenial sulci, it was not possible for him to accurately show the topographical limits of cortical areas in sulci without flattening. His placing RSC on the surface of the caudomedial lobule instead of in the callosal sulcus, led to the incorrect extrapolation by Talairach and Tournoux (1988) and other standardized atlases of RSC to the surface of the posterior cingulate gyrus and the result is a conflicting body of work about the functions of areas 23/31 and 29/30 (Vogt et al, 2000(Vogt et al, , 2001. Designation of cingulate areas at x= +/− 14 and y= −50 to −60 as RSC continues because atlases refer to this as area 30 in parasagittal sections and in coronal sections at y= −55 to −60 it is labeled area 31.…”

“…The caudomedial subregion is located on the ventral bank of the cingulate gyrus (Vogt et al, 2001(Vogt et al, , 2004 and has direct projections to subgenual ACC; connections that dorsal PCC and posterior MCC do not have (Vogt and Pandya, 1987). Furthermore, Shibata and Yukie (2003) reported that the dorsal and ventral parts of PCC have unique thalamic connections with the dPCC receiving inputs from the central latocellular, mediodorsal, and ventral anterior and ventral lateral nuclei that do not project to the vPCC.…”

The Economo-Koskinas Atlas Revisited: Cytoarchitectonics and Functional Context

“…Brodmann areas 29 and 30 on the gyral surface. Because the architecture of each cortical area cannot be determined with current imaging modalities, it is imperative that standardized atlases seeking to localize specific areas rely heavily on recent neuroanatomic observations, rather than Brodmann's reconstructions onto the convoluted human brain surface [23] . …”

A Proposed Number System for the 107 Cortical Areas of Economo and Koskinas, and Brodmann Area Correlations

“…9 Areas LA 1 -LA 3 , anterior cingulate gyrus. 10 Areas LB 2 , LF 1 and LF 2 belong to the supracommissural hippocampus [18]. 11 Areas LC 1 -LC 3 , posterior cingulate areas.…”