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Cingulate Gyrus Overview

Cingulate Gyrus: Cingulate Maps


Cortical histologists study the details of each part of the cortex and need a means of reconstructing these findings in a way that investigators in other areas of neuroscience can easily access.  Most maps of the cortical areas are reconstructions onto the convoluted brain surface because relationships between surface morphologies and areas are most easily appreciated. The strength of this strategy is that the location of areas are easily related to gross morphology, however, the drawback is that about 50% of the cortex is in the depths of sulci that are not represented on surface reconstructions. A partial solution to this problem is provided by flat mapping techniques. Although numerous maps of the distribution of areas on the human cingulate gyrus have been published over the past century, none have employed a flat map technique. In addition to the Brodmann map, three are selected here because they each played an important role in defining the cingulate cortical areas. These particularly cogent maps include those of von Economo and Koskinas (1925), Sarkisov et al. (1955), and Braak (1980) and are presented in Figure 1.  Let us consider each one briefly as it relates to structural heterogeneity in the cingulate gyrus and try to interpret some of the issues relating to sulcal areas.

von Economo and Koskinas (1925) identified areas LA2 and LA that share similarities with the distributions of perigenual ACC and MCC. Their areas LC1 and LC2 appear to be similar to Brodmann areas 31 and 23, while areas LD and LE are retrosplenial areas on the ventral bank of the cingulate gyrus.  It is also interesting that they viewed changes on the medial surface as reflecting fundamental differences along the frontal lobe. Although Brodmann stated that area 32 is a dorsal and anterior cingulate area (1909), this area has transitional features of what might also be termed cingulofrontal transition cortex. Finally, LC2 extends further rostrally than does area 23 of PCC. Sarkisov et al. (1955) observed a transition between areas 24 and 23 and difficulty identifying the exact point at which layer IV appears may contribute to some difficulty identifying the exact rostrocaudal point of this border. Finally, von Economo and Koskinas (1925) identified anterior ectogenual area LA3 and ectosplenial area LF which likely equate to Brodmann’s areas 33 and 26, respectively.

Figure 1.  Some maps of the cingulate gyrus have played an important role in recent thinking about the cytoarchitectural organization of the cingulate gyurs.  These include the maps of von Economo and Koskinas (1925),  Sarkisov et al. (1955), and Braak (1980).

The map of Sarkisov et al. (1955) was particularly important to early work in the monkey because these investigators identified parallel, ventral-to-dorsal subdivisions of areas 24 and 23 in human that we first observed in monkey (Vogt et al., 1987) and later in human (Vogt et al., 1995). The major difference is that we observe only two gyral parts of each area (i.e., areas 24a and b and 23a and b) and the third subdivision of each is areas 24c and 23c is in the cingulate sulcus.  It is possible that use of the convoluted surface by Sarkisov et al. (1955) meant they had to represent the sulcal area on the gyral surface to maintain the gross morphological integrity of the medial surface.  This would not be true for area 23c, however, which stretches along the ventral border of area 31.  We continue to view area 23c as a caudal extension of cingulate sulcal cortex and we agree with Brodmann that area 31 surrounds the splenial sulci.  Finally, Sarkisov et al. extend all three divisions of area 24 into the subgenual region. Photographs are provided later suggesting that this cortex is a variation of area 25 and it is not likely that areas 24a, b and c are all represented in the SGSR.

Three important contributions of Heiko Braak (1980) to the understanding of cingulate cytoarchitecture are included in his map (Fig. 1C). First, this map shows the prominent anterogenual magnoganglionic area in perigenual ACC and suggests that the perigenual part of Brodmann’s area 24 is quite distinct from its caudal extent. Indeed, it is possible that the differences belie a fundamental pattern of cortical differentiation as proposed by Braak. Second, the primitive gigantopyramidal field is located in the cingulate sulcus and is now recognized as forming a cingulate motor area with corticospinal projections. Third, the retrosplenial areas are located on the ventral bank of the cingulate gyrus in the depths of the callosal sulcus, while parasplenial isocortex (ps) surrounds the RSC. It appears that ps closely approximates but is not equivalent to area 23a.

Each of the three maps in Figure 1 has made important contributions to our understanding of the cingulate gyrus. Although Brodmann’s map (1909) played a significant role in human brain research, it needs substantial revision before it can be applied to modern studies of human brain function.  The present overview seeks to highlight the strong points in Brodmann’s perspective and then modify it according the maps in Figure 1, connection patterns observed in the monkey brain, and the past decade of functional imaging research.

Brodmann’s Map

The Brodmann map has become the most frequently used point of reference in human neuropathology and imaging studies partially because Talairach and Tournoux (1988) extrapolated it onto a standardized brain atlas. Unfortunately, there are difficulties interpreting the Brodmann map, it was limited to a single case, the reconstruction was onto the convoluted cortex without delineation of areas in the sulcal depths which accounts for about 50% of the cortical surface area, and the Talairach and Tournoux (1988) atlas made transpositions that are not consistent with the histological facts. As can be seen in the maps in Figure 1, the Brodmann nomenclature is only one view of medial cortex and there have been numerous morphological and functional studies over the past 100 years suggesting this map needs modification.

Figure 2. The Brodmann map (1909) is one of the most influential maps of the medial surface. To assess the structure of each area in celloidin-embedded and Nissl-stained sections, centroids were identified for the major areas and photographed for levels A-F.  The corpus callosum (CC) and layer V (asterisks) are noted. The centroid photographs provide benchmarks to which each cytoarchitectural area is compared in immunohistochemical preparations.

Figure 2 shows Brodmann’s map of the dorsomedial cortex. There are 6 circles on this map that reference places where low magnification photographs were taken in a case that had been embedded in celloidin and stained with cresylecht violet. Since Brodmann did not provide microphotographic documentation of all areas in his map of human medial cortex, the topographic center of each area needs to be identified and photographed to serve as the standard for detailing its histological properties. It is from this centroid analysis that modifications are made to define cytoarchitecturally uniform subareas. In some instances, there is doubt as to which structure constituted a Brodmann area. For example, his area 33 could refer to an area in the depths of the callosal sulcus which is an ectogenual area, it could refer to an area on the edge of the ventral bank of the cingulate gyrus which we refer to as area 24a, or it could be a combination of both.  In this instance, we concur with Zilles (1990) who suggests it is an ectogenual area.

The Brodmann area centroids were located from his map by finding the approximate rostrocaudal and dorsoventral midpoint for each area on his map and in equivalent locations in a celloidin-embedded/Nissl-stained case (Fig. 2). Area 33 wraps completely around the genu of the corpus callosum and is likely an ectogenual area with a single layer of pyramidal neurons that abuts the indusium griseum dorsally and area 24 ventrally (Fig. 2A, B, D). Area 25 is agranular (lacks a layer IV) and has two principal layers of neurons; a superficial layer II/III that is relatively uniform in its density of medium-sized pyramidal neurons and a deep pyramidal layer of medium-large pyramids similar to those mainly in layer V; only a small layer VI is present (Fig. 2A). One of the most consistent features of cingulate architecture is the prominence of layer V, particularly in ACC. The relative prominence of layer Va is most evident in area 24 as shown in Figure 7B/D with asterisks. Finally, area 32 is a dorsal and anterior cingulate subdivision that surrounds the rostral and dorsal edges of area 24.  It is a dysgranular area with a thin and variable layer IV (Fig. 2B, C).

The posterior cingulate gyrus is comprised of two regions, retrosplenial areas 29 and 30 on the ventral bank of the cingulate gyrus and posterior cingulate areas 23 and 31 on the cingulate gyral surface and depths of the caudal cingulate sulcus. The ectosplenial area 26 is located at the fundus of the callosal sulcus. Ectosplenial cortex is essentially a single, external layer of neurons that have a granular appearance and are similar to neurons in the external granular layer of retrosplenial area 29. Area 29 has a granular external pyramidal layer and an undifferentiated layers V and VI (Fig. 2F).  Brodmann referred to area 30 as “agranular;” a concept that is challenged in detail below.  Finally, area 23 on the posterior cingulate gyral surface is clearly granular, while area 31 surrounds the splenial sulci and has the thickest and most granular layer IV in posterior cingulate cortex (Fig. 2F, E, respectively) If immunohistochemical, connection, and functional studies observed homogeneity within each of these Brodmann areas, nothing more would need to be said about the architecture of the cingulate gyrus.  However, almost none of the Brodmann areas are cytologically uniform and it appears that a full century of neuroscience requires that we modify this map in substantive ways; a process that is ongoing and will probably take another few decades.

References

Braak, H. (1980). "Architectonics of the Human Telencephalic Cortex." Springer-Verlag, Berlin.

Brodmann, K. (1909). "Vergleichende Lokalisationslehre der Grosshirnrinde in ihren Prinzipien dargestellt auf Grund des Zellenbaues." Barth, Leipzig.

von Economo, C. and Koskinas, G. N. (1925). "Die Cytoarchitektonik der Hirnrinde des erwachsenen Menschen." Springer, Berlin.

von Economo, C. (1929). "The Cytoarchitectonics of the Human Cerebral Cortex." Oxford University Press, London.

Sarkisov, S. A., Filimonoff, I. N., Kononowa, E. P., Preobraschenskaja, I. S., and Kukuew, E. A. (1955). "Atlas of the cytoarchitectonics of the human cerebral cortex." Medgiz, Moscow.

Talairach, J. and Tournoux, P. (1988). "Co-Planar Stereotaxic Atlas of the Human Brain." Thieme Medical Publishers, New York.

Vogt, B. A., Nimchinsky, E. A., Vogt, L. J., and Hof, P. R. (1995). Human cingulate cortex:  Surface features, flat maps, and cytoarchitecture. J.Comp.Neurol. 359, 490-506.

Vogt, B. A., Pandya, D. N., and Rosene, D. L. (1987). Cingulate cortex of the rhesus monkey:  I. Cytoarchitecture and thalamic afferents. J.Comp.Neurol. 262, 256-270.

Vogt, B. A., Pandya, D. N., and Rosene, D. L. (1987). Cingulate cortex of the rhesus monkey:  I. Cytoarchitecture and thalamic afferents. J.Comp.Neurol. 262, 256-270.

Zilles, K. (1990). Cortex. In "The Human Nervous System" (G. Paxinos, Ed.), pp. 757-802. Academic Press, Inc., Sydney.


copyright 2004-2009 Cingulum NeuroSciences Institute. All rights reserved.
Brent A. and Leslie J. Vogt. bvogt@twcny.rr.com