prefrontal cortex


Short definition

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Definition - HNS

Petrides  M. HNS2:


Prefrontal Cortex


On the medial surface of the frontal lobe, the cingulate and paracingulate regions are occupied by areas 24 and 32, respectively (Fig. 25.8B). Dorsal to these areas, on the medial surface of the superior frontal gyrus, in a caudorostral direction, lie the medial extensions of areas 8B, 9, and 10. Ventrally, area 32 borders the medial part of area 14, and caudally it abuts area 25, which occupies the subcallosal gyrus. In area 25, layer II has an irregular margin and is ill-defined (Fig. 25.13). Layer III contains small to medium-sized pyramidal cells that are sparsely distributed. Layers V and VI contain deeply stained neurons giving the infragranular layers a uniform appearance. Area 25, like area 24, is a proisocortical area by virtue of its prominent infragranular layers and the absence of layer IV.

In area 24, layer II has an irregular margin and is illdefined. Layer III contains small to medium pyramidal cells that are sparsely distributed. The striking feature of area 24 is layer V, which contains deeply stained medium to large pyramidal cells. This layer abuts layer III because of the absence of layer IV. Layer Vb and VI blend and contain medium to small pyramidal cells. Like area 25, area 24 is a proisocortical region because of the overall prominence of the infragranular layers and the absence of layer IV.


Area 32 surrounds area 24 and occupies a region that is often referred to as the paracingulate gyrus (Fig. 25.8). In area 32, as in areas 24 and 25, the infragranular layers predominate. Layer III of area 32 contains small to medium pyramidal cells and is denser than that of area 24. There is an incipient layer IV in area 32. Layer Va contains deeply stained neurons that are more dispersed than those of area 24. Layers V and VI are slightly separated. Area 32 exhibits minor variations that have been recognized by both Economo and Koskinas (1925) and Sarkissov et al. (1955). Each subdivision exhibits some of the features of the neocortical areas adjoining it. Area 32 can be considered as a transitional type of cortex between the isocortex and the proisocortical areas 24 and 25. For a more detailed discussion of the cingulate areas, see Chapter 24.


Architectonic Trends

The prefrontal architectonic areas described previously can be conceptualized as belonging to one of two general groups or trends. This conceptualization is based on the notion of the dual origin of the cerebral cortex, which has been proposed by

Dart (1934),

Abbie (1940),

Sanides (1969),

Pandya and Yeterian (1990), and

Barbas and Pandya (1989).


According to this concept, one cortical architectonic trend originates from the paleocortical (olfactory) moiety, whereas the other trend originates in the archicortical (hippocampal) moiety. From each one of these two allocortical moieties, a progressive laminar differentiation can be traced, passing through periallocortex and proisocortex toward the development of the true six-layered isocortex.


For the frontal cortical areas, the sites of origin are

(1) the allocortical, periallocortical and proisocortical areas in the caudal orbital frontal region and

(2) the allocortical, periallocortical, and proisocortical areas in the cingulate region around the rostral part of the corpus callosum.


From the proisocortex in the caudal orbital frontal region, which is characterized by a predominance of the infragranular layers and the absence of layer IV, the next stage of differentiation is area 13 which has an incipient layer IV. Next follow areas 14, 11, and orbital 47/12, which have a predominance of the infragranular layers V and VI and a better developed layer IV. Progressing further in terms of laminar differentiation are the adjacent cortical areas 10, lateral 47/12, and ventral portion of area 46, which are characterized by an approximately equal emphasis on the infra- and supragranular layers and further development of layer IV. Further differentiation within this trend can be seen in ventral area 9/46, ventral area 8 (i.e., 8Av), and area 45, all of which exhibit a predominance of the supragranular layers, prominent pyramidal neurons in layer III and highly developed layer IV.


The archicortical trend of prefrontal areas originates in the proisocortical areas 24, 25, and 32 in the anterior cingulate region. These areas exhibit a predominance of infragranular layers and virtually no layer IV. The next stage of differentiation is represented by the medial parts of isocortical areas 8B and 9, which have a poorly developed layer IV. The next stage of differentiation can be seen in lateral areas 8B, 9, and 10, which have a better developed layer IV and a relative equivalence of the infra- and supragranular layers. Finally, one observes areas 46, 9/46d, and 8Ad, which contain a highly developed layer IV and the predominance of supragranular layers. We would like to emphasize that within each stage of these two trends of architectonic differentiation, the various areas exhibit their own unique architectonic pattern. Although these two architectonic trends emerge from two distinct points of origin (i.e., the caudal orbitofrontal and the rostral cingulate regions), they come together in the region of the middle frontal gyrus.


Definition - other sources



Classical Architecture





Functional Anatomy

Clinical Anatomy



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