**3.2 Defined cytoarchitectonic fields**

12 Neuroimaging – Cognitive and Clinical Neuroscience

of Vienna (Triarhou, 2005, 2006), took cytoarchitectonics to a new zenith almost two decades after Brodmann's groundwork by defining 5 "supercategories" of fundamental structural types of cortex (agranular, frontal, parietal, polar, and granulous or *koniocortex*), subdivided into 54 *ground*, 76 *variant* and 107 cytoarchitectonic *modification* areas (von Economo & Koskinas, 1925, 2008), plus more than 60 additional intermediate *transition* areas (von

Topographically, the 107 Economo-Koskinas modification areas are subdivided into 35 frontal, 13 superior limbic, 6 insular, 18 parietal, 7 occipital, 14 temporal, and 14 inferior limbic or hippocampal. Moreover, the frontal lobe is subdivided into prerolandic, anterior (prefrontal), and orbital (orbitomedial) regions; the superior limbic lobe into anterior, posterior and retrosplenial regions; the parietal lobe into postcentral (anterior parietal), superior, inferior and basal regions; and the temporal lobe into supratemporal, proper, fusiform and temporopolar regions (von Economo, 2009; von Economo & Koskinas, 2008). The detailed cytoarchitectonic criteria of von Economo & Koskinas (1925, 2008) confer a clear advantage over Brodmann's scheme; their work represents a gigantic intellectual and technical effort (van Bogaert & Théodoridès, 1979), an attempt to bring the existing knowledge into a more orderly pattern (Zülch, 1975), and the only subdivision to be later acknowledged by von Bonin (1950) and by Bailey & von Bonin (1951). It is meaningful that basic and clinical neuroscientists adopt the Economo-Koskinas system of cytoarchitectonic areas over the commonly used Brodmann areas (see also discussion by Smith, 2010a, 2010b). Brodmann (1909; Garey, 2006) described the comparative anatomy and cytoarchitecture of the cerebral cortex in numerous mammalian orders, from the hedgehog—with its unusually large archipallium—up to non-human primate and human brains; he introduced terms such as *homogenetic* and *heterogenetic formations* to denote two different basic cortical patterns, which, respectively, are either derived from the basic six-layer type or do not demostrate the six-layer stage. Brodmann was intrigued by the phylogenetic increase in the number of cytoarchitectonic cortical areas in primates, and was astute in pointing out the phenomenon of phylogenetic regression as well (Striedter, 2005). Vogt & Vogt (1919) laid the foundations of fiber pathway architecture; they defined the structural features of allocortex, proisocortex, and isocortex, and extensively discussed the differences between paleo-, archi-, and

Combining cyto- and myeloarchitectonics, Sanides (1962, 1964) placed emphasis on the transition regions *(Gradationen)* that accompany the "streams" of neocortical regions coming from paleo- and archicortical sources (Pandya & Sanides, 1973). [Vogt & Vogt (1919) had already spoken of "areal gradations".] The idea of a "koniocortex core" and "prokoniocortex belt areas" in the temporal operculum (Pandya & Sanides, 1973) was modified by Kaas & Hackett (1998, 2000), who speak of histologically and functionally distinct "core", "belt" and

There are three major advantages in using the system of cytoarchitectonic areas defined by von Economo and Koskinas as opposed to the maps defined by Brodmann (von Economo,

Brodmann published his monograph in 1909. Von Economo began work on cytoarchitectonics in 1912, with Koskinas joining in 1919; their *Textband* and *Atlas* were published in 1925, almost two decades after Brodmann, and comprised 150 new discoveries

"parabelt" subdivisions in the monkey auditory cortex, with specified connections.

Economo, 2009; von Economo & Horn, 1930).

neocortical regions (Vogt & Vogt, 1919; Vogt, 1927; Zilles, 2006).

2009; Triarhou, 2007a, 2007b):

**3.1 Timing of publication** 

Brodmann defined 44 cortical areas in the human brain. Von Economo and Koskinas defined 107 areas (von Economo, 2009; von Economo & Koskinas, 2008), plus another more than 60 *transition* areas (von Economo, 2009), thus providing a greater "resolution" over the Brodmann areas for the human cerebral hemispheres by a factor of four. Brodmann correlations can be found in the *Atlas* (von Economo & Koskinas, 2008) and in a related review (Triarhou, 2007b).

### **3.3 Extrapolated versus real surface designations**

Brodmann maps are commonly used to either designate cytoarchitectonic areas as such, or as a "shorthand system" to designate some region on the cerebral *surface* (DeMyer, 1988). Macroscopic extrapolation of Brodmann projection maps are effected on the atlas of Talairach & Tournoux (1988), rather than being based on real microscopic cytoarchitectonics. Such a specification of Brodmann areas is inappropriate and may lead to erroneous results in delineating specific cortical regions, which may in turn lead to erroneous hypotheses concerning the involvement of particular brain systems in normal and pathological situations (Uylings et al., 2005). On the other hand, the unique sectioning method of von Economo and Koskinas, whereby each gyrus is dissected into blocks *always perpendicular to the gyral surface*, be it dome, wall or sulcus floor, essentially offers a "mechanical" solution to the generalized mapmaker's problem of flattening nonconvex polyhedral surfaces (Schwartz et al., 1989), one of the commonest problems at the epicentre of cortical research.

Furthermore, microscopically defined borders usually differ from gross anatomical landmarks, cytoarchitectonics reflecting the inner organisation of cortical areas and their morphofunctional correlates (Zilles, 2006). Despite the integration of multifactorial descriptors such as chemoarchitecture, angioarchitecture, neurotransmitter, receptor and gene expression patterns, as well as white matter tracts, it is clear that the knowledge of the classical anatomy remains fundamental (Toga & Thompson, 2007). The structure of cortical layers incorporates, and reflects, the form of their constitutive cells and their functional connections; the underpinnings of neuronal connectivity at the microscopic level are paramount to interpreting any clues afforded by neuroimaging pertinent to cognition.
