In search of the definitive Brodmann's map of cortical areas in human

The birth of the cytoarchitectonics (in Korbinian Brod- mann's own words cytoarchitectonics should be defined as "the localization of the individual histological ele- ments, their layering, and their parcellation in the adult brain") of the human cerebral cortex is credited to Mey- nert, who in 186721868, by using one of the first syn- thetic colors, Prussian (Berlin) blue (in painting, Parisian blue, Fe4(Fe(CN)6)3, derived from hydrogen cyanide or "blue acid"), noticed regional variations in the nerve cells stratification in different parts of the gray matter of the cerebral hemispheres (Meynert, 1868). During the 20th century, many investigators, including Camp- bell (1903), Brodmann (1909, 1910; for review see Judaet al., 2012), Elliot Smith (1907), von Economo and Koskinas (1925), Vogt and Vogt (1926), Bailey and von Bonin (1951), Sarkisov et al. (1955), and others, have produced cytoarchitectural maps of the human cerebral cortex by dividing it into a number of areas or fields. For this purpose, they were generally used the Nissl staining method, which is based on "defatting" brain tissue sections by passing through graded dilu- tions of ethanol, rehydrating through decreasing ethanol concentrations, and staining in a water solution of a cationic dye (such as methylene blue, cresyl violet, thio- nin, toluidine blue). The ethanol solutions act to differ- entiate the stain, causing myelin and other components to lose color and be "stripped off the cells", whereas negatively charged molecules within cell bodies retain the coloration (Nissl, 1894). Although many maps have been produced in attempts to make a definitive parti- tion of the human cerebral cortex, Brodmann's map and especially his numerical system attached to cytoarchitecture is by far the most widely recognized in current use. The last (final) Brodmann's map of the human cerebral cortex is shown in Figure 1A2C, and the list of cortical areas defined by Brodmann is pro- vided in Table 1. There is a common agreement that the popularity of Brodmann's numbering system is due to its simplicity to recall, its relatively sharp delineations of the borders between adjacent areas, its detail not so exhaustive to be impossible to refer to, and the fact that Brodmann's observations of cytoarchitecture have stood the test of time. In addition, Brodmann's map is also the closest to the modern definition of the cortical area (field), by which an area, among several other features, is receiv- ing afferent fibers from a particular (principal) nucleus of the thalamus (Jones, 1985, 2009). Thalamic inputs, except for the so-called nonspecific thalamic nuclei, stop abruptly at an areal border, and there appears to be no overlap between inputs from different specific thalamic nuclei to adjacent fields (Jones, 1985, 2009). Moreover, the chemoarchitectural borders, as defined by a characteristic pattern of histochemical or immuno- cytochemical staining, also commonly coincide with the cytoarchitecture defined by Brodmann. It is therefore not surprising that modified versions of Brodmann's map, often based on its extrapolation onto the Talairach and Tournoux brain atlas (Talairach and Tournoux, 1988), are so frequently used in neuroimaging studies to describe the localization of activation (Zilles and Amunts, 2010). In practice, however, this led to the occurrence of consistent mistakes and misinterpreta- tions in relation to usage and quotation of Brodmann's maps and numbers. Brodmann published a series of comparative neuroana- tomical works on more than 60 mammalian species in the Journal f € Psychologie und Neurologie between 1903 and 1908. These findings were summarized in his famous book (Brodmann, 1909) and extended in two chapters, which he contributed to contemporary handbooks (Brodmann, 1910, 1914). The first ("original") Brodmann's cytoarchitectonic map was first published in one of his monographs (Brodmann, 1908a) and then reproduced in his 1909 book, when he also added the map of the