A Brodmann area is a region of the cerebral cortex defined based on its cytoarchitectonics, or structure and organization of cells.
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Brodmann areas were originally defined and numbered by the German anatomist Korbinian Brodmann based on the cytoarchitectural organization of neurons he observed in the cerebral cortex using the Nissl stain. Brodmann published his maps of cortical areas in humans, monkeys, and other species in 1909[1], along with many other findings and observations regarding the general cell types and laminar organization of the mammalian cortex. (The same Brodmann area number in different species does not necessarily indicate homologous areas[2].) A similar, but more detailed cortical map was published by Constantin von Economo and Georg N. Koskinas in 1925[3].
Brodmann areas have been discussed, debated, refined, and renamed exhaustively for nearly a century and remain the most widely known and frequently cited cytoarchitectural organization of the human cortex.
Many of the areas Brodmann defined based solely on their neuronal organization have since been correlated closely to diverse cortical functions. For example, Brodmann areas 1, 2 and 3 are the primary somatosensory cortex; area 4 is the primary motor cortex; area 17 is the primary visual cortex; and areas 41 and 42 correspond closely to primary auditory cortex. Higher order functions of the association cortical areas are also consistently localized to the same Brodmann areas by neurophysiological, functional imaging, and other methods (e.g., the consistent localization of Broca's speech and language area to the left Brodmann areas 44 and 45). However, functional imaging can only identify the approximate localization of brain activations in terms of Brodmann areas since their actual boundaries in any individual brain requires its histological examination.
(*) Area only found in non-human primates.
Some of the original Brodmann areas have been subdivided further, e.g., "23a" and "23b".[5]
When von Bonin and Bailey constructed a brain map for the macaque monkey they found the description of Brodmann inadequate and wrote:
They instead used the cytoarchitechtonic scheme of Constantin von Economo and Georg N. Koskinas published in 1925[7] which had the "only acceptable detailed description of the human cortex".
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