Brodmann area | |
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![]() 3D representation of Brodmann areas | |
Details | |
Part of | Cerebrum |
Identifiers | |
NeuroNames | 427 |
FMA | 68596 |
Anatomical terms of neuroanatomy |
ABrodmann area is a region of thecerebral cortex, in thehuman or otherprimatebrain, defined by itscytoarchitecture, orhistological structure and organization ofcells. The concept was first introduced by the German anatomistKorbinian Brodmann in the early 20th century. Brodmann mapped the human brain based on the varied cellular structure across the cortex and identified 52 distinct regions, which he numbered 1 to 52. These regions, or Brodmann areas, correspond with diverse functions including sensation, motor control, and cognition.[1]
Brodmann areas were originally defined and numbered by theGermananatomistKorbinian Brodmann based on thecytoarchitectural organization ofneurons he observed in the cerebral cortex using theNissl method of cell staining. Brodmann published his maps of cortical areas in humans, monkeys, and other species in 1909,[2] along with many other findings and observations regarding the general cell types andlaminar organization of the mammaliancortex. The same Brodmann area number in different species does not necessarily indicatehomologous areas.[3] A similar, but more detailed cortical map was published byConstantin von Economo andGeorg N. Koskinas in 1925.[4]
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 theprimary somatosensory cortex; area 4 is theprimary motor cortex; area 17 is theprimary visual cortex; and areas 41 and 42 correspond closely toprimary auditory cortex.Higher order functions of theassociation cortical areas are also consistently localized to the same Brodmann areas byneurophysiological,functional imaging, and other methods (e.g., the consistent localization ofBroca's speech and language area to the leftBrodmann 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 require itshistological examination.
Different parts of the cerebral cortex are involved in different cognitive and behavioral functions. The differences show up in a number of ways: the effects of localized brain damage, regional activity patterns exposed when the brain is examined using functional imaging techniques, connectivity with subcortical areas, and regional differences in the cellular architecture of the cortex.Neuroscientists describe most of the cortex—the part they call theneocortex—as having six layers, but not all layers are apparent in all areas, and even when a layer is present, its thickness and cellular organization may vary. Scientists haveconstructed maps of cortical areas on the basis of variations in the appearance of the layers as seen with a microscope. One of the most widely used schemes came fromKorbinian Brodmann, who split the cortex into 52 different areas and assigned each a number (many of these Brodmann areas have since been subdivided). For example, Brodmann area 1 is the primary somatosensory cortex, Brodmann area 17 is the primary visual cortex, and Brodmann area 25 is the anterior cingulate cortex.[5]
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Many of the brain areas defined by Brodmann have their own complex internal structures. In a number of cases, brain areas are organized intotopographic maps, where adjoining bits of the cortex correspond to adjoining parts of the body, or of some more abstract entity. A simple example of this type of correspondence is the primary motor cortex, a strip of tissue running along the anterior edge of thecentral sulcus. Motor areas innervating each part of the body arise from a distinct zone, with neighboring body parts represented by neighboring zones[6]. Electrical stimulation of the cortex at any point causes a muscle-contraction in the represented body part. This "somatotopic" representation is not evenly distributed, however; the head, for example, is represented by a region about three times as large as the zone for the entire back and trunk. The size of any zone correlates to the precision of motor control and sensory discrimination possible. The areas for the lips, fingers, and tongue are particularly large, considering the proportional size of their represented body parts.
The maps for visual areas areretinotopic[7][8], meaning that they reflect the topography of theretina: the layer oflight-activated neurons lining the back of the eye. In this case too, the representation is uneven: thefovea—the area at the center of the visual field—is greatly overrepresented compared to the periphery. The visual circuitry in the human cerebral cortex contains several dozen distinct retinotopic maps, each devoted to analyzing the visual input stream in a particular way. The primary visual cortex (Brodmann area 17), which is the main recipient of direct input from the visual part of the thalamus, contains many neurons that are most easily activated by edges with a particular orientation moving across a particular point in the visual field. Visual areas farther downstream extract features such as color, motion, and shape.
In auditory areas, the primary map istonotopic[9]. Sounds are parsed according to frequency (i.e., high pitch vs. low pitch) by subcortical auditory areas, and this parsing is reflected by the primary auditory zone of the cortex. As with the visual system, there are a number of tonotopic cortical maps, each devoted to analyzing sound in a particular way.
Within a topographic map there can sometimes be finer levels of spatial structure. In the primary visual cortex, for example, where the main organization is retinotopic and the main responses are to moving edges, cells that respond to different edge-orientations are spatially segregated from one another.
(*) Area only found in non-humanprimates.
Some of the original Brodmann areas have been subdivided further, e.g., "23a" and "23b".[11]
When von Bonin and Bailey constructed a brain map for themacaque monkey, they found the description of Brodmann inadequate and wrote: "Brodmann (1907), it is true, prepared a map of the human brain which has been widely reproduced, but, unfortunately, the data on which it was based was never published"[12] They instead used the cytoarchitectonic scheme ofConstantin von Economo andGeorg N. Koskinas published in 1925[4] which had the "only acceptable detailed description of the human cortex".