Brodmann areas are a division of the human cerebral cortex based on cellular architecture. Areas with the same cellular structure form a Brodmann area. The brain is divided into 52 Brodmann areas.
What is a Brodmann area?
The brain of all living things appears as a monotonous and fatty mass, therefore white in color. Although it has been suspected since ancient times that this organ is the seat of perceptions and thought, until the 19th century it was impossible to gain any insight into how these abilities might be realized in the brain. It was only through special staining techniques developed by Antonio Golgi, Ramon y Cajal and Franz Nissl that the structure of brain cells called neurons could be made visible. Golgi’s staining revealed the great variety of forms of neurons and their many branches called dendrites and axons. In addition to the diversity of individual cell types, there are large local differences in the arrangement of these cells, which occur in clusters or layers of varying thickness and density. These quantitative differences can be well visualized using Nissl staining, the methodological basis of Korbinian Brodmann’s work. Brodmann examined the arrangement, density, and size of neurons in the human cortex and divided it into 52 areas based on local differences.
Anatomy and structure
If you look at the human brain from the outside, the main thing you see is the cortex (Latin for bark) overgrowing the rest of the brain, with its characteristic walnut shape. The cortex emerged last in the evolution of the brain and is most developed in humans. The brain has a pattern of sulci (lat. ditches) and gyri (gr. coils) as well as the sulcus centralis (lat. middle ditch) which separates the two cerebral hemispheres. On the basis of these features, each cerebral hemisphere can be divided into 4 lobes, the anterior (frontal), the superior (parietal), the posterior (occipital) and the lateral (temporal) lobes. This division is important for localizing neuronal brain structures, but not for understanding their function. To better link the anatomy of the cerebral cortex to its function, Korbinian Brodmann stained all cell bodies with the Nissl stain and examined brain sections with a microscope. The cortex exhibits a layering of cells with 3 to 5 layers, whose thickness and cell density can vary, as can the size of the cell bodies. Based on this microanatomy, Brodmann was able to identify 52 areas, which he designated with consecutive numbers. Brodmann published his results in 1909 in the paper “Comparative Localization Theory of the Cerebral Cortex.” Brodmann succeeded in this classification without developing a deeper understanding of the cell types and their interconnection in the individual areas. Developing this understanding is the main task of modern neuroscience.
Function and tasks
By comparing the cell structure of different brain areas, function cannot be inferred, and at Brodmann’s time little was known about the precise task of different brain regions in humans. In the years following Brodmann’s work, extensive knowledge about the function of different brain regionszu began to be gathered. The effects of brain damage, which occurred in large numbers during the two world wars, were the first extensive sources of neuromedical research. After the Second World War, targeted electrical stimulation of different brain areas during and after operations served to elucidate the function of various brain regions; these were supplemented with animal experiments. Nowadays, precise functions can be attributed to most Brodmann areas. In general, certain types of functions can be assigned to the four cerebral lobes already discussed. The frontal cortex is associated with our personality and thinking; damage to this brain area leads to personality changes and mental retardation. The parietal parietal lobe includes our body motor and sensory functions, while the occipital lobe at the back of the head contains what is known as the visual cortex. At the sides, in the temporal lobe of the brain, the abilities to hear and speak as well as parts of the memory are located.Here, the motor cortex that controls our limbs corresponds to Brodmann area 7, our ability to see to area 17, and areas 44 and 45 correspond to Broca’s area, damage to which is associated with a loss of linguistic expression.
Diseases
The classification of Brodmann areas is not primarily for diagnostic purposes or for any therapeutic intervention. However, by identifying corresponding functions of Brodmann areas, they have become an important diagnostic tool that can provide information about the location and extent of brain damage. For example, by corresponding function to brain area, the location of brain stroke can be determined in stroke patients based on the impairment. In modern imaging techniques that record brain activity, such as functional magnetic resonance imaging, knowledge of Brodmann areas is important because it allows signals to be assigned to brain functions. When planning surgical interventions on the brain, Brodmann areas and their functions are used as a basis for weighing how an intervention can be performed without affecting particularly important brain functions. The combination of state-of-the-art magnetic brain stimulation techniques (transcranial magnetic stimulation) with imaging techniques makes it possible to assess which areas of a Brodmann area have already been destroyed and can therefore be surgically removed and which cannot. The division of the brain into Brodmann areas is therefore widely used in modern neurobiological diagnostics and research.
