A Brodmann area is one of roughly 52 numbered regions on the surface of the human brain, each defined by its distinct microscopic cell structure. The German neurologist Korbinian Brodmann published his map in 1909 after years of painstaking work slicing and staining brain tissue, and more than a century later his numbering system remains the most widely used shorthand in neuroscience for referring to specific cortical zones. The map is far from perfect, and modern imaging has revealed the cortex is more finely divided than Brodmann could see with his microscope, yet the original labels persist in research papers, surgical planning, and textbooks because they give scientists and clinicians a common language for talking about where something is happening in the brain.
How the Original Map Was Made
Brodmann began his mapping work in Berlin around 1901 under the direction of the neuroanatomists Oskar and Cécile Vogt. The project was technically demanding: the team had to design their own large microtome, improve tissue-embedding and staining methods, and develop new photographic techniques to prepare complete series of brain sections, each roughly 20 to 30 micrometers thick, sometimes producing several thousand sections from a single hemisphere.1PubMed Central. Brodmann: a pioneer of human brain mapping—his impact on concepts of cortical organization Brodmann stained those sections for cell bodies using a Nissl-type method and then examined, under the microscope, how the arrangement and density of neurons changed from one patch of cortex to the next. Wherever he saw a consistent shift in the pattern of cell layers, he drew a boundary and assigned a number.
The result was a flat map with 52 distinct areas (some numbers were later reserved for non-human species, which is why you will sometimes see gaps in the human numbering). Each area was defined entirely by its cytoarchitecture, the physical arrangement of cells, without any functional data from living subjects. That Brodmann’s structural boundaries later turned out to align, in many cases, with regions that do genuinely different things was a remarkable validation of the idea that form follows function in the cortex.
Movement and Touch
Brodmann area 4 sits along the precentral gyrus, the ridge just in front of the central sulcus, and corresponds to the primary motor cortex. For a long time it was treated as a single uniform strip, but research using both microscopy and brain imaging has shown it can be split into two sub-zones: an anterior part (4a) and a posterior part (4p). These sub-areas differ in their cell architecture, the density of neurotransmitter receptors, and their function. Positron emission tomography revealed that both contain separate representations of the fingers, and that the posterior sub-area responds more strongly during tasks like roughness discrimination.2PubMed. Two different areas within the primary motor cortex of man Functional MRI work further showed that the posterior part is modulated by whether you are paying attention to what your hand is doing, while the anterior part fires similarly regardless of attention.3PubMed. Neural activity in human primary motor cortex areas 4a and 4p is modulated differentially by attention to action
Just behind the central sulcus, Brodmann areas 1, 2, and 3 make up the primary somatosensory cortex, the region that processes what you feel when you touch something. These three strips are not interchangeable. Area 3 responds most directly to raw tactile input, area 1 is more involved in the texture and edge features of what you touch, and area 2 integrates pressure, joint position, and shape. Imaging experiments have even demonstrated that areas 1 and 2 contribute differently to a person’s sense of body ownership, with distinct finger-topographic selectivity between the hand doing the touching and the hand being touched.4PubMed Central. Distinct contributions of Brodmann areas 1 and 2 to body ownership
Seeing and Hearing
Brodmann area 17, also called the striate cortex or V1, occupies the banks of the calcarine fissure at the very back of the brain. It is the first cortical stop for visual information coming from the eyes, and it contains an orderly map of the visual field: every neighboring point you see corresponds to a neighboring cluster of neurons in area 17. This point-by-point retinotopic mapping has been confirmed electrophysiologically and matches the cytoarchitectonic boundaries almost perfectly.5PubMed. The retinotopic organization of area 17 (striate cortex) in the cat Surrounding areas 18 and 19 handle progressively more complex visual processing, such as recognizing motion, color, and shape.
For hearing, areas 41 and 42 sit on the superior temporal gyrus, largely tucked inside a fold called Heschl’s gyrus, and serve as the primary auditory cortex. Their fundamental job is frequency analysis: sorting incoming sound by pitch, much as the visual cortex sorts by location in space. Precisely how the frequency map (tonotopy) is laid out in humans remained debated for years, partly because the anatomy of Heschl’s gyrus varies so much between people, but recent work comparing human imaging data with detailed tracing studies from other primates has brought the picture into sharper focus.6PubMed. The Map of Auditory Function
Language Production and Comprehension
Perhaps the most famous pair of Brodmann areas is 44 and 45, which together form Broca’s area in the left inferior frontal gyrus. Damage here classically produces halting, effortful speech with relatively preserved comprehension. Functional imaging combined with probabilistic cytoarchitectonic maps has revealed that the two areas divide labour: area 45 is more involved in the semantic side of language, such as selecting the right word for the right meaning, while area 44 handles higher-level programming of the motor sequences needed to actually produce speech.7PubMed. Analysis of neural mechanisms underlying verbal fluency in cytoarchitectonically defined stereotaxic space–the roles of Brodmann areas 44 and 45 This division holds even for signed language: in bilingual individuals fluent in both spoken English and American Sign Language, area 45 was activated during narrative production in both modalities, while area 44 was activated by the complex movements of articulation, whether oral or manual.8PubMed. Activation of Broca’s area during the production of spoken and signed language: a combined cytoarchitectonic mapping and PET analysis
On the comprehension side, Wernicke’s area sits in the posterior part of the superior temporal gyrus, overlapping area 22 in the left hemisphere. It is essential for processing both auditory and visual language input and integrating meaning with sentence structure.9PubMed Central. From Sound to Meaning: Navigating Wernicke’s Area in Language Processing But the reality is messier than the textbook picture of a neat production region up front and a neat comprehension region in the back. A meta-analytic review of functional imaging studies proposed that a “core” Wernicke’s area for word recognition involves areas 21, 22, 41, and 42, while an extended network encompassing areas 20, 37, 38, 39, and 40 handles associating words with broader meanings and context.10Archives of Clinical Neuropsychology. How Localized are Language Brain Areas? A Review of Brodmann Areas Involvement in Oral Language Language, in short, is not confined to two tidy zones; it sprawls across a wide web of cortex.
Planning, Monitoring, and the Prefrontal Cortex
The prefrontal cortex, which takes up a large swath of the frontal lobe, contains many Brodmann areas (including 9, 10, 11, 12, 46, and 47), and it is broadly responsible for the kinds of things people mean when they say “executive function”: planning, decision-making, holding information in mind, and switching between tasks. Neuroimaging and lesion studies have teased apart at least two functional clusters within it. The mid-dorsolateral prefrontal cortex is involved in monitoring what is being held in working memory, while the mid-ventrolateral prefrontal region helps with making active judgments about that information and with encoding and retrieving it.11PubMed Central. Lateral prefrontal cortex: architectonic and functional organization
Nearby, the anterior cingulate cortex, which includes areas 24 and 32, plays a complementary role. Rather than holding plans or selecting actions, it monitors how those actions are going. Imaging experiments using tasks that create conflicting response demands have shown that the anterior cingulate becomes especially active when you respond to an incongruent stimulus, consistent with a role in flagging errors or conflicts so the prefrontal cortex can adjust.12PubMed. Dissociating the role of the dorsolateral prefrontal and anterior cingulate cortex in cognitive control
The Posterior Parietal Cortex as an Integration Hub
Areas 5, 7, 39, and 40 make up the posterior parietal cortex, a region that is neither purely sensory nor purely motor. Instead, it acts as an association zone, pulling together signals from somatosensory, auditory, visual, motor, cingulate, and prefrontal cortices, along with proprioceptive and vestibular information from deeper in the brain.13Current Biology. Posterior parietal cortex This is the region that helps you reach accurately for a coffee cup without thinking about the geometry involved, or that lets you understand where your body is in space. Damage here can produce striking deficits, including an inability to attend to one side of space or difficulty coordinating eye and hand movements despite intact vision and motor strength.
Why the Borders Don’t Line Up Perfectly Across People
One of the oldest criticisms of Brodmann’s map is that it implies fixed, universal boundaries. In reality, the cortical areas vary substantially from person to person. Studies that have mapped primary visual areas 17 and 18 in three-dimensional stereotaxic space found high individual variability in the size, shape, and relationship of these areas to visible sulci and gyri on the brain surface.14PubMed. Brodmann’s areas 17 and 18 brought into stereotaxic space-where and how variable? Some of this variability is predictable from the visible landmarks on the cortex, but some is not, meaning you cannot always tell where an area begins just by looking at the folds.15Cerebral Cortex. Topographical Variation of the Human Primary Cortices: Implications for Neuroimaging, Brain Mapping, and Neurobiology
The variability is not limited to sensory cortex. Heteromodal association areas in the prefrontal cortex show similarly large differences in their three-dimensional location across individuals, even after correcting for brain size and shape.16PubMed. Consequences of large interindividual variability for human brain atlases: converging macroscopical imaging and microscopical neuroanatomy This is why modern neuroimaging studies use probabilistic maps rather than hard-edged outlines: instead of saying “area 44 lives exactly here,” the map says “there is a 60 percent probability that this voxel belongs to area 44 in a given person.”
The Modern Update to 180 Areas Per Hemisphere
If Brodmann could see about 52 distinct areas with his microscope and staining methods, modern multi-modal imaging can see far more. A landmark study from the Human Connectome Project used MRI data from 210 healthy young adults to delineate 180 areas per hemisphere, identifying boundaries based on sharp changes in cortical architecture, function, connectivity, and surface topography. Of those 180 areas, 83 matched regions previously described by post-mortem microscopy or other specialized approaches, while 97 were newly characterized.17PubMed Central. A multi-modal parcellation of human cerebral cortex The boundaries proved robust: the vast majority had large effect sizes across multiple feature categories, meaning they were not statistical flukes.
This newer parcellation does not replace Brodmann’s numbering so much as refine it. In many cases a single Brodmann area, like area 6 (the premotor cortex), gets broken into several smaller parcels that differ in connectivity or function. Researchers increasingly use these finer-grained maps, but when they need to communicate quickly about a general cortical neighborhood, they still reach for Brodmann’s numbers.
Chemical Fingerprints Add Another Layer
Brodmann’s original distinctions were based on how cells are arranged. A newer approach called receptor architectonics asks a different question: how densely are various neurotransmitter receptors expressed across the cortical layers? When researchers measured the densities of multiple receptor types across cortical areas, they found that each area has a characteristic “receptor fingerprint,” a unique profile of how much glutamate, GABA, serotonin, dopamine, and other receptor types are present in its different layers.18Frontiers in Neuroanatomy. Multiple Transmitter Receptors in Regions and Layers of the Human Cerebral Cortex These chemical profiles often confirm Brodmann’s borders and sometimes reveal additional boundaries he missed, providing independent evidence that the parcellation is real and not just a quirk of how you measure cells.
Why the Map Matters for Neurosurgery
For neurosurgeons removing a brain tumor, knowing exactly where the primary motor cortex starts and the premotor cortex ends can be the difference between a patient walking out of the hospital and a patient with permanent weakness. Cortical-thickness measurements based on Brodmann areas 4 and 6 can help surgeons localize the motor cortex on preoperative scans, which is especially valuable when swelling from the tumor distorts the normal landmarks that would otherwise guide them to the central sulcus.19PubMed Central. Anatomical Parcellations of Brodmann’s Areas 4 and 6: A Study on Cortical Thickness for Improved Neurosurgical Planning
During awake craniotomies for glioma removal, surgeons now compare preoperative functional MRI activation maps with direct electrical stimulation of the exposed cortex, often classifying the results using the finer Human Connectome Project parcellation to see which specific sub-area corresponds to a given function.20Journal of Neurosurgery. Cortical mapping in glioma surgery: correlation of fMRI and direct electrical stimulation with Human Connectome Project parcellations The interplay between old and new maps is practical: Brodmann’s numbers orient the conversation, and the newer parcellations sharpen the knife.
How Brodmann Areas Develop After Birth
Not all Brodmann areas are fully mature at birth. Broca’s area is an instructive example. Cytoarchitectonic analysis of developing brains has shown that the distinction between areas 44 and 45 requires at least two, and probably three, years of postnatal life to reach its adult form.21PubMed. Adult structure and development of the human fronto-opercular cerebral cortex (Broca’s region) This timeline is interesting because it roughly parallels the period when children transition from babbling and single words to combining words into sentences. It does not prove that maturation of these areas causes language milestones, since many brain regions develop in parallel, but the overlap is suggestive.
Evolutionary Clues From Comparing Species
Brodmann areas are not unique to humans; homologous regions can be identified in other primates, though the proportions change dramatically. A comparative analysis across primate species found that Old World monkeys, apes, and humans share a distinctive evolutionary trend: disproportionate expansion of the frontal and parietal lobes relative to the occipital and temporal lobes. The prefrontal cortex was the principal driver of frontal expansion, and while humans carry the largest frontal and parietal lobes, this expansion follows a trajectory shared with other catarrhine primates rather than being a uniquely human leap.22PubMed Central. Multilevel atlas comparisons reveal divergent evolution of the primate brain
Within Broca’s area specifically, the basic cytoarchitectonic layout of areas 44 and 45 is recognizable in humans, chimpanzees, gorillas, orangutans, and macaques. The critical difference is not in the types of cells present but in the space between them. Humans have the largest neuropil volume relative to cell bodies, meaning there is considerably more room for the dendrites, axons, and synapses that enable local and long-distance connectivity.23PubMed. Differences in cytoarchitecture of Broca’s region between human, ape and macaque brains Great apes have markedly less, and macaques less still.24PubMed. A comparative quantitative analysis of cytoarchitecture and minicolumnar organization in Broca’s area in humans and great apes In other words, the blueprint of Broca’s area is ancient, but the wiring density that supports human language fluency is a relatively recent evolutionary addition. The neuropil expansion is one of the clearest structural differences between the human cortex and that of our closest relatives, and it tracks with the vastly richer connectivity that underlies our capacity for complex language and abstract thought.