Seven-tenths of the volume of the human nervous system lies in the cerebral cortex. Given that the human cortex is many times larger than that of any other creature, scientists are convinced its huge size is the main source of what sets humans apart from the animals. Creativity, emotion, perception, language, imagination-all have strong connections to the workings of the cortex.

Beginning in the late 19th century, researchers began cataloging variations in the thickness and structure of the cerebral cortex. Korbinian Brodmann, a German neuroscientist, created a numbered map of the cortex in 1906, based on the organizational architecture of the cells that he observed after staining them. He numbered 52 sites in the brain, now called Brodmann areas. While the significance of these areas has been widely debated, further investigation has linked some of the sites to particular functions of the brain. PET scans and functional MRI scans have linked specific motor and sensory functions to specific cortical areas called domains. Brodmann areas 1, 2, and 3, for example, reside right behind the central sulcus and are closely linked to the primary somatosensory cortex, while Brodmann areas 41, 42, and 43 are associated with hearing.

The map is not a precise atlas with domains neatly separated by boundary lines, the way countries are separated by political divisions inked on paper. Many functions such as language and memory overlap domains and may in fact be scattered throughout much of the brain.

IS IT POSSIBLE to have handwriting like a serial killer’s? Does a physician’s scrawl indicate a love for humanity? Much like the phrenologists who thought a bumpy skull could reveal insights into the human psyche, so do today’s graphologists, or handwriting experts, believe that penmanship can tell us a great deal about who we are. Handwriting analysts have succeeded more than phrenologists in selling their pseudoscience. Witness the TV ads in 2008 that analyzed car buyers’ signatures. Proponents claim that because the brain controls psychological traits and muscles that produce handwriting, they must be linked. No causal link has been found. Graphologists lack scientific rigor, often analyzing the writing of people with known traits-kind of like shooting an arrow at a barn, then drawing a bull’s-eye around it.

Nor is the map an indicator of destiny, as other scientists would find. In the early 19th century, Franz Joseph Gall made his own maps of the brain and skull, but they proved faulty. He examined the bumps on the head and drew erroneous conclusions about the functions of the underlying portions of the brain. Physical variations in the size and shape of the head have nothing to do with the workings of the brain power beneath. Damage to a particular Brodmann area, however, may manifest itself in predictable ways, such as language deficiencies resulting from lesions in areas 44 and 45.

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