When it comes to the brain, side really does matter. The study of hemispheric specialization is based on the idea that the right and left sides of our brains are dedicated to different functions. While popular conceptions of brain function tend to look at the right brain as the artistic side and the left as the logical side, the in-depth picture is considerably more complex.
In general, research has shown that the left hemisphere of the brain tends to handle more verbal tasks, which involve language, writing, logic, and math, while the right hemisphere deals more with spatial tasks, such as music, art, and creativity.
Evidence for hemispheric specialization often arises from studies of patients with brain injuries. For example, individuals with damage to one part of the left hemisphere can develop a syndrome called dyscalculia, the inability to manipulate numbers or understand mathematical concepts.
As early as the 19th century, scientists began to observe patients with brain injuries in order to link brain areas with specific cognitive functions. Paul Broca, a French physician practicing in the mid-1800s, noted that one of his patients suffered from a severe speech deficit for 30 years, leaving him unable to speak despite being able to understand words. In autopsy, Broca noticed that part of the patient’s left hemisphere had been damaged due to a syphilis-induced lesion. His finding was one of the first cases to link language function to the left side of the brain. Later studies by Carl Wernicke showed that in addition to speech production, language comprehension is also dependent on the left side of the brain.
The study of motor and sensory function led to further discoveries in the field of hemispheric specialization. As Canadian neuroscientist Wilder Penfield famously noted, electrical stimulation of the brain areas responsible for movement on one side of the brain caused muscles on the opposite side of the body to contract.
While early research localized functions in the brain, it did not explain how each side of the brain works independently. This changed in the 1960s, thanks to the Nobel-winning split-brain experiments by Roger Sperry and Michael Gazzaniga.
Split-brain research examines patients who have had their corpus callosum surgically removed as a last resort to reduce the severity of epileptic seizures. The corpus callosum is the bundle of neural fibres that connects the right and left hemispheres of the brain. Without it, information cannot travel from one side of the brain to the other, therefore eliminating any communication between hemispheres.
In the study by Sperry and Gazziniga, split-brain patients were asked to watch a screen where words and pictures flashed briefly in either the left or right visual field. Since each side of the eye communicates information to the opposite side of the brain, stimuli in the right visual field are processed by the left side of the brain, and vice versa. The experiment showed that when words or pictures were presented on the right, patients had no trouble naming them since the visual information reached the left hemisphere, responsible for language. However, when stimuli were presented on the left, patients were no longer able to name or describe the exact same stimuli. This was because the visual information went to the right hemisphere, but could not be transferred to the left hemisphere where it could be processed in terms of language.
Research on hemispheric specialization has gained a great deal of attention, both in the scientific community and in popular culture. It has even been picked up by advertisers who promote products like “right-brain diets” or “brain training” equipment, which claim to provide a balanced workout to both sides of the brain. The trouble is, popular media sources usually exaggerate and misrepresent the right-brain left-brain distinction.
One popular myth is that you can be “right-brained” or “left-brained” and that your preference for a particular hemisphere determines your thinking, personality, and even career choices. No evidence has been put forth to support this idea. And while research shows that the cerebral hemispheres are specialized for handling different cognitive tasks, most tasks engage both sides.
The oversimplification of hemispheric specialization in popular media has led to some annoyance in the scientific community. According to Hooper and Teresi, “the duplex house that Sperry built grew into the Kmart of brain science. Today our hairdresser lectures us about the ‘Two Hemispheres of the Brain.’”
