INNER WORKINGS INNER WORKINGS Inner Workings: Discovering the split mind Helen H. Shen Science Writer metric shapes and everyday objects in either the patient’s right or left field of vision. W.J. could readily name images presented in the right half of space, which are processed by Seeing is believing but the results seemed brain was a pretty shocking thing,” says the left hemisphere. However, he reported see- hard to fathom. In 1962, scientists observed Michael Gazzaniga, then a graduate student ing nothing in response to images in the left an epilepsy patient named W.J. as he at- in the laboratory of Roger Sperry at the visual field, processed by the right hemisphere. tempted to complete a seemingly simple task: California Institute of Technology. Together W.J. could, however, use his left hand manipulate a set of painted blocks to match with Sperry and neurologist Joseph Bogen, (controlled by his right hemisphere) to point a specific pattern. Strangely, he could only Gazzaniga published the first study of W.J. to a picture of the image he had seen on the execute the task with his left hand, not his (2), and later filmed some of his experiments. left, supporting the idea that the right hemi- right. This striking phenomenon, later cap- W.J.’s behavior after surgery suggested that sphere was cognizant but largely lacking in tured on film (Movie S1), was one in a series the corpus callosum mediated communication speaking ability. of findings that would influence the course of between the two hemispheres. With that infor- W.J. was the first of a series of split-brain cognitive neuroscience for years after. mation conduit broken, the Sperry laboratory patients that the Sperry laboratory would W.J. had recently undergone surgery to had an unprecedented opportunity to dissect study. Their data provided some of the clearest sever his corpus callosum—aswathofnerve the different roles that the two sides of the evidence then of the functional differences fibers running between the left and right hemi- brain play in consciousness and cognition. between the hemispheres. The test with blocks spheres—to limit the spread of epileptic sei- In the block test, W.J.’srighthand,con- suggested, for example, that the right hemi- zures in his brain. As a result, the 48-year-old trolled by his left hemisphere, appeared in- sphere excelled at visuospatial tasks, compared man’s brain appeared to contain two seem- capableofmatchingasetofblockstoa with the left hemisphere. Other tests bolstered ingly separate minds, each arising in one cere- pattern on a flash card. W.J.’s left hand, con- the theory that in many people, the left bral hemisphere. trolled by the right hemisphere, could execute hemisphere dominated language skills, com- Earlier studies of brain-injured patients had the task with ease, however, even trying to pared with the right hemisphere. suggested that the two hemispheres differed in jump in to help the fumbling right hand. Modern advances in brain imaging have their functions. However, researchers lacked “That was a powerful moment—to see that since allowed neuroscientists to elaborate on the means to cleanly separate and compare the there were two different mental control sys- these ideas and develop a more complete abilities of the two parts. At the time, some tems competing to solve this problem,” says view of how neural circuits work together neuroscientists thought that the corpus cal- Gazzaniga, now a psychologist at the Univer- across both hemispheres. (Sperry went on to losum played a purely mechanical role of sity of California, Santa Barbara. win the 1981 Nobel Prize in Physiology or holding the hemispheres together (1). In other tests, the researchers attempted Medicine for his split-brain research and “The notion that you could split the mind to communicate with each of W.J.’shemi- work on hemisphere specialization.) into two coherent entities all within the same spheres separately. They flashed images of geo- In the popular imagination, the split-brain studies would eventually give rise to depic- tions of the right brain as the creative side and the left brain as the logical side. “It be- came exaggerated and simplified to the point of being incorrect,” says Charles Gross, a cog- nitive neuroscientist and historian of neuro- science at Princeton University. “It’struethat certain cognitive activities tend to use one hemisphere over the other. For almost all cognitive activities, you need both.” From a scientific perspective, however, the work’s enduring influence was to show that aspects of cognition could be linked to spe- cific neural tissues performing specialized computations, indicating a localization of function, says Michael Posner, a cognitive psychologist and emeritus professor at the University of Oregon. “The idea was not new at the time,” he says, “but this was a particularly strong demonstration.”

1 Gazzaniga MS (2014) The split-brain: Rooting consciousness in biology. Proc Natl Acad Sci USA 111:18093–18094. 2 Gazzaniga MS, Bogen JE, Sperry RW (1962) Some functional effects of sectioning the cerebral commissures in man. Proc Natl A front view of the human brain. Image courtesy of Shutterstock/albund. Acad Sci USA 48(10):1765–1769.

www.pnas.org/cgi/doi/10.1073/pnas.1422335112 PNAS | December 23, 2014 | vol. 111 | no. 51 | 18097 Downloaded by guest on September 28, 2021