Roger Walcott Sperry

Roger Walcott Sperry (1913-1994) severed the nerve pathways that link the two cerebral hemispheres in the course of operating on patients with epilepsy and noted perception and cognition were modified. By presenting visual patterns to one side of a fixation point, thus projecting to one hemisphere alone, it was possible to determine the difference in the functions the hemispheres perform. "The left and right hemispheres of the brain are each found to have their own specialized forms of intellect. The left is highly verbal and mathematical, and performs with analytic, symbolic, computer-like, sequential logic. The right, by contrast, is spatial, mute, and performs with a synthetic, spatioperceptual, and mechanical kind of information processing not yet simulatable in computers." The dominance of the left hemisphere had been noted since Broca's time, but Sperry was able to demonstrate the specilization of the right hemisphere, too. This research provided a tremendous spur to laterality research, although the results were frequently over-interpreted in popular books: the specilizations in function were even related to ancient dichotomies such ad yin-yang.

Sperry's earlier work was concerned with another basic question for neuroscience: how do nerves make the appropriate connections in the brain? For this research he took advantage of the fact that the nerves of Amphibia regenerate. Severing the optic nerve of newt resulted in the nerves remaking their original connections. This obtained even when the eye was rotated. "It follows that optic fibers arising from different points of the retina must differ from one another in some way. If the ingrowing optic fibers were indistinguishable from one another, there would be no way in which they could re-establish their different functional connections in an orderly pattern. Each optic fiber must be endowed with some quality, presumably chemical, that makes it as having originated from a particular spot of the retinal field." Similarly, grafting a piece of skin from the thigh onto the shoulder and then stimulating the shoulder produced a scratching response to the thigh. ~ Page 195