Roger Wolcott Sperry

Introduction

Roger Wolcott Sperry (20 August 1913 – 17 April 1994) was an American neuropsychologist and neurobiologist who reshaped how science thinks about the two halves of the brain. Working with patients whose corpus callosum had been surgically cut to control severe epilepsy, he showed that the left and right cerebral hemispheres are not interchangeable and can each carry on perception, learning and decision-making with a striking degree of independence. For this he received half of the 1981 Nobel Prize in Physiology or Medicine, the other half going to David Hubel and Torsten Wiesel for their work on the visual system.

Sperry spent his career on two questions he wrote in the front of a freshman psychology notebook: Where does behaviour come from? What is the purpose of consciousness? The first led him to the chemoaffinity hypothesis of neural wiring; the second to a theory of mind as an emergent, causally effective property of the living brain.

Early Life and Education

Sperry was born in Hartford, Connecticut, to Francis Bushnell Sperry, a banker, and Florence Kraemer Sperry. His father died when Roger was eleven, and his mother supported the family as an assistant to the principal of the local high school. He grew up partly on a farm near Hartford, collecting moths as a younger boy and keeping wild animals as pets — interests that prefigured an experimental career spent with fish, frogs, salamanders, rats, cats and monkeys.

At Hall High School in West Hartford he was a multi-sport athlete, setting a state record in the javelin, and won an Amos C. Miller scholarship to Oberlin College. At Oberlin he captained the basketball team and graduated in English literature in 1935, a choice he later explained as a commitment to clear writing. A freshman course in psychology taught by R. H. Stetson, a specialist in the physiology of speech, redirected him; he stayed on for a master's degree in psychology (1937) before moving to the University of Chicago, where he took a PhD in zoology in 1941 under the neuroembryologist Paul A. Weiss.

Academic and Professional Career

Sperry did a postdoctoral year (1941–42) with Karl Lashley at Harvard, then followed Lashley to the Yerkes Laboratories of Primate Biology in Orange Park, Florida, where he worked from 1942 to 1946. During 1942–45 he also fulfilled his military obligation on the Office of Scientific Research and Development's Medical Research Project on Nerve Injuries.

He returned to the University of Chicago as an assistant professor of anatomy in 1946, became associate professor of psychology in 1952, and briefly served as Section Chief of Neurological Diseases and Blindness at the National Institutes of Health. In 1954 Caltech appointed him the inaugural Hixon Professor of Psychobiology; he held that chair until 1984 and remained at the institute as Board of Trustees Professor Emeritus until his death in Pasadena on 17 April 1994.

Major Contributions to Psychology

Chemoaffinity and the hardwired brain

Before Sperry, the prevailing view held that the developing nervous system was a largely equipotential network whose connections were shaped by use, experience and learning. His doctoral supervisor Paul Weiss had implanted a supernumerary limb on a salamander and found that it functioned normally despite being supplied by nerves that did not normally serve a limb.

Sperry's experiments kept pointing the other way. He crossed the motor nerves of a rat's hind limb and found that the animal never learned to lift the leg that had been shocked, continuing for life to lift the other one. He rotated a frog's eye 180 degrees and let the optic nerve regenerate: the fibres grew back to precisely their original targets in the tectum, and the frog thereafter struck to the right for food on its left, permanently. He transplanted belly skin to a frog's back and back skin to its belly, and the animal scratched its belly when its back was touched, forever.

The conclusion, which he called the chemoaffinity hypothesis, was that nerve fibres find their targets by cytochemical matching — that the wiring of the brain is largely specified, not merely trained. Sperry was specific about the form the labels should take: gradients of a small number of molecules across both the projecting and the target tissue, such that two orthogonal gradients could place thousands of axons on a coordinate system without a separate molecular address for each one.

The molecules he predicted were not identified in his lifetime, but the hypothesis made him a pioneer of axonal guidance, a field that now has its molecular identity. Friedrich Bonhoeffer's group, using a membrane-stripe assay that recreated the retinotectal map in a dish, isolated a glycosylphosphatidyl-anchored activity in posterior chick tectum that repelled temporal but not nasal retinal ganglion cells. It was identified in 1995 as ephrin-A2 and ephrin-A5, ligands for the EphA receptor tyrosine kinases. Retinal ganglion cells carry EphA receptors in a rising temporal-to-nasal gradient while the target — the tectum, or the superior colliculus in mammals — carries ephrin-A in the opposite direction. Because Eph-bearing axons are repelled by ephrins, each axon's own receptor level sets how far it can advance before it stops. Misexpressing ephrins in the chick tectum redirects axons to the wrong patches, and in ephrin-A5 knockout mice many fibres overshoot past the superior colliculus into the inferior colliculus while others terminate at topographically incorrect sites. A second set of counter-gradients, EphB and ephrin-B, maps the other axis: forward signalling blocks branches too far in one direction, reverse signalling blocks them too far in the other, and the terminal zone is where the two repulsive forces balance. This is now the standard account of topographic mapping in the vertebrate central nervous system.

Split-brain research

In the 1950s and 1960s Sperry, then his graduate student Ronald Myers, turned to the corpus callosum — the great bundle of fibres connecting the hemispheres, whose function was largely unknown. Sectioning it in cats produced animals that behaved as though they had two independent brains, each able to learn a discrimination the other had not been taught.

A surgical treatment for intractable epilepsy, developed in 1940 by the Rochester neurosurgeon William Van Wagenen, gave Sperry the human equivalent. Working with the neurosurgeon Joseph Bogen and with Michael Gazzaniga, then a graduate student, he tested patients in whom the callosum and anterior commissure had been divided. Because each hemisphere receives input from the opposite visual field and controls the opposite hand, the experimenters could present information to one hemisphere at a time.

The findings were stark. An object shown to the right visual field — and therefore to the left hemisphere — could be named and described. The same object shown to the left visual field could not be named; the patient might insist he had seen nothing, yet his left hand, guided by the right hemisphere, would pick the correct object from a collection. The right hemisphere turned out to be superior at visuospatial tasks, at recognising faces and at drawing, while the left hemisphere retained its dominance for language, calculation and sequential analysis. Sperry concluded that each hemisphere could sustain its own stream of perception, memory and volition.

Consciousness and the mind–brain problem

Sperry drew deliberately large conclusions. He rejected Cartesian dualism but also rejected the reductionism fashionable among his contemporaries, arguing that conscious experience is a supervenient emergent property of neural activity that exerts genuine downward causation on the brain's own physiology. He wrote on the value implications of this position and became, unusually for a neuroscientist of the period, a contributor to journals at the boundary of science and the humanities such as Zygon.

Major Publications

Sperry, R. W. (1945). The problem of central nervous reorganization after nerve regeneration and muscle transposition. Quarterly Review of Biology, 20, 311–369.
Sperry, R. W. (1961). Cerebral organization and behavior. Science, 133, 1749–1757.
Sperry, R. W. (1963). Chemoaffinity in the orderly growth of nerve fiber patterns and connections. Proceedings of the National Academy of Sciences, 50, 703–710.
Sperry, R. W. (1968). Hemisphere deconnection and unity in conscious awareness. American Psychologist, 23, 723–733.
Sperry, R. W. (1981). Recognition of the functional specialization of the cerebral hemispheres (Nobel lecture).

Impact and Legacy

Sperry's awards include election to the National Academy of Sciences (1960), the American Psychological Association's Distinguished Scientific Contribution Award (1971), honorary membership of the Royal Society (1976), the Wolf Prize in Medicine and the Albert Lasker Award (both 1979), the National Medal of Science (1989), and election as a William James Fellow of the American Psychological Society (1990).

His scientific legacy is secure in two directions. The chemoaffinity hypothesis became the founding idea of axon guidance, and the split-brain work established hemispheric specialization as a fact and helped open the modern field of cognitive neuroscience. Neuropsychology still uses the logic of lateralized presentation he developed, and Brenda Milner and others extended the lesion method in ways his work made possible.

The confirmation of chemoaffinity came with a qualification Sperry would have had to take seriously. Molecular gradients turn out to specify the gross architecture of a map and not its fine grain. Reviews of the cadherin and protocadherin literature argue that a strict molecular address code is incompatible with how malleable and robust neural development is, and that activity-dependent remodelling still does much of the fine-scale work. The maps Sperry himself studied can be systematically rewritten — the auditory map of a barn owl shifted by prism goggles, or the eye-specific stripes formed when a third eye is grafted onto a frog — which is difficult to reconcile with wiring fully specified in advance. What survived is the claim he actually made, about graded chemical labels establishing a coarse scaffold; what did not is the stronger reading of the brain as hardwired down to the last connection, a position more often attributed to him than argued by him.

The popular legacy is a different and less flattering story. Sperry's findings were rapidly converted into the left-brain/right-brain myth — the notion that people are either logical or creative depending on which hemisphere dominates, and that education should be rebalanced accordingly. The evidence does not support this, and Sperry himself said so, but the idea outran him, generating a lasting industry of "right-brain" training programmes and personality quizzes. Large-scale neuroimaging analyses have since found no sign that individuals are hemisphere-dominant in any trait-relevant sense.

The deeper claim — that cutting the callosum divides consciousness into two — has also been contested. In the mid-1980s the psychobiologist Jarre Levy of the University of Chicago argued that the hemispheres do not operate as two separate minds but integrate complementary contributions, and that no human activity draws on only one side. A 1998 study by Hommet and Billiard showed that children born without a corpus callosum still transfer information between hemispheres, implying subcortical routes that survive the surgery. Most directly, Yair Pinto and colleagues argued in Brain in 2017 that split-brain patients show divided perception but undivided consciousness; Volz and Gazzaniga replied that the apparent unity is an illusion maintained by external cross-cueing and by the intact subcortical visual system. The exchange has not been settled, and part of the reason is that the split-brain era has effectively ended — better anticonvulsant drugs and partial callosotomies mean few such patients are now available for study.

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References

Sperry, R. W. (1961). Cerebral organization and behavior. Science, 133(3466), 1749-1757.