The Split Brain in Man

Michael S. Gazzaniga was Roger Sperry's graduate student and junior collaborator at Caltech in the early 1960s, and he ran many of the human commissurotomy tests himself, beginning with the first modern patient, the former paratrooper known as W.J. By 1967 he was establishing himself as the experimentalist of the programme and, with this piece, its chief populariser — the role he kept for the next half-century.

The article appeared in Scientific American in August 1967, a general-science magazine with a strong editorial filter but no peer review, written to put the split-brain results before a wide audience. Its job is exposition: how cutting the corpus callosum lets an experimenter show a word or picture to one hemisphere alone, so that the left hemisphere can name what it sees while the mute right hemisphere answers only with the left hand. The division of labour between the hemispheres is the through-line.

This sits as a secondary, popularising account, one step from Gazzaniga's own experimental papers and aimed at readers rather than referees. It is the document that carried split-brain research into public consciousness, and it states, in the magazine's words, the same two-spheres reading that Sperry gave the field the following year and that Gazzaniga's own later work complicated with the interpreter.

Gazzaniga's stake was scientific and career-founding. The split brain was the work his reputation was built on, and a vivid popular account served both the science and the scientist; the piece is advocacy for the paradigm as much as exposition of it, written by the person with the most to gain from its reach.