SPERRY,ROGER AND HIS CHEMOAFFINITY HYPOTHESIS

In the early 1940s, Roger Sperry performed a series of insightful expe riments on the visual system of lower vertebrates that led him to draw two important conclusions: When optic fibers were severed, the regene rating fibers grew back to their original loci in the midbrain tectum to reestablish a topographical set of connections; and the re-establis hment of these orderly connections underlay the orderly behavior of th e animal. From these conclusions, he inferred that each optic fiber an d each tectal neuron possessed cytochemical labels that uniquely denot ed their neuronal type and position and that optic fibers could utiliz e these labels to selectively navigate to their matching target cell. This inference was subsequently formulated into a general explanation of how neurons form ordered interconnections during development and be came known as the chemoaffinity hypothesis. The origins of this hypoth esis, the controversies that surrounded it for several decades and its eventual acceptance, are discussed in this article. (C) 1998 Elsevier Science Ltd. All rights reserved.