Researchers at the University of Chicago have discovered an important mechanism used by the developing brain to design nerve connections in the section of the brain that interprets visual signals.//

In the process, they have hit upon the first experimental evidence for a decades-old model of how neurons establish distant connections in a way that can consistently relay spatial information.

The research paper is published in the January 5, 2006, issue of the journal Nature.

Here, the researchers show that a gradient of a molecule known as Wnt3 counterbalances another force provided by the EphrinB1-EphB signaling system. The balance between these two signaling systems, they show, is necessary to establish the carefully controlled pattern of nerve connections required to convey spatial information in the correct order from the eye to the brain.

This is the first biological validation of a computational model developed in the early 1980s which suggested that two such forces would be necessary to guide axons as they establish the connections that relay spatial information from one part of the nervous system to another, says Yimin Zou, Ph.D., assistant professor of neurobiology at the University of Chicago and author of the study.

Neurobiologists refer to this type of neuronal connection where the spatial order of neurons of one part of the nervous system is `copied’ onto another—as "topographic mapping." The term describes the creation of a coordinated connection that allows positional information from a grid of sensors, in this case the light-sensitive cells in the retina, to be smoothly and systematically transferred to their target, the structures in the brain that interpret information from the eyes. Without an orderly and faithful connection, information from the eyes could not be properly deciphered by the brain.

Similar topography systems are thought to regulate other sensory systems—such as hearing and tou
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