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 Stories for April 8, 1998

How Eyes Prepare the Brain for Vision
Competing Signals During Fetal Development Are Critical, Researchers Say

by Robert Sanders, Public Affairs
posted Apr. 8, 1998

Ghost images that continually flit across the retina while we’re still in the womb are critical to setting up the visual system to make sense of the world when we finally open our eyes, according to a definitive new study by Berkeley neuroscientists.

In a report published in the March 27 issue of Science, postdoctoral researcher Anna Penn and Carla Shatz, professor of molecular and cell biology and investigator in the Howard Hughes Medical Institute here, describe the effects of blocking these fleeting images in one or both retinas during early development, before the eyes have opened.

They found that blocking input from one eye disrupts the normal formation of layered structures in a part of the brain that relays signals from the eye to the visual cortex.

This layered pattern shows up in all mammals that have been studied, and thus is apparently crucial to the ability to process visual information.

Competition between signals from both eyes is the key to helping this area of the brain segregate into regions devoted to each eye, the researchers say.

“The balance of activity coming from both eyes is critical to making this pattern needed for binocular vision,” Penn says. “If you block spontaneous retinal activity during this period of development you can adversely affect the pattern.”

The finding is important to understanding how the brain wires itself during development, and how outside influences may interfere with normal development before and after birth.

The ghostly images – waves of activity generated spontaneously by eye cells, without stimulation from light – wash across the retina in random patterns during early development in many if not all mammals.

Shatz and her colleagues discovered this several years ago, and others have found that similar kinds of spontaneous neural activity occur in the developing auditory system and spinal cord, and may be important in preparing the brain to hear a sound or make coordinated movements.

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