As brain development goes, "bad" or "inappropriate" experiences are worse than no experiences at all, according to a study in the Jan. 28, 1999, issue of Nature. The study shows that the loss of connections between neurons in the brain is not the result of inactivity, as previously thought, but a consequence of activity that is inappropriate.

Experiences during early postnatal life sculpt the connections between neurons in the brain. Some connections, initially formed early in fetal development, are retained and made stronger, while others are weakened and eventually lost. This refinement of connections is responsible for the acquisition of brain function during infancy. While the mechanisms of experience-dependent brain modification normally are responsible for the improvement of function during development, in some clinical conditions they can actually lead to a loss of function.

For example, a loss of function during infant development can result when one eye is deprived of normal visual experience, as can occur with a cataract. As a consequence of this deprivation, connections serving the eye in the brain are weakened to the point that the eye becomes blind. The blindness is a result of a change in the brain, so it persists even when the cataract is removed.

For some time, the weakening between connections in the brain following "one eye" deprivation was considered a consequence of inactivity in the eye. In fact, the eye remains active even with the eyelids closed. The difference between the open and closed eye is the pattern of activity. The activity generated by a seeing eye is like the signals of a well-tuned radio station. The activity generated by an eye with a cataract, or with the lids closed, is more like static.

Researchers in the Howard Hughes Medical Institute and Department of Neuroscience at Brown
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Contact: Scott Turner
Scott_Turner@Brown.edu
401-863-1862
Brown University
5-Feb-1999