If you are among those who believe that too many brain cells are a bad thing, you may soon be in the majority.

Recent research at the National Institute of Child Health and Human Development suggests that the body cuts back on the number of brain cells because we generate many more neurons -- cells that carry out the functions of the brain -- than are good for us.

During an early period of rapid cell growth, genetic signals tell neurons to grow and divide wildly.

"This results in a network that's not very functional," said institute neurobiologist Phillip Nelson. "Everything's connected to everything, and you end up with a poorly tuned system."

For the brain to work properly, many of these cells and the connections between them, called synapses, must die off. It is a slow process that begins at birth and usually lasts for six or seven years. Studies have suggested that certain brain abnormalities, such as forms of retardation, result when the brain's ability to prune cells does not work right.

An article in this month's Journal of Cell Biology suggests that scientists are developing a much clearer idea of how the body weeds out excess nerve cells, leaving a tightly knit, functioning brain.

The key, according to the report written by institute scientists, lies not in the neurons but in a different type of brain cell, the glia.

The study indicates that a brain hormone and electrical activity of nerve cells stimulates glia cells to secrete substances that help decide which neurons will live.

"We focused on the role of glia cells," Douglas Brenneman of the institute said. "Because, since they are in the business of keeping neurons happy we thought they might release substances that affect neurons' survival."

They do, though exactly how is still something of a mystery. What scientists do know is that neurons, electrical activity and glia cells appear to team up during human development to carve out a working brain.

In the human brain, the number of synapses is greatest at the time of birth and shortly after.

The pruning process gradually reduces the connections during our youngest years, when human brains generate a lot of electrical activity and absorb enormous amounts of information.

As scientists continue to explore the method by which the brain cuts back on its cells, they hope it will enable them to more fully map the brain's architecture.