WASHINGTON (AP) _ New neurons are constantly being added to the thinking, learning and memory center of the brain, according to new research that disputes the traditional view that mature brain cells are not replaced when they die.

Elizabeth Gould, head of Princeton University brain research team, said if the research conducted in monkeys can be confirmed in humans, it could lead to news ways to repair brain tissue damaged by injury or diseases such as Alzheimer's.

``This shows that there is a naturally regenerative mechanism'' in the mature brain, said Gould, the first author of a study appearing Friday in the journal Science. ``If we can understand better how it works, maybe we could use that to direct the regeneration and repopulation of neurons in damaged areas of the brain.''

Other brain researchers said that if the Princeton study is confirmed it will reverse the neuroscience dogma that the cortex _ the thinking center of the brain in primates _ is unable to grow new cells or neurons to replace those that wear out.

``This study could be very significant in terms of understanding the range of mechanisms that the cortex has available to it for the storage of information and for repair,'' said William T. Greenough, director of neuroscience at the University of Illinois' Beckman Institute. ``These data scream for a reanalysis of human brain development.''

In the Princeton study, Gould and her team injected monkeys with a compound called bromodeoxyuridine, or BRDU, that is taken up by cells in the process of making new cells.

An examination just hours after the injection showed that the cells in one area of the brain took up the BRDU, proving that they were dividing and making immature neurons.

An examination a week after injection showed that the new neurons had migrated, matured, and, in effect, had plugged themselves into the cortex, the thinking center of the brain.

Just how these new neurons function is not known, said Gould. They could take up existing memories from the old neurons in the cortex, or they could be like a new floppy disk in a computer _ clean and ready to start storing new data. Gould said more research is needed to understand exactly how the brain uses these new cells.