Salk Institute, LA JOLLA, CALIF. 28-Oct-98

Human Brains Do Sprout New Cells According to New Salk Study

Like bubbles fizzing from fine champagne, it has long been assumed that our supply of brain cells steadily diminishes through our lives, never to be replenished. According to a landmark Salk study, however, new cells are born in human brains, even in mature individuals.

The results, published in the Nov. 1 issue of Nature Medicine, showed that new cells were generated in the brains of terminal cancer patients who had undergone a diagnostic procedure that labels actively dividing cells. Upon the patients' death, their brains were examined for presence of the diagnostic agent BrdU (for bromodeoxyuridine) which attaches to DNA in dividing cells.

"All of the patients showed evidence of recent cell division," said Salk Professor Fred H. Gage, senior author on the study. "It's interesting to note that this was not a particularly young or healthy group of people, so new cell growth may usually be even more prominent than we observed."

Before the current study, new brain cell growth had been found in adult marmoset monkeys, a lower order primate. Efforts to detect new brain cells in Old World monkeys and apes, however, with whom humans share a more recent common ancestor, had failed. The new growth seen in humans took place in the part of the brain called the hippocampus, which has been linked by many physiological studies to learning and memory. "At this point, it's premature to say that the new cells are being used for learning and memory, but given their location in the brain, it seems reasonable to suggest that they likely do," said co-author Daniel A. Peterson, a postdoctoral fellow in Gage's group.

Previous work in Gage's laboratory had shown that mice reared in a stimulating environment, containing toys, exercise apparatus and increased opportunities for social interaction, generated new brain cells at a greater rate than litter mates raised in standard cages. The mice with more cells also performed better on learning and memory tests involving negotiating mazes. "At the time those results were published, people would ask me if it meant that they could literally increase their brain capacity by traveling or taking on new challenges," said Gage. "I had to say we don't know, given that no one had found newborn nerve cells in human brains. And we still don't know for sure, whether these new brain cells are functioning normally, but the current finding brings us an important step closer to thinking that we have more control over our own brain capacity then we ever thought possible previously."