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a 15 percent increase in the number of brain nerve cells. You know that in children, intensive
education accompanied by strong nurturing and healthy social stimulation often leads to outstanding
academic and subsequent professional success. It is as if these enviromental factors are the cognitive
enhancers, the promemory agents, of childhood. But can a similar approach be used to boost memory
in older people, whose nerve cells have largely lost the ability to reproduce?

Substances that stimulate the growth and branching of existing nerve cells, without necessarily
increasing their number through a reproductive process, may enhance cognitive abilities. For
example, infusing a naturally occurring substance called nerve growth factor into mice increases
neuronal branching and improves connectivity among brain cells. These ideas are still in animal
experimentation, but clinical trials are likely to begin with one or more neurotrophic compounds in
the near future.

Pluripotent Nerve Cells: A Neuroscience Controversy

A healthy diet, regular exercise, and intellectual and social stimulation are clearly beneficial to brain
function. There is a molecular basis to the effects of these types of environmental stimulation in the
brain. Although most nerve cells in an older person's brain have indeed lost the ability to reproduce,
there are a few primitive cells, called pluripotent cells, that retain the capacity to differentiate or
evolve into several types of nerve cells at any time during the life span, including old age. While
these cells are small in number, they can still play an important restorative role after injury or
damage or the aging process itself. Some of these pluripotent neural cells appear to be present in the
hippocampus, and stimulating them to differentiate and reproduce may prove to be an excellent
promemory strategy. As a matter of fact, a few drug companies are trying to develop neurotrophic
compounds that can stimulate these primitive, pluripotent cells to differentiate and grow into
functioning nerve cells in the brain.

Basic research on pluripotent nerve cells has been very limited, and some scientists question if
they even exist in the adult human brain.

Transplantation

A more direct human application is transplantation, which has been tried with dopamine-producing
cells in Parkinson's patients who suffer