Aging brains have been found to produce diminished amounts of critical growth factors that spur the birth of new neurons in the brain's learning and memory center.

The find, by researchers at Duke University Medical Center and the Durham Veterans Affairs Medical Center, could mean that drugs enhancing the growth factors might prevent age-related learning and memory declines.

The researchers discovered that levels of three critical growth factors—fibroblast growth factor-2 (FGF-2), insulin-like growth factor -1 (IGF-1) and vascular endothelial growth factor (VEGF) —decline dramatically in the middle-aged hippocampus of rats.

The growth factors are secreted mainly by supporting brain cells called astrocytes. They are critical for enabling stem cells to produce new neurons.

Neuron generation in the hippocampus was known to slow dramatically by middle age in rats equal to 45- or 50-year-old humans, but the molecular basis for this has remained a mystery, according to the researchers.