Why We “Change Our Minds”

Scientists have known for some time that adult brains continue to create new nerve cells, but the reason for this has never been clear, until a recent study demonstrated that mature brains need this continuous fresh supply in order to sustain functions like smelling and memory.

After researchers at Japan’s Institute for Virus Research in Kyoto University found a way to identify new cells by inserting a fluorescent protein into adult mice, they discovered that–within the course of a year–almost all nerve cells in the olfactory bulbs had been replaced with new ones. The hippocampus, linked to memory and learning, also showed a number of new nerve cells. A second group of adult mice was altered so that their brains were blocked from growing these new nerve cells.

“Normal mice quickly learn which hole to get to where it’s dark and has bedding,” said Ryoichiro Kageyama, director and professor at the university. “For the mutants, they learn where to hide, but after a week, they totally forget, they completely lose their memory.”

These findings are significant for victims of such neurological disorders as Alzheimer’s and Parkinson’s disease, as well as stroke survivors, who may never recover certain faculties because their brains no longer generate new cells.

“In some damaged brains, like after a stroke, there is no neurogenesis (generation of new brain cells),” says Kageyama. “We are interested in knowing where nerve cells come from, and whether we can stimulate neurogenesis.”