New cells that some parts of the brain keep generating hold the key to learning and memory, experiments on mice conducted at Kyoto University in Japan have shown.
Lead researcher Ryoichiro Kageyama says that the study focused on how genetically altered mice tried to learn and memorise the location of a hiding hole without the help of new brain cells
"It was always unclear whether neurogenesis in the adult was essential for normal brain function, or whether it was an innocent bystander. This shows that it's essential," New Scientist magazine quoted Rodney Rietze of the Queensland Brain Institute in Brisbane, Australia, as saying.
For their study, the researchers created a strain of mice engineered so that when they were given a drug, newly made brain cells in the hippocampus - the brain region essential for learning and memory - produced proteins that killed the cells.
The researchers later looked at how well the mice learned to find a hiding hole, a standard test of learning and memory.
"Usually a mouse remembers the hole after one or two days' training, and will still remember it a week later. These mice took five or six days to remember, and then totally forget it one week later," says Kageyama.
In another experiment, the research team reduced the supply of new cells to the mice's olfactory bulb, the region of the brain that perceives odour.
It was found that the ability of the mice to discriminate between very similar smells was not affected, even though the olfactory bulb shrank.
The mice did not even loose their ability to remember the smells four months later, say the researchers.
The findings indicated new cells might not be as important for smell memory as for spatial memory, they add.
Kageyama, however, points out that the mice's abilities could probably worsen as their olfactory bulbs become more damaged over time, or when new cells in the olfactory bulbs are used for specific types of smell memories not tested in the experiment.
The researchers also engineered mice so that new nerve cells would glow green, and they would be able to test drugs that could be used to stimulate neurogenesis in people, in whom a reduced ability to produce new brain cells may account for age-related memory loss.
"Brain circuitry is not set in stone. It's malleable and growing even in an adult. We've suspected it for a long while, but this is the first evidence that these new cells are doing something functional in learning and memory," says Pankaj Sah of the Queensland Brain Institute in Brisbane.