The good news: as we get older, we become more ambidextrous. The bad news: this new skill develops because the performance of our dominant hand declines so drastically.

Researchers at Ruhr University Bochum in Germany and the California Institute of Technology tested 60 volunteers who described themselves as right-handed. The older the subjects were, the less successful they were at motor performance tests using their dominant hand. Left-hand performance did not deteriorate as drastically with age.

One would think that the dominant hand would resist degeneration better than the other hand, says lead researcher Hubert R. Dinse, a biologist at Ruhr University Bochum. Because the opposite is true, something must cause the decline. Dinse speculates it may come down to simple wear and tear of the hand over time.

In a second experiment that tested hand usage, 36 subjects performed household tasks at home while wearing sensors that detected which hand was in motion at any given time. The sensors indicated that whereas the younger subjects preferred using their dominant hand, the older people used both hands equally—without even knowing it.

“All subjects claimed that they were strict right-handers,” says Dinse, probably because they were used to describing themselves that way and because they continued to write with their right hand.

To tease out why these changes take place, Dinse plans to use imaging techniques to compare how cortical activation in the two brain hemispheres changes with age. Previous research has shown that the left hemisphere, which is responsible for the right hand, is more active in young right-handed adults—so aging could induce either a reduction in left hemisphere activation or an enhancement in the right hemisphere.