The brain may explain why people slow down as they get older, starting at age 40. How fast you can throw a ball, run or swerve a steering wheel depends on how speedily brain cells fire off commands to muscles. Fast firing depends on good insulation for your brain's wiring. Now new US research suggests that in middle age, even healthy people begin to lose some of that insulation in a motor-control part of the brain - at the same rate that their speed subtly slows.
That helps explain why "it's hard to be a world-class athlete after
40," concludes Dr George Bartzokis, a neurologist at the University of
California, Los Angeles, who led the work.
And while that may sound depressing, keep reading. The research
points to yet another reason to stay physically and mentally active: An
exercised brain may spot fraying insulation quicker and signal for
repair cells to get to work.
How the new research works
To Bartzokis, the brain is like the Internet. Speedy movement
depends on bandwidth, which in the brain is myelin, a special sheet of
fat that coats nerve fibres. Healthy myelin - good thick insulation wound tightly around those nerve fibres - allows prompt conduction of the electrical signals the brain uses to send commands. Higher-frequency electrical discharges, known as "actional potentials," speed movement - any movement, from a basketball rebound to a finger tap.
Consider someone like Michael Jordan. "The circuitry that made him a
great basketball player was probably myelinated better than most other
mortals," Bartzokis notes. But while myelin builds up during adolescence, when does production slow enough that we fall behind in the race to repair fraying, older
Enter the new research. First, Bartzokis recruited 72 healthy men,
ages 23 to 80, to perform a simple test: How fast they tapped an index
finger. Anyone can do this; it doesn't depend on strength or fitness. Researchers counted how many taps the men made in 10 seconds, recording the two fastest of 10 attempts. Then, brain scans checked for myelin in need of repair in the region that orders a finger to tap.
Strikingly, tapping speed and myelin health both peaked at age 39. Then both gradually declined with increasing age, the researchers reported last month in the journal Neurobiology of Aging.
That doesn't mean the rest of the brain is equally affected. Bartzokis has some evidence that myelin starts to fray a decade or so later in brain regions responsible for cognitive functions - higher-level thinking - than in motor-control areas.
Goal is to fight Alzheimer's disease
So back to his example of Jordan, who last played professionally at
age 40: "Even he started getting older. That circuitry started breaking
down a little," contends Bartzokis. "He can become Michael Jordan the
big-shot businessman ... but not be Michael Jordan the super-duper
basketball player anymore."
Bartzokis is not looking to build a better athlete. His ultimate
goal is to fight Alzheimer's disease. The connection: Building memories
requires high-frequency electrical bursts, too, and Bartzokis' earlier
research suggests an Alzheimer's-linked gene may thwart myelin repair.
But the new research has broader implications because it sheds light
on normal ageing, says Dr Zoe Arvanitakis, a neurologist at Chicago's
Rush University Medical Centre.
"We knew at some age you peak and there's a sense it would
disintegrate as you grow older. But we didn't have a sense of where
that age would be," says Arvanitakis, who next wants to see if myelin
and cognitive functions show a similar trajectory.
Bartzokis' research supports a recent report from German scientists,
that with age comes a weakening of the system that's supposed to repair
broken myelin, adds Dr Bradley Wise of the National Institute on
"Any disruption in these neural circuits and networks will have
problems for functioning," says Wise, who says the two reports are
spurring increased interest into myelin's role in ageing. Until
recently, most myelin research has focused on multiple sclerosis, where
myelin does not gradually degrade but disappears. – (Sapa, November 2008)
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