Men lose brain tissue at almost three times the rate of women, curbing their memory, concentration and reasoning power - and perhaps turning them into "grumpy old men" - a researcher says.

"Even in the age range of 18 to 45, you can see a steady decline in the ability to perform such (attention-oriented) tasks in men," Ruben C. Gur, a professor of psychology at the University of Pennsylvania, said Wednesday.Gur said shrinking brains may make men grumpier because some of the tissue loss is in the left frontal region of the brain, which seems to be connected to depression.

"Grumpy old men may be biological," said Gur, who is continuing to study whether there is a connection.

However, one researcher not affiliated with the study said Wednesday that other recent studies contradict Gur's findings on shrinkage.

The findings, which augment earlier research published by Gur and colleagues, are the result of his studies of the brain functions of 24 women and 37 men over the past decade. He measured the brain volume with an MRI machine and studied metabolism rates.

From young adulthood to middle age, men lose 15 percent of their frontal lobe volume, 8.5 percent of temporal lobe, he said. Women, while they have "very mild" shrinkage, lose tissue in neither lobe. For the brain overall, men lose tissue three times faster than women.

Gur found that the most dramatic loss was in men's frontal lobes, which control attention, abstract reasoning, mental flexibility and inhibition of impulses and the temporal lobe governs memory.

Gur theorized that men lose more tissue because they have lower blood flow than women, particularly in the frontal lobe region. To compound matters, women's brain metabolism - the rate at which the brain breaks down sugar - slows while they age, while men's brains keep working at a vigorous pace.

When the sugar breaks down into toxic components, the blood brings in new sugar, but because men have a weaker flow there is more of a chance of a buildup of toxic byproducts, he said.

That may account for the fact that women live about 10 years longer, he said.

Gur's findings on how circulation and metabolism affect tissue loss augment earlier research published in scientific journals.

But Marilyn Albert, associate professor of psychiatry and neurology at Harvard Medical School, said Gur's findings of brain cell loss in the cortex "is contradicted by a lot of recent studies."

"We've also found that men have more shrinkage in brain tissue as they get older but it's not as significant as he reports," she said.

Gur said men may be able to stop tissue loss by picking hobbies that allow them to rest the gray matter they normally use, he said.