It appears many parents know more than some professionals about what contributes to bed-wetting - or at least mom and dad trust their instincts.

A recent experiment at Brigham Young University showed that boys who wet the bed are inclined to be heavier sleepers than those who do not. As part of the experiment, parents created noise by walking up and down stairs, but their sons remained asleep."If you had heard the noise they slept through, it would be terrifying," said Michael J. Lambert, a professor of clinical psychology at BYU who supervised the project.

The fact that the boys were hard to arouse suggests that bed-wetting includes a sleep problem in addition to a storage problem, he added.

Although many parents previously believed their children were heavy sleepers and that this might have something to do with their bed-wetting, Lambert said many professionals doubt this. Prior studies on brain activity during sleep showed no difference between those who wet the bed and those who do not, Lambert said.

These studies, Lambert added, showed no difference in the EEG (electroencephalogram) patterns while bed-wetters and non-bed-wet-ters slept, so professionals sometimes assumed sleep patterns had nothing to do with bed-wetting.

"Parents believed their kids were hard to wake up and that their bed-wetting was really a sleep problem and not another problem, such as an emotional disorder, but professionals disagreed."

The research was conducted by graduate student Paul Jenkins.

To test the difficulty of arousing the children, researchers positioned an alarm 6 feet from the boy's head. When the alarm sounded, the child would need to walk to the alarm and shut it off.

If the alarm was not shut off, it would ring for 30 seconds and then ring again louder.

"This improved on standardizing the way kids would be awakened," Lambert said.

However, mysteries remain. Some non-bed-wetters were also hard to arouse, indicating that sleep is not the only factor involved in bed-wetting. Also, some people can learn not to wet the bed so the problem might not be entirely physiological, Lambert said.