A new report in the August 10 issue of Current Biology finds that sound sleepers show a distinct pattern of spontaneous brain rhythms.

"We found that by measuring brain waves during sleep, we could learn a lot about how well a person’s brain can block the negative effects of sounds; the more sleep spindles your brain produces, the more likely you’ll stay asleep, even when confronted with noise," said Jeffrey Ellenbogen of Harvard Medical School.

During sleep, brain waves become slow and organized, Ellenbogen explained. Sleep spindles refer to brief bursts of faster-frequency waves. Those bursts of activity are generated by the thalamus, which serves as a way station for most types of sensory information.

"The thalamus is likely preventing sensory information from getting to areas of the brain that perceive and react to sound," Ellenbogen said. "And our data provide evidence that the sleep spindle is a marker of this blockade. More spindles means more stable sleep, even when confronted with noise."

Ellenbogen said he and his colleagues were surprised at the magnitude of the sleep spindle effect. They observed brain patterns of study participants as they slept in the lab for 3 nights. The first night was quiet and the second and third nights were noisy, as the researchers introduced a variety of sounds—a telephone ringing, people talking, hospital-based mechanical sounds, and so on. "The effect of sleep spindles was so pronounced that we could see it even after just a single night," he said.

The researchers say they hope to devise ways to enhance sleep spindles via behavioral techniques, drugs, or devices, but it’s not yet clear how to do that.