28 April 1998

How Do We Hear When We Sleep?

A truck roars by and we continue to snore. The neighbours' drum 'n' bass doesn't wake us either. But if the baby so much as burps, we're out of bed like a bullet. The ability to discriminate between sounds while sleeping - and to "decide" which ones are worthy of waking up for - is part of a vigilance system located in the frontal lobe of the brain, according to the findings of an undergraduate from John Hopkins University.

Serena Gondek, a 21-year-old junior majoring in biomedical engineering, presented her research to the annual meeting of the American Academy of Neurology in April, the largest gathering of neurologists in the world. Using electrodes implanted directly on the cortexes of five patients undergoing brain surgery, she was able to locate the part of the brain that processes sound during sleep.

"It is controversial how we monitor our environment while we sleep," says John Hopkins' Gregory Krauss, assistant professor of neurology and Gondek's supervisor. "It's a pretty big part of our lives, but sleep is poorly understood.

The main thing Serena did was to show where on the cortex we hear while we sleep. She did a terrific job, particularly in brain mapping."

Previous studies have relied on electrodes attached to a subject's shaved scalp. But the unsqueamish Serena went one better, delving directly into brains through incisions in patients' skulls. She then used special ear plugs to play tone patterns while her subjects slept. The electrodes detected unique activity in the frontal lobe - as distinct from the primary auditory cortex which processes sound during waking.

"At this point," says Gondek, "we can say that this is where it's happening. But it's still very unclear what's going on there, how this processing works." Perhaps some other undergraduate will rise to the challenge.