Why does the rustle of sheets wake us up on some nights, yet we sleep through the sound of our alarm clocks going off on others? Sleep scientists Scott McKinney of Massachusetts General Hospital in Boston and colleagues used a sophisticated computer program to find out.
The study by McKinney and Ellenbogen implicates tat a type of brain activity known as alpha waves may provide vital clues. With better monitoring of these waves, researchers might be able to develop therapies that could help all of us get a better night's sleep
Our brain activity changes throughout the day. When we're awake, our neurons chatter in short, frequent bursts. Measured on an electroencephalogram (EEG), these "alpha waves" look a lot like earthquake squiggles on a seismograph. When we sleep, our neuron chatter slows down, resulting in less squiggly theta and delta waves. Scientists have shown that alpha waves help us respond to the sights and sounds of our environment. Yet they seem to disappear during sleep, even though we are still able to respond to environmental cues, such as smoke or a passing police siren.
To find out what role these nighttime alpha waves play, McKinney and colleagues recruited 13 healthy subjects to spend several nights in the hospital's sleep lab. When the subjects' EEGs showed that they were sleeping deeply, the researchers played a variety of noises, from a jet engine to an ice machine. The noises started softly, at approximately 40 decibels—about as loud as a quiet home. The researchers gradually increased the noise until the person's EEG spiked, a sign that sleep had been disrupted.
The article concludes that the signal which transcends the boundaries of classical sleep stages, could potentially be used for real-time feedback to novel, adaptive drug delivery systems for inducing sleep.
See full article "Covert Waking Brain Activity Reveals Instantaneous Sleep Depth" in PLoS One.