UC Berkeley researchers find a unique brain ‘noise’ signature for dream sleep

When people sleep, an electrical “noise” in their brains can reveal whether or not they are dreaming, according to a July 28 study led by campus researchers.

The two basic types of sleep are rapid eye movement, or REM, sleep and non-REM sleep. Using small, metal electrodes attached to the patients’ scalps, the researchers were able to measure their brains’ electrical activity in the shape of rhythmic waves.

While this technique can generally be used to distinguish between wakefulness, non-REM sleep and general anesthesia, the electrical activity of the brain during REM sleep, or dream sleep, is similar to that during wakefulness, according to the study.

“As an anesthesiologist I told my patients every day before surgery that they were about to sleep,” said lead author Dr. Janna Lendner, a campus postdoctoral fellow and an anesthesiology resident at University Hospital Tübingen, in an email. “At some point I realized that I wasn’t sure that this was the truth – was anesthesia like sleep or wasn’t it?”

According to Lendner, non-REM sleep is characterized by strong rhythmic patterns. She added that although most researchers focus on the rhythmic waves in the recordings, most brain activity is not rhythmic.

Lendner’s idea was that the asynchronous, “noisy” brain activity that she observed could also carry information about the underlying brain state, especially for REM sleep.

The study’s finding that the brain’s electrical activity contains a unique signature for REM sleep also has practical implications in a medical setting.

“In a research and clinical setting, this marker makes it possible to distinguish wakefulness from REM sleep, other sleep states and anesthesia,” Lendner said in the email. “It could be used in automatic sleep staging of neuromonitoring during anesthesia or in the intensive care unit.”

Dr. Jack Lin, a study co-author and a neurologist at UC Irvine, agreed that their findings may have important clinical applications in anesthesiology.

Administering medicine based on patients’ heights and weights does not always take into account individual differences in their brains’ sensitivity to anesthesia, Lin added.

“There’s no one-size-fits-all anesthesia protocol when someone is getting surgery,” Lin said.

Lin added that by monitoring the unique signature of REM sleep, however, operating room physicians may be better able to give patients the right amount of anesthesia.

According to Lendner, the researchers will continue to investigate this signature in coma patients to try to learn more about their prognosis, but they are also curious about the underlying physiological basis of their observations.

“We will continue to compare sleep and anesthesia to learn about both of them,” Lendner said in the email. “Who knows, maybe in the future we can design anesthesia in a way that it becomes more like sleep, with all the benefits of a good night of sleep on our mood, health and cognition.”