Research explains why some people can sleep despite noise, focusing on brain choices during sleep. It examines how the brain prioritizes internal signals over external sounds during REM sleep, linked to vivid dreaming. Researchers at the University of Lausanne and the University of Geneva explored brain responses to sounds and heartbeats during wakefulness and REM sleep.

Using electroencephalography (EEG), the study recorded the brain activity of 25 healthy adults. Participants listened to tones while awake and during sleep. The study compared sound responses with heartbeat-triggered responses. Findings show as participants enter REM sleep, brain response to sounds declines, particularly during ‘phasic’ REM sleep, known for vivid dreams. Meanwhile, response to heartbeats stays strong and even enhances.

During sleep, especially in ‘phasic’ REM, the brain focuses more on internal signals over external ones, shifting attention from ‘exteroception’—the processing of external information like sounds—to ‘interoception’—awareness of internal signals such as heartbeat.

The study suggests people who sleep through noise may prioritize internal bodily information over external sounds. The researchers developed an ‘audio-cardio index’ to measure the brain’s shift from sound-focused to heartbeat-focused processing, showing changes in consciousness states.

Sleepers may listen less to surroundings but still process sounds minimally during REM sleep. Findings have broader implications for assessing consciousness, especially under anesthesia or in consciousness disorders. Contact with the research team via email provides further details on the study.