Scientists Think They Know Why Some People Sleep Through Anything

New research suggests that the brain reallocates its attention from external sounds to internal bodily signals during REM sleep, which could explain why some people sleep through alarms, storms, or noisy neighbors. Conducted by researchers at the University of Lausanne and the University of Geneva, the study used electroencephalography (EEG) to record the brain activity of 25 healthy adults while they listened to tones and monitored their heartbeats.

The findings revealed that as participants moved from wakefulness into REM sleep, the brain's response to sounds weakened, particularly during phasic REM sleep, while the response to heartbeats remained strong. This shift in attention from external to internal signals could help explain why some individuals remain deeply asleep despite external disturbances.

The researchers developed an "audio-cardio index" to measure the brain's responses to sounds and heartbeats, showing a gradual shift in processing from sounds when awake to heartbeats in deeper REM sleep. While the study does not imply complete deafness to the surroundings, it suggests that the sleeping brain selectively reduces attention to external inputs while maintaining a focus on vital physiological processes.

This insight into the brain's balance between external (exteroception) and internal (interoception) processing may have implications for assessing consciousness in situations where a person cannot respond behaviorally.

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