Brain Selectively Filters Sounds While We Sleep to Keep Us Snoozing

According to a new study published in the journal Current Biology our brain does even more to protect our dreams than previously thought, IFLScience.com reports. The team that conducted this study “used electroencephalography (EEG) to measure activity in the auditory cortices of volunteers as they flowed through the various phases of sleep” to take a closer look at how they processed different sounds.

When participants were awake, they were played two different recordings at the same time – one featured normal speech while the other “consisted of nonsensical noises”. The two tracks were processed separately, but simultaneously. That is until participants fell asleep. 

When participants were played the recordings while they were sleeping “the study authors noticed that the brain began to alter the way it processed each stream.” 

During the tonic rapid eye movement – or REM – sleep phase, the processing of the normal speech was amplified in the auditory cortex, “indicating that the brain was selecting these particular sounds as meaningful and therefore paying extra attention to them.” Once sleepers reached the phasic REM phase of sleep, which is normally when dreams occur, the processing of the normal speech began to be suppressed, while the processing of the “nonsensical” track remained unaffected, indicating the normal speech could potentially disturb the participant’s dream, while the other track was just background noise “and therefore not a threat to the integrity of a dream.”