A research team in Freiburg led by neuropsychologists Prof. Dr. Monika Schönauer and Dr. Nora Roüast has found that random sounds played during sleep can disrupt deep sleep and impair memory formation, even when those sounds carry no melody or meaning.

The study involved twenty adults who learned factual knowledge and finger movement sequences before taking a three-hour afternoon nap. Researchers used electroencephalography (EEG) to record brain activity throughout. On one test day, participants heard randomly played clicking sounds during sleep; on another day, conditions remained silent, allowing the researchers to directly compare how the presence of sound affected sleep and subsequent memory performance.

Results showed that random sounds reduced the time participants spent in deep sleep while increasing lighter sleep stages. Critically, slow brain waves, which are essential for memory formation, occurred less frequently and reached fewer brain regions when sounds were played.

“Our findings show that randomly played sounds can disrupt important processes during sleep. For memory formation, it is not only crucial that slow brain waves occur, but also how they propagate throughout the brain,” the researchers explain.

Prof. Schönauer emphasized caution about environmental noise during sleep: “Even the sounds themselves that have no melody or verbal content can influence and disrupt sleep physiology and the complex processes underlying memory formation.”

Journal: iScience
DOI: 10.1016/j.isci.2026.116601
Article Title: Random auditory stimulation during sleep disturbs traveling slow waves and declarative memory
Authors: Roüast, Nora M., Kumral, Deniz, Gais, Steffen, Schönauer, Monika (2026)