A team of researchers from Freiburg investigated how random sounds played during sleep affect the consolidation of new memories. This result shows that untargeted acoustic stimulation disrupts deep sleep. As a result, the slow brain waves characteristic of this sleep phase occur less frequently and spread irregularly throughout the brain. It is precisely these changes that prevent new memories from becoming established.
In recent years, sleep research has focused intensively on the question of whether targeted auditory stimulation during sleep can improve the consolidation of new memories. A Freiburg research team led by neuropsychologists Professor Monika Schoenauer and Dr. Nora Roast has found in a new study that auditory stimulation during sleep can also have undesirable consequences.
Randomly played sounds during sleep disrupt deep sleep and change slow brain wave propagation, which prevents new memories from consolidating. The latter is considered an important component of memory formation, as it significantly facilitates the exchange of information between different regions of the brain. “Our findings show that randomly played sounds can disrupt important processes during sleep. Memory formation is not just about slow brainwaves occurring, but how they propagate throughout the brain, and it is precisely this propagation that is disrupted by sound,” Roast says.
Slower brain waves reach fewer areas of the brain
Twenty adults participated in the study. On two test days, they learned both factual knowledge and a sequence of finger movements, followed by a three-hour afternoon nap. The researchers used electroencephalography (EEG) to record brain activity and sleep stages while they slept. On one test day, participants heard a randomly played sound in the form of a series of small clicks while they slept. On the one hand, he remained silent. After the nap, the researchers assessed how well the participants recalled the information they had learned.
Randomly played sounds did little to reduce total sleep time. Instead, they primarily changed their sleep composition. Participants spent significantly less time in deep sleep and more time in light sleep stages. Additionally, slower brain waves occurred less frequently and reached fewer brain areas. In particular, it was this change in spread that was the deciding factor for the significant drop in memory performance.
At a time when intensive research is currently underway to utilize sleep-based stimulation to improve memory processes and use them therapeutically, our findings demonstrate that potential side effects need to be carefully considered. Even sounds themselves, without melody or verbal content, can influence and disrupt the complex processes underlying sleep physiology and memory formation. ”
Professor Monika Schoenauer, Neuropsychologist
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Reference magazines:
new mexico roast, others. (2026). Random auditory stimulation during sleep disrupts progressive slow-wave and declarative memory. iscience. DOI: 10.1016/j.isci.2026.116601. https://www.cell.com/iscience/fulltext/S2589-0042(26)01976-0
