Time-frequency representation of NREM sleep EEG data locked to inhalation peaks, contrasted with random data segments (averaged z-values across significant electrodes). Contours indicate significant clusters (two-tailed dependent sample t test; P < 0.001, corrected), illustrating enhanced power in the SO_spindle range around inhalation peaks (time = 0). The black line on the left illustrates the mean z-power, averaged over time within the cluster (±SEM across participants). The white waveform represents the inhalation-locked respiratory signal (mean ± SEM across participants). The topography illustrates the statistical results between the electrodes. Credit: Natural communications (2023). DOI: 10.1038/s41467-023-43450-5
How are memories consolidated during sleep? In 2021, researchers led by Dr. Thomas Schreiner, head of the Emmy Noether junior research group in the Department of Psychology at LMU, had already shown that there was a direct relationship between the emergence of certain brain activity patterns linked to sleep and reactivation of memory contents. during sleep. However, it was not yet clear whether these rhythms were orchestrated by a central pacemaker.
So the researchers teamed up with scientists from the Max Planck Institute for Human Development in Berlin and the University of Oxford to reanalyze the data. Their results, published in Natural communications, identified breathing as a potential pacemaker. “That is, our breathing influences how memories are consolidated during sleep,” explains Schreiner.
Learning processes studied in a sleep laboratory
For their study, the researchers showed 120 images to 20 participants over two sessions. All the images were associated with certain words. Afterwards, participants slept for approximately two hours in the sleep laboratory. When they awoke, they were questioned about the associations they had learned. Throughout the learning and sleeping period, their brain activity was recorded using EEG, as well as their breathing.
The researchers discovered that previously learned content was spontaneously reactivated by the sleeping brain in the presence of so-called slow oscillations and sleep spindles (short phases of increased brain activity). “The precision of coupling these sleep-related brain rhythms increases from childhood to adolescence and then declines again with aging,” says Schreiner.
Breathing and brain activity are linked
Since respiratory rate also changes with age, the researchers then analyzed the data against recorded breathing and were able to establish a link between them. “Our results show that our breathing and the emergence of characteristic patterns of slow oscillations and spindles are linked,” says Schreiner. “Although other studies have already linked breathing to cognition during waking, our work clearly shows that breathing is also important for memory processing during sleep.”
Older adults often experience sleep disturbances, breathing problems, and a decline in memory functions. Schreiner plans to further study whether there are any connections between these phenomena and whether interventions, such as the use of CPAP masks, already used to treat sleep apnea, make sense from a cognitive.
More information:
Thomas Schreiner et al, Breathing modulates sleep oscillations and memory reactivation in humans, Natural communications (2023). DOI: 10.1038/s41467-023-43450-5
Provided by Ludwig Maximilian University Munich
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