Processing of intensity-induced rhythms is preserved during both NREM and REM sleep and is associated with activity across frontal and parietal cortical regions.
Key Findings
Results
The sleeping brain shows cortical oscillations synchronized to intensity-induced auditory rhythms during both REM and NREM sleep.
A frequency-tagging paradigm with simultaneous EEG and MEG recording was used to investigate auditory rhythm processing during sleep.
Participants were presented with sequences of vocal syllables at a certain frequency with changed sound intensity while asleep and awake.
Cortical activity oscillated periodically at the intensity-changed frequency during both REM and NREM sleep.
Selective enhancement of spectral power at the intensity-changed frequency was observed in the MEG spectrum during sleep stages.
Results
Neural entrainment to intensity-induced rhythm during sleep was weaker than during wakefulness.
Spectral power enhancement at the intensity-changed frequency was observed during REM and NREM sleep, 'although weaker than during wakefulness.'
The frequency-tagging paradigm allowed direct comparison of neural responses across wake and sleep states.
Both EEG and MEG recordings were used simultaneously to capture these differences.
Results
Sleep compared to wakefulness showed increased engagement of the superior frontal gyrus and inferior parietal lobe during rhythm processing.
Increased engagement of the superior frontal gyrus and inferior parietal lobe was found during rhythm processing in sleep compared to wakefulness.
This pattern suggests a 'sleep-dependent enhancement of higher-order temporal organization of rhythmic information.'
The finding implicates frontal and parietal cortical regions as key areas associated with preserved rhythm processing during sleep.
Results
Neural signals at the vocal syllable frequency were stronger during light sleep than during deep sleep and REM sleep.
Across different sleep stages, neural signals at the vocal syllable frequency in light sleep were stronger than those in deep sleep and REM sleep.
There was no significant difference in neural response at the rhythm frequency among the three sleep stages (light, deep, and REM).
This dissociation suggests that processing of the individual syllable rate and the rhythmic grouping rate may have different sensitivities to sleep depth.
Results
No significant difference in neural response at the intensity-induced rhythm frequency was found among light sleep, deep sleep, and REM sleep.
While syllable-frequency responses differed across sleep stages, rhythm-frequency responses did not differ significantly among the three sleep stages.
This finding suggests that the neural mechanism for processing intensity-induced rhythms is similarly preserved across all sleep stages.
The result contrasts with the stage-dependent differences observed at the vocal syllable frequency.
What This Means
This research suggests that the sleeping brain is not entirely 'offline' when it comes to processing sound patterns. Using a technique called frequency-tagging — where brain waves are recorded with both EEG (scalp electrodes) and MEG (magnetic sensors) while people listen to sequences of syllables that vary in loudness — the researchers found that the brain continues to follow rhythmic patterns defined by changes in sound intensity even during sleep. This response was present in all sleep stages, including light sleep, deep sleep, and REM (dreaming) sleep, though it was weaker than when people were awake.
Interestingly, the sleeping brain appears to recruit different brain regions for this rhythm-processing task than the waking brain does. Specifically, areas in the frontal and parietal lobes — regions associated with higher-level cognitive processing — were more active during sleep than during wakefulness when processing these rhythms. This suggests that the sleeping brain may rely on a partially different, and in some ways more effortful, neural strategy to extract rhythmic information from sounds. The study also found that responses to individual syllables (as opposed to the overall rhythm) were stronger in light sleep than in deep sleep or REM sleep, while the response to the rhythm itself remained consistent across all sleep stages.
These findings matter because they reveal that the human brain maintains a capacity for relatively sophisticated auditory processing — including the detection of rhythmic structure — even during unconscious sleep states. This has potential implications for understanding how the brain processes environmental sounds during sleep, and may inform future research on learning, memory consolidation, and even the delivery of auditory information to sleeping individuals.
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Wang Y, Lu L, Ma L, Zou Q, Gao J. (2026). Sleeping brain oscillates with intensity-induced auditory rhythm.. NeuroImage. https://doi.org/10.1016/j.neuroimage.2026.121910