NeuroImageOct 15, 2020

Linking fast brain waves with sleep spindle rhythms using combined brain recordings

Updated Feb 8, 2026

Abstract

EEG and MEG recordings in 12 healthy humans revealed that low gamma (30-40 Hz) and neighboring beta activity is generally increased during sleep spindles.

There was no consistent coupling of gamma activity to spindle oscillations across time-frequency distributions.
More detailed analyses indicated that low and high gamma power (30-100 Hz) was coupled to the phase of both slow and fast spindles.
Coupling of gamma activity occurred at a fixed phase within individual spindles but varied across different spindles.
Spindles detected only in MEG showed no gamma coupling, suggesting they may represent local spindles of different quality.
Low gamma band power exhibited a ~0.025 Hz infraslow rhythm during sleep, which was faster than the frequency of spindle activity.
The findings propose that spindles may synchronize gamma activity across larger cortical networks, linking local memory processing.

Simplified

Sleep spindles are crucial to memory consolidation. Cortical gamma oscillations (30-100 Hz) are considered to reflect processing of memory in local cortical networks. The temporal and regulatory relationship between spindles and gamma activity might therefore provide clues into how sleep strengthens cortical memory representations. Here, combining EEG with MEG recordings during sleep in healthy humans (n = 12), we investigated the temporal relationships of cortical gamma band activity, always measured by MEG, during fast (12-16 Hz) and slow (8-12 Hz) sleep spindles detected in the EEG or MEG. Time-frequency distributions did not show a consistent coupling of gamma to the spindle oscillation, although activity in the low gamma (30-40 Hz) and neighboring beta range (<30 Hz) was generally increased during spindles. However, more fine-grained analyses of cross-frequency interactions revealed that both low and high gamma power (30-100 Hz) was coupled to the phase of slow and fast EEG spindles, importantly, with this coupling at a fixed phase only for the oscillations within an individual spindle, but with variable phase across spindles. We did not observe any coupling of gamma activity for spindles detected solely in the MEG and not in parallel EEG recordings, raising the possibility that these are more local spindles of different quality. Similar to fast spindle activity, low gamma band power followed a ~0.025 Hz infraslow rhythm during sleep whose frequency, however, was significantly faster than that of spindle activity. Our findings suggest a general function of fast and slow spindles that by spanning larger cortical networks might serve to synchronize gamma band activity occurring in more local but distributed networks. Thereby, spindles might help linking local memory processing between distributed networks.

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Declaration of Competing Interest The authors have no conflicts of interest to declare.

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