[Eeglablist] ICA on concatenated sleep-stage segments in overnight EEG

[Okabe Satomi]

Dear EEGLAB community,

I would like to ask for your advice regarding the application of ICA to overnight sleep EEG data.

I am currently working with continuous overnight EEG recordings that have been sleep-staged every 30 seconds. The sleep stages are classified into five categories: Wake, NREM1, NREM2, NREM3, and REM. While sleep staging is performed in 30-second units, the EEG data themselves are continuous.

One approach I am considering is to first determine sleep stages, then extract continuous segments belonging to the same sleep stage (for example, REM sleep periods that occur multiple times throughout the night), concatenate these segments, and run ICA separately for each sleep stage. The motivation for this approach is that EEG characteristics differ substantially across sleep stages, and I was concerned that applying ICA to the entire night at once might not yield an effective decomposition. In fact, when I applied ICA to the whole-night data and classified components using ICLabel, the resulting components were dominated by noise.

On the other hand, concatenating sleep-stage-specific segments may introduce discontinuities at the boundaries between segments, leading to abrupt voltage jumps. I am therefore uncertain to what extent such discontinuities may negatively affect ICA decomposition.

At the same time, I am aware that ICA has been applied to data composed of multiple temporally non-contiguous continuous segments in previous studies (e.g. Epoched EEG data in ERP study). This suggests that strict temporal continuity may not be an absolute requirement for ICA. However, I am unsure how important the issue of discontinuities becomes in practice, particularly when concatenating long segments that are temporally distant within an overnight recording.

As additional information, ICA using runica did not converge on my data, so I am currently using Picard. When applying ICA to the entire night, I performed ASR (via Dusk2Dawn) and band-pass filtering at 0.2–40 Hz. I plan to apply the same preprocessing to the sleep-stage-specific data unless there is a strong reason not to do so.

My main questions are as follows:

1. Is it methodologically reasonable to extract and concatenate segments belonging to the same sleep stage across the night and apply ICA to the resulting data?
2. Are the discontinuities introduced by such concatenation likely to pose serious problems for ICA, and if so, are there commonly recommended strategies to mitigate these effects?
3. Given the strong non-stationarity across sleep stages in sleep EEG, would you generally recommend applying ICA to the entire night or performing ICA separately for each sleep stage?

I would greatly appreciate any insights or shared experiences.

Best regards,
Satomi Okabe