If you used the Session Log button for renaming EEG or ECG/EOG channels during certain periods since 2019, you may end up with datasets that are slightly corrupted, but easily fixed. That button calls the CTF program changeeeginfo, which is bugged in the version of the software we’ve been using since changing the acquisition computer. It has been replaced by the previous version that works, but it wasn’t always and some datasets may have been affected.
The problem is something like the expected number of channels is wrong, and the data thus shifts between channels from trial to trial. This means some non-MEG channel data ends up in MEG channels and look like large artefacts, and there is a jump between each trial/epoch when looking in continuous mode.
To fix the problem, simply rename the res4.bak file to res4, thus overwriting the bugged file created by changeeeginfo with the original res4 file. You could then run changeeeginfo again (with the good version) if you need to rename the EEG channels. Note that EEG channel names can now be saved in the acquisition configuration file so that they don’t have to be renamed after recording. (We couldn’t do it on the old acquisition computer due to a different bug.)