Hi Beatrice,
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Splitting the files to obtain one file with a subset of the electrodes is not doable with the interface, you’d have to modify the files structures by yourself. However, most pre-processing functions have an option “Sensor types or names” to process only a specific subset of the channels. You can either decide to enter manually the list of the channels to process, or change the type of some of the channels (eg. edit the channel file and set the type of the EX* channels to “EX”)
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You can create a custom montage to apply for instance a common reference to the EEG channels AND a bipolar montage for the EX channels. You’ll be able to display all your channels in the same “time series” windows, whether the EX* channels are set as “EEG” or as another type.
https://neuroimage.usc.edu/brainstorm/Tutorials/MontageEditor -
SSP and ICA are techniques that work only with large arrays of signals (EEG or MEG caps), their goal is to identify the specific spatial patterns of a specific artifact on a sensor array. There techniques are not applicable to isolated electrodes. But on the other hand, if your isolated electrodes are bipolar recordings, you should not have a lot of cardiac artifact visible in there, unless they are on the chest. Do you?
Francois