[FieldTrip] preprocessing procedures for ECoG/iEEG data

[Tim Meehan]

Hello all,

I am a new user of fieldtrip and new to analyzing electrophysiological
data. I have familiarized myself with some basics of preprocessing of EEG
data, but I would like to know if there are special considerations for
dealing with ECoG/iEEG data -- our dataset has recordings from both
subdural surface electrodes and depth electrodes, sampled at 2kHz. We are
initially most interested in extracting the high-gamma band (70-150 Hz)
envelope as a measure of local activity.

First a general question: is there anyone who could point me to or provide
me with a preprocessing procedure in fieldtrip that is tailored for
ECoG/iEEG? I've perused the ECoG section in the wiki but there is no
information on preprocessing there.

If this is too vague, some specific questions I have are:
1) What cutoffs do people tend to use for low and high-pass filters?

2) What is your choice for re-referencing, if any? Our initial
reference/ground are the left and right mastoids. I have seen papers that
re-reference to the nearest neighbor. I think I need to use
ft_apply_montage to do this, but beyond that I could use some guidance.

3) At what point do you epoch into trials? My guess is after high/low-pass
filtering and re-referencing but before artifact detection and removal?

Any feedback on these would be very much appreciated. If you need more
details please let me know.

Thanks!
Tim
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