[FieldTrip] preprocessing procedures for ECoG/iEEG data

David Groppe david.m.groppe at gmail.com
Wed Feb 1 02:53:55 CET 2017

Hi Tim,
   Regarding re-referencing, the two most common re-referencing schemes in
iEEG are average reference or bipolar (i.e., contiguous neighbors in a
strip, shaft, or grid):


You can also use a Laplacian for grids or reference against the white
matter signal obtained from depth electrodes:


Each method has it pros and cons.

If you're interested in using a white matter reference, postimplant brain
shift correction, or some electrode visualization functions not available
in FieldTrip, I recommend trying our new MATLAB electrode localization and
visualization toolbox, iELVis:


hope this is helpful,

On Mon, Jan 30, 2017 at 5:10 PM, Tim Meehan <timeehan at gmail.com> wrote:

> 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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