[FieldTrip] preprocessing procedures for ECoG/iEEG data

Tim Meehan timeehan at gmail.com
Wed Feb 1 16:41:16 CET 2017

Hi David,

Thanks! This should be helpful indeed.


On Tue, Jan 31, 2017 at 8:53 PM, David Groppe <david.m.groppe at gmail.com>

> 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):
> http://www.sciencedirect.com/science/article/pii/S1388245706002616
> You can also use a Laplacian for grids or reference against the white
> matter signal obtained from depth electrodes:
> http://www.sciencedirect.com/science/article/pii/S1053811916304232
> 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:
> http://episurg.pbworks.com
> hope this is helpful,
>       -David
> 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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