<div dir="ltr">Hi Vitoria,<div><br></div><div>Thanks for your input.</div><div><br></div><div>Maybe you (or anyone else) could clarify one thing for me. When demeaning and/or detrending, is it better to do on a long continuous block or within individual trials?</div><div><br></div><div>Thanks,</div><div>Tim</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Thu, Feb 2, 2017 at 4:45 AM, Vitória Piai <span dir="ltr"><<a href="mailto:v.piai.research@gmail.com" target="_blank">v.piai.research@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">
Hi Tim, <br>
<br>
The answers to your questions will depend a lot on what you're
planning on doing later. <br>
<br>
For 1), again it depends. If you're mainly interested in high gamma,
it doesn't really matter that much since you'll do spectral
decomposition later on. You could demean the data and not use any
filters (or maybe a low-pass if you want to get some help with
artifact rejection). <br>
<br>
For 2) here some more recent references that may help. The bottom
line is, as David said, all methods have prons and cons. Choose
wisely depending on what you want to be able to claim about your
data!<br>
Mercier, M. R., Bickel, S., Megevand, P., Groppe, D. M., Schroeder,
C. E., Mehta, A. D., & Lado, F. A. (2017). Evaluation of
cortical local field potential diffusion in stereotactic
electro-encephalography recordings: a glimpse on white matter
signal. NeuroImage, 147, 219–232. <br>
Arnulfo, G., Hirvonen, J., Nobili, L., Palva, S., & Palva, J. M.
(2015). Phase and amplitude correlations in resting-state activity
in human stereotactical EEG recordings. NeuroImage, 112, 114–127.<br>
Shirhatti, V., Borthakur, A., & Ray, S. (2016). Effect of
reference scheme on power and phase of the local field potential.
Neural Computation, 28, 882–913.<br>
Trongnetrpunya, A., Nandi, B., Kang, D., Kocsis, B., Schroeder, C.
E., & Ding, M. (2016). Assessing granger causality in
electrophysiological data: removing the adverse effects of Common
Signals via Bipolar Derivations. Frontiers in Systems Neuroscience,
9: 189.<br>
<br>
Since you're mentioning high gamma, I'm assuming you have stimuli
being presented and you want to look at changes in high gamma as a
function of those. In that case, I guess you have a good idea what
your time windows will be like. So for 3) your suggestion would be a
good way to go. What I usually do is to segment longer chunks of
data than my narrow time windows of interest, mark the artifacts but
do not reject any trials yet. I then save the artifacts and once I
finally settle on what my time windows will be, I exclude trials
with artifacts within that time window. <br>
- ft_databrowser will allow you to mark and save artifacts,
ft_rejectartifact will allow you to remove trials containing the
artifacts. <br>
<br>
<br>
Good luck, <br>
Vitoria<div><div class="h5"><br>
<br>
<br>
<br>
On 1/30/2017 11:10 PM, Tim Meehan wrote:<br>
</div></div><blockquote type="cite"><div><div class="h5">
<div dir="ltr">Hello all,
<div><br>
</div>
<div>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. </div>
<div><br>
</div>
<div>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.</div>
<div><br>
</div>
<div>If this is too vague, some specific questions I have are:</div>
<div>1) What cutoffs do people tend to use for low and high-pass
filters?</div>
<div><br>
</div>
<div>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.</div>
<div><br>
</div>
<div>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?</div>
<div><br>
</div>
<div>Any feedback on these would be very much appreciated. If
you need more details please let me know.</div>
<div><br>
</div>
<div>Thanks!</div>
<div>Tim</div>
</div>
<br>
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