New FieldTrip User Questions

[Allen Ardestani]

Hello,

I just now came across the FieldTrip toolbox and have a few questions - I
apologize in advance if I am misusing this discussion forum or if my
questions are too obvious.  I am working with a very large dataset of
simultaneous LFP, unit, and NIRS signal from macaques for the purpose of
examining time and frequency dynamics of the signals in various cognitive
conditions.  I would like to implement the clustering/bootstrapping
methodology outlined in [Journal of Neuroscience Methods 164 (2007) 177-190]
to identify significant changes in synchronization and phase-locking.



The specific data in question are LFPs recorded while the monkeys perform a
working-memory task, which consists of a 2s visual sample, 20s delay, and
subsequent choice period.  A 20s baseline precedes the sample (t=0), which
is time-locked to the animal's foveation on the visual sample.  TF plots are
computed using Morlet wavelets for each trial, averaged across trials, and
then normalized with respect to the average baseline.  The first question
I'd like to address is: what time-frequency regions exhibit significant
difference between Correct (left plot) and Incorrect (right plot) trials.



cid:image002.jpg at 01CAA0E0.B7CEC3E0 cid:image003.jpg at 01CAA0E0.B7CEC3E0

I have a number of questions about the appropriateness of applying
bootstrapping to our specific dataset:

1)      Because we use wavelets for spectral decomposition (with
frequency-dependent changes in spectral and temporal resolution) is it valid
to simply cluster across different frequencies?

2)      We are interested in comparing different conditions, where each is
computed relative to its own baseline.  Is there anything wrong with using
the baselines of the same dataset for the null distribution as opposed to
using a different set of baseline data?

3)      The data have been recorded at 1KHz, and this oversampling results
in high spatial-frequency noise.  Do I need to do any downsampling/smoothing
before applying the statistics?

4)      For evaluating the relationship between channels, we compute the
phase-locking value (PLV), which has no meaningful single-trial
measuremetnt.  Is there any way to apply statistical analyses directly to
the average TF plots without resorting back to the individual trials?



Thank you in advance for your help!



____________________________________________________________________________
______

Allen Ardestani    Email: aardesta at ucla.edu

Phone: (310) 825-5528

Medical Scientist Training Program

David Geffen School of Medicine at UCLA

Semel Institute for Neuroscience and Human Behavior

760 Westwood Plaza

Los Angeles, CA 90095-1759

USA




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The aim of this list is to facilitate the discussion between users of the FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG and EEG analysis. See also http://listserv.surfnet.nl/archives/fieldtrip.html and http://www.ru.nl/neuroimaging/fieldtrip.
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