[FieldTrip] timelock analysis for source analysis time axis

[Xavier Vrijdag]

Hello Fieldtrip experts,

I am using fieldtrip to do LCMV source analysis. I have a dataset of baseline and 3 exposures to nitrous oxide of which I have 1 minute of EEG recording each. For the analysis I split the 60 second recording into 2 second trials using redefine trial. This creates a struct with the 30 trials and 30 time axis each trial having its own time axis 0:2 2:4 etc.  When calling the timelock analysis for the covariance matrix (with keep trials on) on this dataset I get a struct:
      time: [1×15360 double]
     label: {32×1 cell}
     trial: [55×32×15360 double]
    dimord: 'rpt_chan_time'
       cov: [55×32×32 double]
       cfg: [1×1 struct]

This struct has 1 time axis from 0:60 seconds (fsample=256), with all the trials having their data on the correct time padded with NaNs before and after.

Is this structure useful (keeping the original time axis 0:60) for the source analysis, or is it better to redefine the time axis for all trials to be 0:2? Is there a Fieldtrip function/setting to achieve this? The downside I currently experience is that the data struct is getting very big, causing an out of memory error.

Thank you so much for helping me.

Xavier Vrijdag
PhD student
University of Auckland
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