[FieldTrip] Time-frequency-analysis for resting state

Pia Michel pia.michel at student.uva.nl
Thu Aug 9 18:38:08 CEST 2018

Hi everyone,

I’m new to both FieldTrip and EEG analysis, and dealing with a somewhat unusual data set, so I’d very much appreciate your help.

We recorded 80s intervals of resting state EEG during a parabolic flight, made up of four 20s intervals of different gravity each. As the gravity shift is gradual and I am interested in the change in alpha and beta power over time, I would prefer not cutting the data into four trials, but analyse it as one trial.

The data is preprocessed and I followed the tutorial for time-frequency analysis for resting state data. I would like to use the first 20s of normal gravity as the baseline, but I don’t know how to use ft_freqbaseline for this. In particular not how I’d do it if I first temporarily redefine the trial into epochs. 

Is the below appropriate for this setting or is there a way to do the freq analysis directly on the entire trial?

How do I define a time window in the first 20s as the baseline to compare the later intervals to?

Thank you so much!

cfg = [];

cfg.length  = 2;

cfg.overlap = 0;

data_segmented = ft_redefinetrial(cfg, data_continuous)

cfg = [];

cfg.method     = 'mtmfft'

cfg.taper      = 'hanning'

cfg.foilim     = [7.5 35];

cfg.keeptrials = 'yes'

freq_segmented = ft_freqanalysis(cfg, data_segmented)

begsample = data_segmented.sampleinfo(:,1);

endsample = data_segmented.sampleinfo(:,2);

time = ((begsample+endsample)/2) / data_segmented.fsample;

freq_continuous           = freq_segmented;

freq_continuous.powspctrm = permute(freq_segmented.powspctrm, [2, 3, 1]);

freq_continuous.dimord    = ‘chan_freq_time',

freq_continuous.time      = time;   


cfg = []

cfg.layout = ‘eeg1010.lay'

ft_multiplotTFR(cfg, freq_continuous);
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