[FieldTrip] power line noise reduction

[Belluscio, Beth (NIH/NINDS) [E]]

Hi all-
  I am evaluating power using ft_freqanalysis for resting state data.  
  In the preprocessing step, I indicate to remove power line noise at 60 Hz as follows:

    cfg = [];
cfg.dataset = 'resting.ds';
cfg.channel = {'MEG'};
cfg.continuous = 'yes';
cfg.detrend = 'yes';
cfg.dftfilter = 'yes';
cfg.dftfreq = [60 120];
dataCB24rest = ft_preprocessing(cfg)

  Then I evaluate the power at frequencies from 5 to 100 Hz as follows: 

cfg = [];
cfg.method = 'mtmfft';
cfg.taper = 'hanning';
cfg.foi = 5:5:100;
cfg.tapsmofrq = 4;
cfg.output = 'pow';
freqCB24rest = ft_freqanalysis(cfg, dataCB24rest)

When I visualize the result, I get a VERY large value for the power at 60 Hz in every channel.  For example, see attached.

What am I doing wrong?
Thanks for your help,
Beth.
  

Beth Belluscio MD-PhD
Clinical Fellow
Human Motor Control Section
NINDS, NIH
301-402-3495


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