[Eeglablist] Statistics for ERSP and ITC

[Laurent Sheybani]

Dear Eeglabers,

I am working on an EEG dataset of a cognitive task and I would like to see whether there is an increase in power and/or ITC around subjects' answers. Before analysing these data, I am getting used to the EEGLAB gui using epileptic data that I acquired in the past, just to see whether I process my data correctly in eeglab. I marked all interictal epileptic discharges, so that I know when there is an increase in power.

What is very strange is that I find no significant increase in power over the whole window (-2000 to 1000 around interictal epileptic discharges, 3-50 Hz), while the whole window is significant for ITC. I would have expected a significant increase in power around interictal epileptic discharges (as I see it in individual, raw LFP activity) and if there was an increased ITC, I would have expected it to be more specific (in terms of time and frequency range).

The pipeline that I follow is:

  *   Load data into EEGLAB from a .mat file (1x28822528): 1 electrode, 28822528 timeframes at 16000 Hz sampling frequency.
  *   Load the event file
  *   Downsampling the data to new sampling frequency = 100 Hz.
  *   Export epochs of "spike" and "control" period (-2000 to 1000)
  *   Load these .set file into a study (1 subject, 1 session, 2 conditions)
  *   Study design: Categorical variable: condition - Values (control - spike)
  *   Precompute channel measures, selecting ERPs, power spectrum, ERP-image, ERSP and ITC (options for ICA are not chosen, as I have only 1 EEG trace), I keep all default parameters
  *   Plot channels measures:
     *   Stats:
        *   I check "Compute 1st independent variable statistics if any" and "Use single trials for statistics" (I have only 1 subject)
        *   Use EEGLAB statistics, permutation statistics, FDR correction, statistical threshold 0.05
        *   Params: I do not change the parameters.

As you can see (power file: https://urldefense.com/v3/__https://www.dropbox.com/s/rwh3b2u8doc8oab/power.jpg?dl=0__;!!Mih3wA!R-vXecxt4S9nEJwpZ1Y3TT5lFDzVkvCPQW8ctGvZlHkOpF7Adw-hqNe9c3QF6ZzjUvrFqg$ ) (ITC file: https://urldefense.com/v3/__https://www.dropbox.com/s/npa6f7llnv6tbhl/ITC.jpg?dl=0__;!!Mih3wA!R-vXecxt4S9nEJwpZ1Y3TT5lFDzVkvCPQW8ctGvZlHkOpF7Adw-hqNe9c3QF6Zwd2CJ8HA$ ) there is no increase in power, while there is a non-specific change in ITC.

Would any one know where in my processing I did a mistake ? It seems that the ERSP/ITC plots themselves are ok, but the p-values plot are not ?

Thanks in advance for your help !

-----------------------------
Dr. Laurent Sheybani, Ph.D
Médecin interne en Neurologie Clinique
Clinique de Neurologie
Hôpitaux Universitaires de Genève
Rue Gabrielle-Perret-Gentil, 4
1205 Genève
Switzerland