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Hi Maurice Sounds interesting. So everything is fine when you look within 300 ms and 20Hz. This means I guess that you base the inversion computation (i.e. the weights mapping sensors to sources) on just the first 300ms and maybe 0-40Hz ? The key thing is that you should try the statistical contrast (can you specify what you mean by activation) based on this same window. Hopefully if you take your 300ms period when there is no signal and do both computations within the same window there shouldn't be much there. Can you confirm if this is the case ?. Best Gareth -----Original Message----- From: SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]] On Behalf Of Maurice Göldi Sent: 27 April 2015 18:36 To: [log in to unmask] Subject: [SPM] EEG source localization unrealistic activation found Hi SPM experts I am trying to do source localization of my EEG data. Because I am finding unexpected activation I have created synthetic data (using the code provided in the suplementary material in Lopez et al; Algorithmic procedures for Bayesian MEG/EEG source reconstruction in SPM; 2014). What I expect: 1.) Source reconstruction for the synthetic data at the generated frequency and in the time window where it was generated. 2.) No activation (or minimal leakage due to filtering) in time windows where there was no activity generated. 3.) No activation (or minimal leakage due to filtering) in frequency windows where there was no activity generated. What I get: 1.) Nice source reconstruction. 2.) Activation in time windows where there should be no activation at all. This activation looks just like the activation that I generated. 3.) Activation for frequency windows where I did not generate any data. Again the sources found are similar to what I generated. I have generated many different combinations of sources, frequencies and time windows. E.g. I have one 20Hz source (no additional noise added) from 0 to 300 ms. 1.) I find the source when I window 0-300ms and at 20 Hz. 2.) I find nearly the same pattern when I window from 700 to 800ms and 20Hz. (the time window should be far enough away to have minimal leakage) 3.) I again find nearly the same pattern when I have a window at 0-300ms and 6Hz. The magnitude of activity in the 3 different result is always about the same. I have tried different sources, time and frequency windows but always with the same problem. The coregistration seems fine and also the lead field seems ok as far as I can tell. I am using SPM12. I have also generated datasets with multiple trials and multiple conditions. unfortunately these problems do not average out. My questions: Does anybody else have this problem? Are my expectations wrong? What could be the problem? My guess at the moment is that it might be the temporal projector having an unwanted effect. In spm_eeg_inv_result.m on line 98, TTW is computed. In contrast to W it shows activity across the whole epoch (when I window in 700 -800ms for example). I dont understand the theory well enough to definately say if this a problem or not. Perhaps some of you may have an idea on this? Thanks in advance for any input. Cheers Maurice