Hi helpful listserv
We are having the craziest time with our newest study trying to match our onsets with the hrf.
We have checked the timing on the task (we, the scanner techs, and physicists at our imaging center) and it is 100% correct. All onsets are accurate. Yet when we run our model and look for basic neural activity vs. rest baseline as we have always done, we do not get a large response in occipital cortex, nor do we get motor activity. Yet, if we move the onset timing back 1.5 seconds the motor activity is large and significant - as is activity in the visual cortex. Activity in this model is exactly as I would expect. For reference, this is a memory task where participants look at pictures and make a button response corresponding to their memory decision (something I have done a dozen times before). We have run the model (with the accurate onset convolved with the default hrf in SPM12) on 2 versions of SPM12 and across 3 pilot subjects. The results are always the same whereby moving the onset back 1.5 second provides the most robust neural activity at baseline and captures motor activity).....it is the same every time.
Does anyone have any thoughts? Given that I have no doubt about the onsets, I am thinking that for whatever reason the match with the SPM12 hrf is just not working. (Why I dunno)
I am considering adjusting the format/shape of the hrf in SPM to capture our neural activity and was wondering if anyone has done this before and if you have any advice on how to adjust the spm_hrf script (i.e., a more specific understanding of what changing the variables will do)
Thank you in advance. I am at a complete loss.
-Nancy Dennis
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