Dear List,
I have tried to find the optimal HRF for my group of subjects to improve the signal and minimise non-specific 'activations'. For that purpose, I have followed Jack Grinband's protocol explained in message #021347 (thanks for such a detailed explanation -hopefully it would be copied below).
If I've done it correctly, I end up with a single custom HRF (one column in a txt file), which I include for each EV by setting "Convolution: Optimal/custom basis functions".
My concern is that now I cannot add the temporal derivative to the model, and I'm wondering whether I should include any kind of slice timing correction, something I didn't do before, or I should be fine. My TR=1.62 s.
On the other hand, I have a group of subjects who take a placebo and later, in a different visit, a drug. I'm interested in comparing brain activation under both conditions. I have calculated the optimal HRF for each visit, that is, one for placebo and one for drug. Is this correct, or should I use the one from placebo for both visits?
Thank you very much,
Javier
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