I want to find out the best Hrf model for orbitofrontal cortex to use for my group of
subjects. I have 16s/32s on/off simple block design. I extracted the timecourse of a TICA
melodic component that showed activation in OFC to use it in the GLM model. Should i
have to change the PP height of the regressor derived from MELODIC to 1 (or same as the
other models i'm comparing). The second model is a 16s square wave convolved with
gamma hrf. Looking at the model it seems that the time to peak is almost 16s. From the
averaged Raw data BOLD plots , it seems that the BOLD peak is more like 6s. Because of
these timing differences the model fit (and therefore PE's and z-scores) would be
less..right?? What parameters in the model setup should i change to bring the peak
forward in time? I tried changing the phase but that shifts the whole waveform forward.
Should i change the square wave block length instead?
Another doubt i have is whether the GLM is more sensitive to height or width of the
response or is it really the overall shape(area under the curve). i.e if i use a 10s square
wave with gamma hrf to model one BOLD response with 1% signal change and duration
of 12 s and a BOLD response with 0.5% signal change with duration of 16s , which will
give me a higher PE value?
Thanks for your patience and time