Hi Bob
> Hi, I'd like to be able to statistically compare the time it takes for the
> event-related response to peak across two regions. So far, I've been using
> rfxplot to extract peri-stimulus time histograms (PSTHs) for the two regions
> I'd like to compare. (rfxplot uses the FIR approach.) I've extracted them in
> 2 sec bins (corresponding to my TR), beginning at stimulus onset and ending
> 10 seconds later (trials last 3-4 seconds). For each subject, is it valid to
> define the time to peak as simply the time bin with the maximum value, and
> to simply use a paired samples t-test to compare the peak time bin across
> subjects?
Perhaps others have more insight, but I don't think there is a
standard way to compare timecourses. I think that the approach you
describe sounds reasonable, except for the fact that comparing timing
of response across different regions is sort of inherently problematic
due to potential differences in neurovascular coupling. If region B
responds later than region A, does that mean that the neural response
in region B happened later? Or could it be that the response happened
at the same time, but blood flow (and thus BOLD) changes had different
timecourses, leading to the apparent difference?
Comparing two conditions in the same region is relatively safe,
because (obviously) the neurovascular coupling is held constant. You
might also be ok showing an interaction, such that the response in
region B is differentially slowed compared to region A for one
condition compared to another. But ultimately region differences are
always going to be confounded with neurovascular differences, so it's
a bit tricky.
The following may be helpful:
Miezin FM, Maccotta L, Ollinger J, Petersen SE, Buckner RL (2000)
Characterizing the hemodynamic response: Effects of presentation rate,
sampling procedure, and the possibility of ordering brain activity
based on relative timing. NeuroImage 11:735-759.
Good luck!
Best regards,
Jonathan
--
Dr. Jonathan Peelle
Department of Neurology
University of Pennsylvania
3 West Gates
3400 Spruce Street
Philadelphia, PA 19104
USA
http://jonathanpeelle.net/
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