A correlation of contrast estimates across subjects does not tell you
if the neural activity is correlated. The contrast value does not tell
you if the response peaks in the same place. In essence, correlation
of contrasts provides no temporal information. On the other hand, PPI
investigates the temporal aspects of how regions are related. The idea
of PPI is to measure how much influence one region has on the response
in another region. I should also point out the new gPPI toolbox
(http://www.nitrc.org/projects/gppi)
Best Regards, Donald McLaren
=================
D.G. McLaren, Ph.D.
Research Fellow, Department of Neurology, Massachusetts General Hospital and
Harvard Medical School
Postdoctoral Research Fellow, GRECC, Bedford VA
Website: http://www.martinos.org/~mclaren
Office: (773) 406-2464
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On Sat, Oct 20, 2012 at 6:21 PM, Chong, Catherine - SJHMC
<[log in to unmask]> wrote:
> Dear Experts,
>
> I am relatively new to FMRI analysis and have a very basic question:
>
> We have two groups in an event-related memory design. Our goal is to evaluate the activation for new versus repeated faces between these two groups. Using a main effects analysis, both groups activate frontal and medial temporal lobe areas for new versus repeated faces.
>
> We are interested in the correlative patterns between hippocampal activation and frontal activation for these two groups.
> What would be the advantage or disadvantage of just extracting the values for the contrast estimates for both of these areas and analyzing the correlation in let’s say SPSS, versus analyzing the data using PPI? Is it just a matter of looking at total activation versus correlation of time courses?
>
> Many thanks,
>
> Cat
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