Peter is absolutely right. Your seed doesn't need to show a difference
between tasks to be different in its connectivity.
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 Mon, May 6, 2013 at 4:37 PM, Zeidman, Peter
<[log in to unmask]> wrote:
> Hi Mark - I would vote for yes, provided you have a good prior reason for selecting that region. Region sROI may be equally active in each of your conditions, and thus show no difference in your contrast, but have stronger connectivity / correlation with a target area in one condition over another.
>
> Best,
> Peter.
>
>> -----Original Message-----
>> From: SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]]
>> On Behalf Of Mark
>> Sent: 06 May 2013 04:01
>> To: [log in to unmask]
>> Subject: [SPM] PPI concept
>>
>> Hi,
>>
>> I have a question regarding PPI concept and hope someone could help.
>>
>> PPI analyses reveal brain region (R) which shows different degrees of
>> correlation with the time series of a seed ROI (sROI) during different
>> psychological variable (e.g., cognitive states A and B). If we plot 2
>> regression lines (one for A and the other for B) representing the
>> correlation between sROI and R, their slopes are different.
>>
>> My question is: Should the activity of sROI be different between
>> cognitive states A and B ? Is this a prerequisite if I want to select
>> it as the sROI and extract its time series for PPI analysis? I found
>> many papers first used [A>B] contrast to determine their sROI and then
>> did PPI analysis. If this region is not activated in [A>B] contrast but
>> we have a hypothesis in this region, can I still select it as my sROI
>> for PPI analysis?
>>
>> Thanks.
>
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