Linear PM -- The BOLD response for the low PM values is either positive or negative and for high PM values would become either negative or positive, respectively. The BOLD response for the task at the mean PM value is 0.

Quadratic PM -- The BOLD response starts out as positive or negative, then decreases or increases as the PM value increases (with the BOLD response being negative or positive, respectively), then increases or decrease as the PM value increases further ending as positive or negative, respectively. The BOLD response for the task is 0 at two PM values, one above and one below the mean PM value. This is the zero crossing of the BOLD response by PM.

I am not sure what tasks or regions would exhibit these effects, but they are theoretically possible.

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, Dec 8, 2014 at 3:04 PM, Aser A <[log in to unmask]> wrote:
Dear Donald and all,

I asked this question a long time ago regarding the possibility of getting significant , for example, 1st order or 2nd order parametric modulation but no significant 0 order (main effect) activation. Donald answered yes!

But up to know I am not sure why and how this is possible ?


Can you help please about describing such results?


Thanks

Aser 

On Thu, Oct 31, 2013 at 8:06 PM, MCLAREN, Donald <[log in to unmask]> wrote:
Yes. It might be a bit hard to explain to a reviewer though.

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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HEALTHCARE INFORMATION and may also be LEGALLY PRIVILEGED and which is
intended only for the use of the individual or entity named above. If the
reader of the e-mail is not the intended recipient or the employee or agent
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On Tue, Sep 24, 2013 at 2:14 AM, fMRI <[log in to unmask]> wrote:
Hi all,

When using parametric modulation up to second order polynomial regression, would it be possible to have significant second order voxels/clusters that are not significant in the zero  order (average) or main regressor   ?

I am concerned about this as I have such of this result!

Regards,

Aser