On Fri, 21 Sep 2007 13:44:25 +0200, Bas Neggers <[log in to unmask]>
>Just a quick series of thoughts:
>when you really intend to regress out BOLD activation caused by NEURAL
>activity driving the movement of the head (which could be due to example
>flexion/extension of nech/shoulder/torso muscles, to mention a few)
>rather than MRI acquisition related signals, you might want to include
>the 2nd derivitive of the parameter describing the relevent movement
>component, and convolve that with the HRF. Many motor areas react
>proportional to the applied force when I remember well, and as most of
>you probably know Newtonion mechanics says that F=m * a, where a is the
>acceleration of a body with mass m.
Yes, you're probably right; second derivative might be better than my
suggestion, which was first derivative.
>However, finding the relevant movent component from the 6 realignment
>parameters would not be that straightforward, since biomechanically the
>muscle force is applied along an angular moment with an axis of rotation
>resembling a line through the back of the head touching the plane
>supporting the head. This axis is also changing with head rotation, to
>complicate things further.
I agree with what you say below:
>To make a long story short: I wouldn't bother about that, unless you are
>really interested in areas where neck/shoulder/etc mucsle motor activity
>As said before, the effects of movement on B0 distortion and
>spin-history artifacts is probably much larger.
>Stephen J. Fromm schreef:
>> On Tue, 18 Sep 2007 15:55:15 +0100, alistair galley
>> <[log in to unmask]> wrote:
>>> dear list,
>>> apologies if this has been covered (i couldnt see it in the 100 or so
>>> movement parameter related messages i surveyed)
>> >from what i gather, including movement movement parameters in the
>>> matrix is a good idea even if you have already
>>> realigned because it can remove additional artifacts not removed by
>>> body transformations, assuming that your movement params
>>> are not correlated with your regressors of interest.
>>> but this only regresses out artifacts, it does not regress out the bold
>>> activity which may be underlying some of the movement.
>>> so i was thinking, wouldnt it make sense to convolve the movement
>>> with the hrf to model some of the underlying neuronal
>>> causes of the movement. obviously the same caveat would apply with
>>> these regressors not being correlated with your
>>> regressors of interest.
>>> does this make sense as something to do and has anyone done this?
>> People do not typically do this, as far as I know. My overall take is
>> that I wouldn't do this, myself.
>> I can't see any reason why it would be a _really bad_ idea, but it's not
>> clear to me that it would help much.
>> As you probably know, the main concern is "regressing out" the effect of
>> motion itself, because the changes in signal it can lead to are
>> Finally, were you to attempt to do what you suggest, you'd have to
>> consider whether you'd really want to convolve the position parameters
>> themselves with the HRF, or something like their first order differences
>> (which would be velocity).
>>> with very best wishes
>Dr. S.F.W. Neggers
>Division of Brain Research
>Rudolf Magnus Institute for Neuroscience
>Utrecht University Medical Center
>Visiting : Heidelberglaan 100, 3584 CX Utrecht
> Room B.01.1.03
>Mail : Huispost A.01.126, P.O. Box 85500
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>Tel : +31 (0)30 2509609 Fax : +31 (0)30 2505443
>E-mail : [log in to unmask]
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