Li, Yu wrote:
> Will:
> Thank you very much for the instruction of how to do PPI. I have some
> questions about it.
> When I press VOI to set up ACC, the center automatically jump to the
> nearest suprathreshold voxel. Then I can't create ROI at the same
> location for different subjects.
I don't think its a good idea to do that anyway.
Its perfectly valid to select the position of the region
based on the functional data. This reflects subject to subject
variation in functional anatomy.
> We would like to put the ROI at the
> coordinate of our choice regardless of whether it is showing
> activation. How can we do that?
>
Don't think you can do that easily.
> Also, can we choose more than one ROI at a time as reference region to
> calculate PPI for each one separately.
>
No - do a separate PPI analysis for each source region.
> What are the regressors PPI.ppi, PPI.P and PPI.Y
>
type help spm_peb_ppi at the matlab command prompt
Best,
Will.
>
> Thanks
>
> Julia Li
> Indiana University Medical Center
> Psychiatry Department
> [log in to unmask]
> (317) 278-1771
>
>
>
> -----Original Message-----
> From: Will Penny [mailto:[log in to unmask]]
> Sent: Tue 4/26/2005 8:57 AM
> To: Anand, Amit
> Cc: [log in to unmask]
> Subject: Re: Correlation of activation
>
>
> Amit Anand wrote:
>
> > Will,
> >
> > What should we use for contrast for this simple correlation
> activation
> > analysis. We have a box-car design with negative and neutral
> pictures. We
> > have put the regressor at the ACC timeseries. if we use a
> contrast 1 -1 1
> > then we do not get any difference from 1 -1. If we do 0 0 1 then
> ACC lights
> > up but so does the rest of the brain.
>
> A t-contrast of [0 0 1] is the correct contrast (assuming ACC is the
> third regressor) to look
> for positive correlations between ACC and other voxels. What
> threshold did you use ?
> eg. p<0.001 uncorrected ? (Note to look for positive or negative
> correlations
> is the F-contrast [0 0 1])
>
> We do not have another psychological
> > variable such as attention so I do not think we can use PPI.
> > Could you tell us what kind of contrast we need to choose to get a
> > meaningful correlation between the ACC time series and other
> regions of the
> > brain which also respond to the negative vs. neutral conditions
> in a box
> > car design.
> >
>
> If you wished to look for voxels that changed their
> correlation with ACC as a function of emotial content, E (defined as
> negative-neutral pictures), then you could do a PPI.
>
> Set up a VOI containing ACC (which I guess you've already done), by
> pressing the VOI button.
>
> Then press the PPI button. Your psychological variable is then
> E (which you can extract using a [1 -1] contrast over the negative
> and neutral picture regressors).
>
> Then set up a new SPM analysis to look for PPIs. Follow the
> instructions here for an example:
>
> http://www.fil.ion.ucl.ac.uk/~wpenny/datasets/attention/README_GLM_PPI.txt
>
> Best,
>
> Will.
>
>
> > Thanks,
> >
> > Amit
> >
> >
>
> --
> William D. Penny
> Wellcome Department of Imaging Neuroscience
> University College London
> 12 Queen Square
> London WC1N 3BG
>
> Tel: 020 7833 7475
> FAX: 020 7813 1420
> Email: [log in to unmask]
> URL: http://www.fil.ion.ucl.ac.uk/~wpenny/
>
--
William D. Penny
Wellcome Department of Imaging Neuroscience
University College London
12 Queen Square
London WC1N 3BG
Tel: 020 7833 7475
FAX: 020 7813 1420
Email: [log in to unmask]
URL: http://www.fil.ion.ucl.ac.uk/~wpenny/
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