-------- Original Message --------
Subject: Re: Question again
Date: Thu, 23 May 2002 16:05:52 +0100
From: Will Penny <[log in to unmask]>
To: [log in to unmask]
References: <[log in to unmask]>
Andreas Jansen wrote:
> Dear SPMers,
>
> I hope someone can help me with that:
>
> Is it generally possible to correlate cerebellar activation to a
> specific activation in the cerebrum?
>
> Using fMRI, I have scanned 14 subjects. To simplify matters, imagine
> there are (for all subjects) three activated clusters in the cerebrum
> and additionally activation in the cerebellum. From a theoretical (e.g.,
> linguistic) point of view, all cerebral activation clusters can be
> attributed to specific functions. It remains to be answered, how the
> cerebellum fits in this linguistic model.
> If it is possible to correlate the activation in the cerebellum to a
> specific cluster in the cerebellum, one could draw conclusions about the
> role of the cerebellum.
>
> The simplest approach I can imagine is to calculate for all subjects the
> signal strength for each activated cluster and see if there is a
> correlation between the signal strength in a specific cerebral cluster
> and the signal strength in the cerebellum.
>
> Is this a valid approach?
>
Yes, although there are more formal ways of doing this.
Using the VOI button you can extract single representative time series
for each of your regions of interest (1 cerebellar, 3 cortical) - this
uses a more robust algorithm than just picking the time series for
single voxels.
You can then export these to a structural equation
modelling package (such as LISREL from
http://www.ssicentral.com/other/entry.htm) or the SEM toolbox for
SPM (soon to be released by Christian Buechel).
Importantly, however, it only makes scientific sense to
look at *changes* in connectivities that are related to aspects
of the linguistic task.
Given this fact, you may initially therefore just want to
look at psychophysiological interactions (PPIs) - where you
put a representative time series (and it's interaction with the
experimental task of interest) into a GLM and then use SPM
to make inferences about how its impact on other areas is
task-related.
See eg. the PPI paper by Friston et al. in Neuroimage (1997) -
http://www.idealibrary.com/links/doi/10.1006/nimg.1997.0291/pdf
Best wishes,
Will.
> --
>
> Andreas
>
>
>
--
William D. Penny
Wellcome Department of Imaging Neuroscience
University College London
12 Queen Square
London WC1N 3BG
Tel: 020 7833 7478
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 7478
FAX: 020 7813 1420
Email: [log in to unmask]
URL: http://www.fil.ion.ucl.ac.uk/~wpenny/
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