Hi Rajani,
Some of the activations you are seeing, especially in IPL and posterior cingulate/precuneus may be due to greater decrease in activity levels during the performance of the size decision task. There seem to be some areas that show "task-induced deactivation" relative to the brain activities in the resting state across various experimental protocols.
You may find the following papers helpful in order to understand some of the unexpected activations in your data:
Schulman et al. (1997). Common blood flow changes across visual tasks: II. Decreases in cerebral cortex, Journal of Cognitive Neuroscience, 9 (5), 648-663.
Mazoyer, et al. (2001). Cortical networks for working memory and executive functions sustain th conscious resting state i man. Brain Research Bulletin, 54(3), 287-298.
Binder et al. (1999). Conceptual processing during the conscious resting state: A functional MRI study, Journal of Cognitive Neuroscience,11 (1), 80-93.
(The last group also has another paper published in JoCN about this same topic more recently.)
-Yoshiko
--
Yoshiko Yamada, Ph. D
Research Associate
Brain Development Lab
Psychology Department
1227 University of Oregon
Eugene, OR 97403-1227
On Wed, 26 Mar 2008 13:59:41 +0000, "Joseph T. Devlin" <[log in to unmask]> wrote:
> Hi Rajani,
>
> It's difficult to say anything with great confidence about the
> picture without knowing more about your study, but it doesn't look
> unreasonable for a semantic vs size decisions. Other than the
> expected fronto-temporal areas, you're getting some anterior and
> posterior cingulate activation as well as some IPL -- that's normal.
>
> I'm not entirely sure I understood the analysis, though -- is this
> based on a 3rd level RFX (or mixed effects) analysis where the inputs
> are the cope1.feat/ dirs from the fixed-effects 2nd level
> (subject-level) analyses? If you only did a 2nd level analysis and
> included all 1st level runs from each subject, then the activations
> are inflated by artificially increasing the DOFs and decreasing the
> variance (FFX). Also, your choice of a thresholding method will tend
> towards large, spread out activation clusters. Try either using a
> higher z-value for the cluster analysis (3.1 or above) or using a
> voxel-wise FWE method rather than cluster-wise. But regardless, the
> results look plausible.
>
> hope this helps.
>
>
> Joe
>
> ------------------------
> Joseph T. Devlin, Ph. D.
> Dept. of Psychology
> UCL
> Gower Street
> London, WC1E 6BT, UK
> email: [log in to unmask]
>
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