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Andy,

Activation and Deactivation of the task is relative to baseline. Thus, I'm
not sure how you can model the deactivation of baseline.

Claiming XB smells like A is more of a psychological or activity of
individual neuron question, not an fMRI question. The best you can say is
the the BOLD response of smell is not significantly different from each
other. You can also say that XB and A activate the same voxels. You can
test the similar by doing a spatial correlation or applying other
similarity metrics using voxels as the individual measures. The first steps
are probably showing that there are no differences between XB and A AND
that both XB and A activate the same areas. If either of these are untrue,
then the BOLD response patterns are different.

On Tue, Dec 2, 2014 at 4:17 AM, Andy Yeung <[log in to unmask]> wrote:

> Dear all,
>
> I would like to ask 2 questions.
>
> The first is how to model and assess deactivation tasks in SPM.
> For example, my baseline is giving heat to the subjects' hands. Then I
> want to examine different tasks of reducing the somatosensory percept of
> temperature. Is this possible and how to model?
>
> The second is how to assess and claim the similarity of activation pattern
> by different tasks.
> For example, I have 3 smells: A, B, XB. A and B are different smells but
> of course both of them activate olfactory cortex. Now I want to show that
> after exposure to smell X, B will smell like A, ie XB = A. Are there ways
> to show that A, B, XB all activate olfactory cortex but from activation
> pattern we can claim XB smells like A?
>
> Best,
> Andy
>