Re: [Freesurfer] Fwd: Comparing HRF undershoots between conditions

Yes, assuming a shape will give you much more power, at least for the individual subject. doug

On 04/11/2013 02:55 AM, SHAHIN NASR wrote:

Sorry that I keep on asking questions but I want to know if using a model can significantly increase the chance of getting a significant response. As far as I see for the positive peak, when I use a model (e.g. gamma model or spmhrf), I see a more significant response compared to when I use the FIR model. Is it correct? If true, then the same might be correct for the negative peak.

P.S.: To be more clear, I am talking about the response maps relative to the baseline.

On Apr 10, 2013 6:46 PM, "Douglas N Greve" <greve@nmr.mgh.harvard.edu mailto:greve@nmr.mgh.harvard.edu> wrote:

yes, that is what you want. The only other way that comes to mind
is to model each event type as two event types one delayed
relative to the other. Then model the responseto each as a gamma.
If the delay is right, then the first gamma should model the main
positive response and the second gamma will model the negative
response. both will be independent from the other.

doug

On 04/10/2013 05:00 PM, shahin@nmr.mgh.harvard.edu
<mailto:shahin@nmr.mgh.harvard.edu> wrote:

    I think I figured it out but I want to double check. I am
    generating
    group-average map for my subjects using isxconcat-sess command
    which
    generates ces maps for each time frame. I think these maps are
    what I
    wanted. Right?
        If you still have other solutions that you think may
    generate more
    reliable results, I am eager to know. For instance, is there
    anyway to
    fit a model as we do for spmhrf or fslhrf, but just for the
    negative
    peak?

    Regards

        That's the problem Doug. I have already generated the FIR
        model but how
        can
        I show the sig MAP for one "particulat time point".  What
        are the other
        ways?


        On Wed, Apr 10, 2013 at 4:05 PM, Douglas N Greve
        <greve@nmr.mgh.harvard.edu
        <mailto:greve@nmr.mgh.harvard.edu>>wrote:

            Hi Shahin, there are several ways that you could do
            it. The one that
            immediately comes to mind is to use an FIR and then
            test for a
            difference
            at a particular post stimulus time point.
            doug




            On 04/10/2013 03:54 PM, SHAHIN NASR wrote:

                Hi,
                      I want to generate a map to show the
                significant difference
                between
                HRF undershoot  (negative peak of activity)
                between two conditions
                independent from the positive peak. Is there
                anyway, to generate this
                map?

                P.S.: Please note that I need a map and not a time
                course graph.


                --
                Shahin Nasr

                PhD in Cognitive Neuroscience
                Martinos Imaging Center, MGH
                Harvard Medical School

            --
            Douglas N. Greve, Ph.D.
            MGH-NMR Center
            greve@nmr.mgh.harvard.edu
            <mailto:greve@nmr.mgh.harvard.edu>
            Phone Number: 617-724-2358 <tel:617-724-2358>
            Fax: 617-726-7422 <tel:617-726-7422>

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        --
        Shahin Nasr

        PhD in Cognitive Neuroscience
        Martinos Imaging Center, MGH
        Harvard Medical School



        --
        Shahin Nasr

        PhD in Cognitive Neuroscience
        Martinos Imaging Center, MGH
        Harvard Medical School
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-- 
Douglas N. Greve, Ph.D.
MGH-NMR Center
greve@nmr.mgh.harvard.edu <mailto:greve@nmr.mgh.harvard.edu>
Phone Number: 617-724-2358 <tel:617-724-2358>
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