Hi,
that's what I mean. At least when I look at it, there are no
values attached to the color scale (as in the attached figure). So
anyway, the question is, have you verified that the product of the
loading and the activation is indeed negative? If the product is
positive, then the mystery is solved.
On Nov 26, 2007, at 1:51 PM, [log in to unmask] wrote:
>
>
> Hi Vince,
>
> To answer your question, I do have a temporal regressor design
> that corresponds to the spike locations, but I have not used it in
> GIFT to do a temporal sort. Is the temporal sort a feature in one
> of the GIFT menus that I am unaware of? I can tell you that at
> each interictal spike identified on the EEG, a canonical
> hemodynamice response function model was implemented as a model for
> the HR following an interictal spike. In the results that I sifted
> through, one component clearly stands out (the one I sent)
> regarding the spatial locations of activation I am expecting.
> However, the corresponding time course is showing BOLD signal
> decreases at the appropriate times, not increases. I am puzzled by
> this. Any advice would be helpful.
>
> Thank you.
>
> Todd Penney
>
> Quoting Vince Calhoun <[log in to unmask]>:
>
>> Hi Todd,
>> It's hard to tell the sign without seeing your model for spikes.
>> Have you tried creating a regressor that corresponds to the spikes
>> and use
>> this to perform a temporal sort in GIFT? Joe, to answer your
>> comment, the
>> sign/factor score is reflected in the time course that is
>> plotted. Seeing
>> both the timecourse and the image give you the sign in the
>> original data.
>>
>> Regards,
>>
>> Vince
>>
>> P.s. This might be best addressed if you e-mail the GIFT listserv
>> ([log in to unmask]).
>>
>>> -----Original Message-----
>>> From: SPM (Statistical Parametric Mapping)
>>> [mailto:[log in to unmask]] On Behalf Of Dien, Joseph
>>> Sent: Friday, November 23, 2007 7:07 PM
>>> To: [log in to unmask]
>>> Subject: Re: [SPM] independent component analysis of fMRI data
>>>
>>> I'm having a little trouble decoding the images due to issues
>>> with the labeling on the scales but one possibility is that
>>> the sign of an activation (or a factor score if using PCA
>>> terminology) is arbitrary. The only thing that has a
>>> meaningful relationship to the original data is the product
>>> of the loading times the activation (factor score). Are the
>>> loadings at the voxels of interest positive or negative?
>>>
>>> Cheers!
>>>
>>> Joe
>>>
>>> -----Original Message-----
>>> From: SPM (Statistical Parametric Mapping) on behalf of Todd Penney
>>> Sent: Fri 11/23/2007 12:55 PM
>>> To: [log in to unmask]
>>> Subject: [SPM] independent component analysis of fMRI data
>>>
>>>
>>>
>>> Hello all,
>>>
>>> I have a question regarding some ICA results I received on
>>> a series
>>> of fMRI images from an epileptic patient who underwent a continuous
>>> EEG-fMRI scan. The patient was scanned for interictal epileptiform
>>> activity that occurred on her EEG.
>>>
>>> I performed spatial ICA and found one component that I am
>>> convinced
>>> is related to the interictal epileptic spikes. The timing of
>>> the BOLD
>>> response corresponds to that of the epileptic spikes and the
>>> activations are occurring in what looks like the temporal lobe (the
>>> patient was diagnosed with right temporal lobe epilepsy). However,
>>> the activations have a positive z-score but the BOLD response is
>>> showing a DECREASE at each of the spike locations in the
>>> spatial brain
>>> maps (shown by the large signal discharges in the attached images).
>>> This is puzzling to me as I am expecting a BOLD signal increase and
>>> positive spatial weights. I have attached two .jpg files
>>> showing the
>>> brain maps of the component. Is it possible that perhaps the BOLD
>>> signals are INCREASING because of the sign ambiguity when doing ICA
>>> and that the spatial weights should be DEACTIVATIONS with the same
>>> z-scores (which means all I have to do is multiply the time
>>> course and
>>> spatial weights by negative 1)? If not, how is it that I am getting
>>> positive spatial weights with a declining BOLD response at
>>> each spike?
>>> These results are output from the GIFT ICA program.
>>>
>>> Thank you.
>>>
>>> Todd Penney
>>
>>
>
>
------------------------------------------------------------------------
--------
Joseph Dien
Assistant Professor of Psychology
Department of Psychology
419 Fraser Hall (by the coke machine)
1415 Jayhawk Blvd
University of Kansas
Lawrence, KS 66045-7556
E-mail: [log in to unmask]
Office: 785-864-9822 (note: no voicemail)
Fax: 785-864-5696
http://people.ku.edu/~jdien/Dien.html
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