Quoting [log in to unmask]:
>
>
>
> Hi Jane,
>
> You're quite right. However, spatial ICA programs like fMRLAB and
> GIFT multiply the time courses corresponding to each spatial
> independent component IF the time course has all negative amplitudes.
> This makes perfect sense because the time course modulates the spatial
> weights, whether they are positive or negative AND the fMRI time domain
> signals that are measured do not have negative values. Thus, only the
> spatial weights can be negative or positive and the corresponding time
> course for each must be positive.
>
> That's my understanding. It seems to be verified by what fMRLAB and
> GIFT do with the time courses too.
>
> Thanks
>
> Todd Penney
>
> Quoting Jane Neumann <[log in to unmask]>:
>
>>
>> hi todd,
>>
>> i am by no means an expert in ICA, but isn't it the case that components
>> in ICA can be determined only up to a factor? that is, amplitude and
>> sign of the determined component cannot be determined unambiguously.
>> maybe thinking along those lines helps.
>>
>> cheerio,
>> jane
>>
>>
>> Todd Penney wrote:
>>>
>>>
>>> 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 Penne
>>
>> --
>>
>> ============================================================================
>>
>> Jane Neumann
>>
>> Max Planck Institute for Human Cognitive and Brain Sciences
>> Stephanstrasse 1a
>> D-04103 Leipzig, Germany
>>
>> phone: +49-(0)341-3552-1737
>> email: [log in to unmask]
>> ============================================================================
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