The alignment uses the same code as SPM spatial normalisation, so it's
not based on AC-PC but on the whole brain shape.
Vladimir
On Wed, Oct 3, 2012 at 8:58 PM, Jun Wang <[log in to unmask]> wrote:
> thanks, Vladimir. I tried COH,which is worse and showed activation
> everywhere. another related question is the source results are written in
> MNI space by default. how SPM converts from sMRI space to MNI space. SPM
> didn't ask for AC_PC alignment. Just worry about inaccurate alignment might
> affect my source reconstruction.
>
> thanks
> Jun
>
>
> On Wed, Oct 3, 2012 at 2:20 PM, Vladimir Litvak <[log in to unmask]>
> wrote:
>>
>> Dear Jun,
>>
>> First, EEG source localisation is imprecise in general and if you want
>> precise spatial localisation you should rather do fMRI or perhaps
>> dipole fitting. The purpose of EEG source analysis, especially imaging
>> approach is to separate effects taking place in different brain areas.
>> With this said, your result seems quite close to A1 to me, at least
>> much better than many things I've seen myself.
>>
>> Another issue is that the MSP approach uses discrete patches and your
>> solution will be at the nearest patch rather than at the true
>> location. In some cases this can result in some weird looking
>> solutions even for very obvious dipolar scalp patterns. This is a
>> known problem that some people are working to resolve. You can try COH
>> or MMN option which will give you a much less focal solution but the
>> peak could be where you expect.
>>
>> Best,
>>
>> Vladimir
>>
>> On Wed, Oct 3, 2012 at 7:57 PM, Jun Wang <[log in to unmask]> wrote:
>> > Dear Vladimir
>> > This is Jun. I asked you some questions about EEG source
>> > reconstruction
>> > a while ago. but I have to approach you again for some problems which
>> > have
>> > puzzled me for one week. I am trying to do source reconstruction on ERP
>> > N1
>> > for people listening speech sound "ah". What I got is not in primary
>> > auditory cortex. here is what did.
>> >
>> > (1) Coregistration individual polhemus sfp file with individual MRI. the
>> > fiducials(Nas,Lpa,Rpa) are selected by typing the MNI coordinates found
>> > in
>> > individual MRI ( using display images). also using headshape as
>> > recommended
>> > in SPM manual. see F1.jpg
>> > (2) In invert step, choose imaging.
>> > Custom Model with GS inversion.
>> > Time window(80-120ms) this is the significant window got from sensory
>> > statistics.
>> > PST Hanning: NO.
>> > High pass: 1Hz, Low pass:128 Hz.
>> > Source priors: No.
>> > Restrict solutions: No.
>> >
>> > the results model log-evidence is -390.9.
>> >
>> > (3)Source results window:80-120 ms, Frequency of interest: 1-50Hz.
>> >
>> > Finally I got source reconstruction in F2.jpg. The activation in
>> > temporal
>> > cortex is anterior away from primary auditory cortex.
>> >
>> > I want to is there anything I did wrong, why I couldn't get maximum
>> > activation in primary auditory cortex. really appreciate your help.
>> >
>> > thanks
>> >
>> > Jun
>> >
>> >
>
>
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