Dear Vladimir,
 
Thank you for your answer, you're right that predicted and observed scalp maps match at that time point, it's just that in the region there is negative activation and source activation is shown high positive activation, and it's quite a sharp peak lasting for very short time in that source time course and it is hard for me to interpret that activation, as it's at 100ms poststimulus and in the averaged time series and this activated source is in the inferior frontal cortex, when I would only expect occipital activation? Another thing is that in ERP literature it's quite usual to find direct reference from active electrodes to the brain area activated, e.g. occipital electrodes will be indicating occipital cortex involvment...? Thank you.
 
Regards,
Antanas

From: Vladimir Litvak <[log in to unmask]>
To: [log in to unmask]
Sent: Thursday, 27 August, 2009 11:30:13
Subject: Re: [SPM] imaging source reconstruction

Dear Antanas,

The relation between where the source is and where the electrodes
record the maximal deflection is not a simple one (you can play with
the tool from ftp://www.besa.de/be/besa.de/free_tools/DipoleSimulator-2009-03-27-Install.exe
to get some intuition). Did you try to compare in the rendering tool
the predicted and the observed scalp maps? If they match then perhaps
SPM does a good job after all. If not then I can look at the example
and tell you if there is something wrong. Also remember that SPM does
not reconstruct each time frame separately (like some other packages)
but looks at temporal and spatial modes computed over the whole time
window.

Best,

Vladimir

On Thu, Aug 27, 2009 at 10:21 AM, Spokas
Antanas<[log in to unmask]> wrote:
> Dear Vladimir,
>
> I've incounted troubles with imaging source reconstruction, I've just
> noticed, that at some point in time series, it's estimated source with
> highest activation over the whole brain in the region, where none of the
> electrodes have recorded much of a potential and completely ignored much
> higher potential at different sight?.. meaning that the whole estimation
> flies out of the window? I've checked again all electrode positions in
> cooregistration, and all looks good there. Could you please explain
> Vladimir, thank you.
>
> Regards,
> Antanas
>
>
>