Source activation displayed with relative values

Discussions
1

Hello Francois,
When I display the source with relative values, what does the value mean?

I calculated the ERP waveform for each subject, and then computed the source with constrained source model, z-score with prestimuli baseline, (no need to project to default anatomy, since all subjects use the same template anatomy), and then average across subjects of the RELATIVE values of z-score to get the group average sources, smooth with 8 mm FWHM.

As the attached picture show, the group average source activation displayed with RELATIVE values. Is the negative values represent the N180 sources and the positive values represent the P180 sources? If so, how can I just present the N180 sources?

Thanks.
Ping

QQ??20161003205502.jpg809×992 87.5 KB

2

Hi Ping,

The sign of the source values are ambiguous, they represent mostly the direction of the current with respect with the normal to the cortex at this point.
Please see the source estimation tutorial (and the difference tutorial):
http://neuroimage.usc.edu/brainstorm/Tutorials/SourceEstimation#Sign_of_constrained_maps
http://neuroimage.usc.edu/brainstorm/Tutorials/Difference

Francois