Difference between Group Average Scout vs. Individual Scouts

Discussions
1

Hello,

I created a User scout using a Group Average head model. When I extract the data from this scout into a matrix_scout file and plot it in Matlab, the trace looks exactly how I saw it on Brainstorm.

However, when I try to pull the individual participants’ matrix_scout files that make up this group and plot the mean trace, it looks very different (even after accounting for differences in y-axis scale). I am looking for insight into what happens in Brainstorm “behind the scenes” when extracting data from a Group Average file vs. averaging the individual participants’ data after extracting their scouts? I would like to use my individual participants’ data to run further analyses and statistics, but I am worried that the averaged data does not match the group scout trace.

Thank you in advance for any guidance!

2

Hi @evansdc0,

There differences will be in how the Scout value is extracted, and how the Source maps for the subjects are averaged. Can you provide mode information on how this aggregation is done, so we can help you to spot on the difference origin.

  1. Is each Subject using their individual's anatomy?
  2. For each Subject, which source space is used? Surface or Volume?
  3. If Surface source space, are sources constrained or unconstrained?
  4. How was the Group average computed? Were sources rectified?