How to combine ROIs to calculate connectivity?

Dear Brainstorm experts,

Could you tell me how to combine ROIs for connectivity analysis, please? I calculated source connectivity and got several ROIs including BA4L, BA4R, BA6L, and BA6R. Now I would like to combine BA4L and BA6L into one ROI, and BA4R as well as BA6R into another ROI. How can I reduce the 4* 4 matrices into 2* 2 ones?

Thanks,
K

Hello Kate!

First, I would recommend to copy your scouts to a new atlas. To do so, select all your scouts of interest and under the Atlas drop-down, New Atlas sub-menu, click the Copy Selected Scouts.

Now, make sure you are in this Atlas. Select the scouts that you want to merge into a single scout and in the Scout drop-down you should see 'Merge'.

Let me know if my instructions are unclear or if this didn't work for you.

Thank you very much for your recommendation, Jonathan!

Can I solve the problem by manipulating the matrices rather than using a new atlas? Can I directly reduce the 4* 4 matrices to 2* 2 ones? For example, average some elements?

Thanks!

Can I solve the problem by manipulating the matrices rather than using a new atlas? Can I directly reduce the 4* 4 matrices to 2* 2 ones? For example, average some elements?

There is nothing in the interface that would allow you to average specific rows/columns in an existing matrix.
If you want to do this, you have to do by writing a script to manipulate the data structures directly.
https://neuroimage.usc.edu/brainstorm/Tutorials/Scripting

Note that this may give a completely different result than what you would obtain by using directly the merged scouts in the connectivity process options.
These are not linear measures: e.g. coherence(average) is not equivalent to average(coherence).
(this is in general a problem for the computation of connectivity measures between scouts, for which we don't have a clear answer - you can find many posts on the forum about this)