Difference between PLV data(A) and (B)

Discussions
1

Hi,
I calculated the PLV (1×N) in two condition and got the each PLV data (PLV(A) and PLV(B)) on the anatomy (like a source data). I want to know the difference between PLV(A) and PLV(B). I put the PLV(A) and PLV(B) into Process2 and selected the Difference>> Difference:A-B. The data processed by these process shows absolute value. I want simply to know the differences showed by + and - not the absolute value.
Could you give me some information?

Thanks

Jun

2

Hi Jun,

By default, the PLV process returns complex values.
When you display the file in Brainstorm as a cortical map, it automatically shows the absolute value: abs(PLV)

But when you compute the difference, it keeps the complex values, therefore (PLV(A) - PLV(B)) is a complex value.
And when you display it on the cortex, same thing as for PLV(A) and PLV(B), it shows the absolute value: abs(PLV(A) - PLV(B))

If you want to subtract two PLV files and display positive and negative values, you should maybe compute abs(PLV(A))-abs(PLV(B)), or (PLV(A)^2-PLV(B)^2).
To do this, select your two files PLV(A) and PLV(B) in Process1, and run “Extract > Measure from complex values”.
Then compute the difference as you did previously.

Cheers,
Francois

3

Hi Francois,

Excellent!! thank you for your quick reply.

Best,
Jun