Hi Alphonso,
I had not go back on this project until now.
I saw your answer so : thank you very much!

Also, you said I was correct about the design.  However, now somebody told me that if I want the correlation between the connectivity difference and pain score difference, I should use [0 1] and not [1 0].
On one hand [0 1]  makes sense to me if it's a correlation, on the other hand [1 0] makes sense if I want subject effect  taking the scores into consideration ...
I must admit, I am a bit confuse.  Could you help me?

Thank you in advance,

Julien.