Dear vbm experts,
I have a vbm design matrix (multiple regression) that includes age, two independent behavioural scores, and some other covariates of no interest. The orthogonality plot shows relatively low correlation between my three regressors of interest. As I understand it, when I perform a contrast over one of the covariates then this should give me results controlling for all the other covariates (have I oversimplified that?).
In one cluster of voxels I find both a linear effect of age as well as a linear effect of one of my behavioural scores. Moreover, in another region I find a clear quadratic effect of age as well as a linear effect of my second behavioural score. Given the anatomical overlap in these results I wonder whether this can tell me something about the relationship between age and my behavioural scores in terms of the developing brain.
Is the simplest explanation for such results that they show completely independent effects of age and behaviour on grey matter in these parts of the brain? Or is there another way of interpreting such anatomical overlap which I have overlooked?
Many thanks,
Antoinette
|