Dear Valeria,,
Negative contrasts could show hypometabolism of group 1 but also hipermetabolism of group 2, since there is no a standard metabolism value at voxel level and what contrast provides is just the sign of the difference between groups. A possible interpretation could be that people worse performing need/demand more resources to perform the task, due to their difficulty of performing it. This could be an alternative point of view in case inhibiton were difficult to justify
Hope this helps
Carles
> El 27 ag 2023, a les 16:04, Valeria Isella <[log in to unmask]> va escriure:
>
> Dear SPMers, I need your help with the interpretation of results of a correlation analysis that I am carrying out between brain metabolism on FDG PET and a cognitive test in a group of patients with dementia
> A higher test score indicates better performance
> When I set the contrast at 0 0 0 +1 (I have age and sex as covariates) I find no significant cluster
> When I set the contrast at 0 0 0 -1 I do find an area of significant (inverse) correlation with the test
> Is this an area of hypometabolism, or hypermetabolism, or some kind of artifact?
> If it’s hypometabolism, it might might make perfect sense from a cognitive viewpoint… precisely, it might indicate reduced metabolism in an area that physiologically inhibits the cognitive function that my test is measuring (therefore patients with more severe hypometabolism in this area obtain a better score on the test)
>
> Is this reasoning correct?
>
> Thanks a lot for your contribution!
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