Dear all,

we calculated separate meta-analyses for structural as well as functional abnormalities. After calculating the overlap of both maps, we ran into some difficulties and would like to clarify the interpretation of the results.

SDM creates two different tables: "VBM pos fMRI" and "VBM neg fMRI". Are we right to assume that "neg" refers to smaller structures in our patient sample compared to healthy controls, whereas "pos" refers to bigger structures? And is the same true for the following positive or negative values within a Table: increased or reduced activation?

If yes, this would result in:
neg-Table, pos section - smaller structure in the patient cohort with increased activation in the fMRI analysis
neg-Table, neg section - smaller structure in the patient cohort with reduced activation
pos-Table, pos section - bigger structure in the patient cohort with increased activation
pos-Table, neg section - bigger structure in the patient cohort with reduced activation

What aspects should be considered when deciding which map (VBM or fMRI) to insert first in the analysis?

Thank you very much in advance!

Dear user,

You are right assuming "neg" refers to smaller structures or hypo-activations in your patient sample compared to healthy controls, whereas "pos" refers to bigger structures or hyper-activations.

You can insert fMRI before VBM, results will be the same with the consideration that the "neg" section of the "pos" file will be the "pos" section of the "neg" file and vice versa. To make sure you are not confused between "neg-pos" and "pos-neg" I would suggest looking at the results of the separate meta-analyses (i.e. for VBM and for fMRI).

Best wishes,

Joaquim