Dear Experts,

 

I need some advice on my fMRI study below please:

 

I am looking at the effects of delays (2s, 5s, 8s) between 3 groups of subjects (21 in the A group, 19 in the PC group, 27 in the HC group), so I have a 3 (Delays: 2s, 5s, 8s) by 3 (Groups: A, PC, HC) mixed design and I am interested to look at the 3 x 3 interaction effect. I used the flexible factorial model in SPM and found the F test to be significant in 3 clusters. Next, the mean BOLD contrast for these 3 significant clusters were extracted using MARSBAR and a 3 x 3 repeated measures ANOVA followed by posthoc t-tests (correcting for multiple comparisons) at each delay were conducted using SPSS to determine the between group differences at each delay. Age, gender and SES were included as covariates in the SPSS analysis. I am not sure how to include a covariate in the SPM flexible factorial model, can we?

 

I couldn’t include IQ as a covariate in the SPM or SPSS analysis so I showed that the findings remained significant when I analysed a subsample of IQ -matched subjects (19A, 19PC, 18HC) and there were no significant correlations between IQ and brain activation or with task performance.  

 

The reviewer wasn’t happy with my approach but I am not sure what is a better way to analyse this… Please kindly advice.

 

 

 

Many thanks,

 

Lena