Hello!

I need a help for setting covariates for the second level analysis.
The experiment was conducted like this;
Group 1 (took real medicine)     : baseline and 1 year after the first visit
Group 2 (control, took palcebo) : baseline and 1 year after the first visit


I want to compare the see-based or ROI-to-ROI analysis result in four ways.
(i) difference between baseline and 1-year follow up in Group 1
(ii) difference between baseline and 1-year follow up in Group 2
(iii) difference between Group 1 and Group 2 in baseline
(iv) difference between Group 1 and Group 2 in follow up

Covariates that need to be controlled for the analysis are age and sex.
For example, I put age of all participants as an order of pre-medication G1, pre-medication G2, post-medication G1, and post-medication G2 into one covariate named 'age'. ('age' = [70.1 73.2 85.3 95.6 .... ])
Group information was also entered as covariates.
For example, 'pre-medication G1' = [1 1 1 1 1......1 0 0 0 0 0 0 0 0 0 0.... 0 0 0 0]

My question is..
- How should I put covariates to properly conduct the four analysis that I want to do? Do I have to make several different versions of them depending on analysis?
- Is it okay to use un-centered values for covariates to do those four analysis that I want to?
- How should I select covariates and contrast in the second level analysis?