I am currently performing some cortical thickness comparisons in my group of subjects and using 

mri_glmfit-sim --glmdir my_dir --cache 2.3010 --cwpalthresh 0.05 --2spaces found some clusters that have significantly different cortical thickness values,

Given Eklund et al PNAS paper, do you suggest I should rather use 

mri_glmfit-sim --glmdir my_dir --sim perm 5000 1.3 perm.pos.13 --sim-sign pos 

in order to convince that the results are not due to false positive?

Thanks

Regards