Hi Lars
which surface are you using? If it's the white surface you might try looking at white matter volume to see if it is decreasing
cheers Bruce
On Sat, 6 Sep 2014, Lars M. Rimol wrote:
Hi,
I have performed a longitudinal analysis using the lme module in FreeSurfer, with this model:
intercept(random effect) + centered age + group + group x centered age + sex
I tested the effect of time with this contrast vector [ 0 1 0 0 0 ]. Dependent variable is area.
Here, mapping the second beta means mapping the effect size for (change over) time. In the beta map, I find values from 0 to 0.004. I would interpret that to mean that local area shrinks by at most 0.004 mm² per year in the reference group. But I'm not 100% sure about the biological (or geometrical) meaning of that.
Can I interpret this literally as the mean yearly shrinkage of the three triangles surrounding a given vertex, the average of whose area comprises the area score of the vertex, being 4/1000 mm? Of course, these maps are smoothed with 30mm, so the real spatial resolution is nowhere near this....
Thank you!
-- yours, Lars M. Rimol, PhD St. Olavs Hospital Trondheim, Norway