I extracted their maps from the T1 images of the patient and control group using recon-all. Then, I performed the smoothing process. I carried out the statistics for both volume and cortical thickness with mri_glmfit and mri_glmfit-sim. In some regions of the patient group, while the volume decreased, the cortical thickness increased. What could be the reason for this?
Thanks for your help.
Volume is related to both cortical surface area and cortical thickness (although it is not purely the product of the two). So it is possible in your patient group there was a increase in cortical thickness and decrease in surface area.
If you are looking for a more biological answer, you should know that cortical thickness and surface area are genetically distinct components that are thought to be related to different neural processes (Panizzon et al., 2009). SA is related to to tangential neuronal migration and captures the number of mini-columnar units in the cortex (Chenn and Walsh 2003; Rakic 2009), while CT is related to dendritic pruning and propagation (Huttenlocker, 1990).
Thank you Steven;
Is it possible to compare the surface areas between groups using Freesurfer?
Yup! The process is basically the same, except for you may want to use a larger smoothing kernel for surface area as opposed to the one for cortical thickness.
Thank you very much.