Hello All, We are analyzing the FreeSurfer volume variables in relation to the delay discounting tasks. We have found statistically significant associations in the expected directions when we use the raw values for the individual regions and the overall cortical and subcortical grey/white matter values. However, we should ideally be using variables that have corrected for total brain size in some way. We have tried this in two ways: calculating a proportionate volume using total gray matter (FS_Total_GM_Vol); and calculating a proportionate volume using intercranial volume (FS_InterCranial_Vol). The issue is that our associations completely disappear, or in some cases, even reverse direction. It seems odd to us that r values would essentially drop to zero when a proportionate volume is used.
We probed this further to see if proportionate volumes were correlated with their corresponding raw value. FS_TotCort_GM_Vol and its proportionate value (i.e., FS_TotCort_GM_Vol / ICV) are correlated r = .030, p = .490. This seems odd to us. For subcortical GM, the correlation is even more confusing, r = -.105, p = .02. When we use total grey matter, the correlations are a bit better, but still not as high as we would expect (.48 for cortical GM and .12 for subcortical GM). Are we missing something here? Are the raw values already adjusted for total brain size in some way and we're essentially doing something redundantly? Any thoughts would be helpful. Michael Amlung ******************************************** Michael Amlung, Ph.D. Assistant Professor Department of Psychiatry and Behavioural Neurosciences DeGroote School of Medicine McMaster University Peter Boris Centre for Addictions Research 100 West 5th Street Hamilton, Ontario L8N 3K7 Canada Telephone: (+1) 905-522-1155, ext. 39014 Email: [email protected] _______________________________________________ HCP-Users mailing list [email protected] http://lists.humanconnectome.org/mailman/listinfo/hcp-users
