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Dear Deborah, before concluding that signal in the OFC is being cut off, I'd check that this is indeed the case by overlaying the spm image over the mean EPI image as a template. Magnetic field inhomogenity in that region results in the brain shape in the EPI images to differ from that of the T1 template brains used in displays, sometimes substantially. You might discover that you have no brain where you think the OFC is. This may be especially the case if you are using a 3T scanner. To mask your analysis, choose 'explicit masking' from the menu, after having prepared a 1/0 mask image for selection. Best, Roberto Viviani Quoting Deborah Tang <[log in to unmask]>: > Dear SPM Community, > > While analyzing results from a recent fMRI study, I have discovered > that I have very little activation in the lower regions of the brain. I > am concerned that SPM may have truncated my data in the lower regions > of the brain because they were below threshold. Since I am particularly > interested in activation in the OFC, this is a problem. Upon reviewing > my data (ie. mask.img), it looks like SPM cut out brain activity in the > OFC after first-level analysis. > > To resolve this issue, I am thinking of trying to force SPM to use an > explicit mask of the entire brain. Does anyone know how to implement > this in script format? > > Alternatively, if anyone has better ideas on how to improve signal in > the OFC, please let me know. > > Many thanks in advance for all your help! > Deborah Tang, Doctoral Candidate > McGill University > Montreal Neurological Institute > 3801 University St, Room WB 214D > Montreal, QC H3A 2B4 > Canada > > Phone: (514) 398-6644 Ext. 089469 > Fax: (514) 398-8948 > [log in to unmask]