Hi all, I have a few questions on two related topics. Topic 1, conjunction analysis: Thank you Doug for your response pointing out the mergecontrasts tool. I have 2 questions for anyone who may have used this in the past. First, do I specify the two contrasts to merge using the contrast flag twice? Ex: -contrast [name] [thresh] [tail] -contrast [name] [thresh] [tail] or do I specify both contrasts under a single tag? Additionally, this is a memory task and the encoding and retrieval runs were analyzed separately (same analysis type, but same coding in paradigm files and different sessions parent directories) so will it be possible to indicate to the program where the encoding contrast to be merged with the retrieval contrast is? Or will I have to rearrange my directories, recode my paradigm files, and make new contrasts? probably the latter huh?
Topic 2, correlation analysis: As an alternative to a conjunction analysis, is it possible to use freesurfer to perform a voxel-by-voxel group level correlation analysis of encoding versus retrieval runs for a memory task perhaps obtaining a map of r-values or sigs or r values representing the correlation of the time courses from corresponding voxels from the two runs? what freesurfer tools would do this?
Thanks in advance, Cameron
Oh, you want a "conjunction" I think. Corrlation means something else. Try mergecontrasts-sess
doug
Cameron Ellis wrote:
Hi Doug, We would like to compare, voxel by voxel, the activity between two back-to-back runs, one encoding run and one retrieval run for a memory task. Ideally what we have in mind would be to view, on the inflated surface, a map of voxels that were above a certain threshold during both encoding and retrieval. Could we somehow make a whole brain functional mask from the encoding run an apply this to the retrieval run? Cameron
I'm not sure what you are trying to do. sound like you have two values per voxel for each subject that you want to correlate, but you can't really correlate two values. I think I'm missing something ...
doug
Cameron Ellis wrote:
Does anyone have an answer to this question?
Hello,
I am looking for a way to perform voxel-wise, within-subject correlations of two activation maps (in talairach space). The two existing maps reflect encoding and retrieval runs of a memory task. The idea would be to generate a correlation map across all subjects, to identify clusters where there was a positive or negative correlation between encoding and retrieval activation.
I've seen this done with SPM but not Freesurfer. Any suggestions? (Perhaps this would involve glmfit?)
Many thanks, Josh _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
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-- Douglas N. Greve, Ph.D. MGH-NMR Center greve@nmr.mgh.harvard.edu Phone Number: 617-724-2358 Fax: 617-726-7422
In order to help us help you, please follow the steps in: surfer.nmr.mgh.harvard.edu/fswiki/BugReporting