[Marsbar-users] comparability of data from different scanning sessions
Status: Beta
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From: Julia W. <jul...@ru...> - 2008-05-09 13:51:31
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Dear MarsBaR experts, I am a very new user of fMRI and are experiencing some unclarities concerning my data interpretation. Our task required scanning the same subjects twice on two different days using the same task. We conducted three conditions (A,B,C) on the first day and one condition (A2) on the second day. A and A2 were basically the same. The scanner and scanning parameters were the same for the two days. When extracting the time courses using MarsBaR, we experience the following strange phenomenon: Conditions A,B,and C of the first day usually show similar time courses. However, compared to these conditions, condition A2 stays always close to zero. Hence, significant activations in a contrast A2 > B for instance, seem to be due to deactivation in B rather than activation in A2. For the reverse contrast, B>A2, however, there seems to be activation in B and no signal changes in A2. This is the same for a large number of ROIs. The time course for the condition of the second day is always close to zero with respect to the other conditions (although condition A2 of the second day was identical to condition A of the first day). Is it necessary to somehow normalize the data if I want to compare sessions acquired on different days? Or could I be making any other mistake? Any suggestions would be very much appreciated. Regards Julia -- Julia Weiler Ruhr-University Bochum Inst. of Cognitive Neuroscience Department of Neuropsychology GAFO 05/606 Phone: +49-234-3223574 Fax: +49-234-3214622 |