 |
 |
Dear SPMers, We have questions about how to apply basis functions to an Event Related fMRI experiment that involves different time course. It is a working memory experiment, and one trial consists of : Stimulus Presentation(6 to 14 sec, depending on different subject group) -> Delay(10 sec) -> Probe Presentation & Response(2 sec) -> baseline(16sec). TR is 2 sec, so that one trial has 17 to 21 scans. We have two subject groups and we are to compare the activation during the delay period between the groups. By searching the SPM mailbase, we come up with the following ideas: 1. use $B!H (Bhrf with temporal and dispersion derivatives $B!I (B to model the period of Stimulus Presentation, because this period has different length depending on subject groups. 2. Use $B!H (BGamma function with derivatives $B!I (B to model the delay period. 3. Use $B!H (Bhrf with temporal derivatives $B!I (B to model the Probe Presentation & Response period. Are they correct? Are there any better ways? Second question is about carry-over effects. Our main interest is about the delay period. But if areas active during the delay period are also activated during the Stimulus Presentation period, then this pre-activation would seriously affect the hrf shape of the delay period, so that we would fail to detect activation in these areas. How one could avoid this? Any comments are welcome and we thank you in advance. Satoshi Tanaka Chikashi Michimata, Ph.D Cognitive Psychology Lab. Psychology Department Sophia University 7-1, Kioi-cho, Chiyoda-ku Tokyo 102-8554 Japan [log in to unmask]