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This fMRI study has 4 blocks, each lasting 6 minutes, with 30 volumes (using sparse imaging). In between each block the MRI operator checks in with the participant to ensure they are OK (so, usually less than a minute between blocks). When I specify the first-level model for this in SPM, should I be using 4 sessions (with 30 scans per session), or 1 session (with 120 scans)? I've tried both ways, but when modelling using 4 sessions, I get no significant activation (using default values of p=0.05 and FWE-corrected). So, how do you decide which is more correct for a study such as this: modelling with 4 sessions or 1 session? Thanks.