Dear Alex,
The default frequency cut-off used by the high-pass filter is 1/128 Hz, so I understand that in your block design the sum of the activation block and of the rest block is >= 128 s. This is pretty unusual to have such low frequency experimental paradigm. If you are sure you want to work with this data, you might consider changing the frequency cut-off using the following command:
spm_get_defaults('stats.fmri.hpf', 150);
Please mind that SPM removes also the signal at the frequency cut-off (as opposed to FSL), so if your block design is e.g. 70s off + 70s on, you should choose a frequency cut-off that is strictly lower than 1/140 Hz, e.g. 1/150 Hz, like in the command above.
Best,
Wiktor Olszowy
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