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Dear Rita You, and others, should be aware that when the microtime onset is changed to the middle slice (which has become the default in SPM12), it is important to adjust your onset vector correspondingly i.e. subtract TR/2 from the onset vector you used when the reference time bin was 1. Best Torben Torben Ellegaard Lund Associate Professor, PhD Center of Functionally Integrative Neuroscience (CFIN) Aarhus University Aarhus University Hospital Building 10G, 5th floor, room 31 Noerrebrogade 44 8000 Aarhus C Denmark Phone: +45 7846 4380 Fax: +45 7846 4400 http://www.cfin.au.dk [log in to unmask] [log in to unmask] > Den 16/06/2015 kl. 00.10 skrev Rita Loiotile <[log in to unmask]>: > >>> If we don't use STC at all, then wouldn't it make more sense to set the microtime onset to the slice that represents t0, in your example (ascending interleaved), slice #2, which is the first slice being acquired? (so that it aligns with the event times). > >> Well, if you don't go with STC at all, then most of the slices are slightly shifted in time. Assuming all the data of a volume to be acquired in the middle of the TR should lead to the least misalignment (- TR/2 for the first slice, ... + TR/2 for the last one, if you sum up the absolute values this is smaller than 0 for the first slice, ... + TR for the last one). > > Sorry for the email onslaught. Has this changed in SPM12? In my case, I have 36 slices acquired in ascending order. I do NOT perform slice timing correction. Like the original poster, I thought that it was best for me to set microtime resolution = 36 and microtime onset = 1. After seeing this post, I re-ran with microtime resolution = 36, microtime onset = 18. However, the former analyses actually gives me substantially more signal.