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Hi, Christian's semi-travelling right now so I'll take a stab: On 23 Aug 2009, at 11:29, Philipp G. Saemann wrote: > Dear Christian, > > after temporal concatenation group ICA, use of melodic_mix time > courses to derive > individual resting networks and voxelwise comparison of these > between two group we see > robust focal effects between the conditions. Note that for some datasets/questions, using melodic_mix is a little dangerous in this context - see Christian's OHBM abstract on why dual- regression is preferable to back-projection (the latter is what you get in melodic_mix). If you'd like to beta-test the dual-regression approach let me know and we can send you the stuff. > My concern/hypothesis now is that 'simple' lower general network > fluctuation amplitudes in > one of the conditions leads to this (especially as the major nodes > are affected). > > Question: is there a chance to use the melodid_mix file to derive an > amplitude measure for > each subject? E. g. by using FFT power? Or is the melodic_mix file > changed by normalisation > steps that no absolute amplitude information is contained any more? The spatial maps are variance normalised in the core ICA in MELODIC - so _yes_ there is relevant amplitude information in the timecourses. However see the above comments - using the timecourses output by the first stage of dual-regression would be safer than using melodic_mix. Also, in general, the dual-reg script shows how to separate 'shape' from 'shape-and-amplitude' effects in the spatial maps. Cheers. > > Would you have an alternative suggestion on how to define the > average percentage BOLD > fluctuation of a resting network? > > Thanks a lot again! > Philipp > --------------------------------------------------------------------------- Stephen M. Smith, Professor of Biomedical Engineering Associate Director, Oxford University FMRIB Centre FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK +44 (0) 1865 222726 (fax 222717) [log in to unmask] http://www.fmrib.ox.ac.uk/~steve ---------------------------------------------------------------------------