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Hi Tomas Where you see positive and negative values in the spatial map for a given component, this means that those areas are anticorrelated wrt that component/process - meaning just what it says - when activity/signal goes up in one area, it goes down in the other. Similarly, if two components' timeseries are negatively correlated, similar story. "Competition" is one interpretation - but that's not the only possibility - could also be inhibition, etc. See the RSN literature for a lot more discussion on these points. If you see an ICA map only have positive values, that means wrt this component there is no strong anticorrelation (within this component). If it is all negative, that means the same thing (as you can flip the sign of the spatial map and timecourse and get the same model) - MELODIC tries to avoid this happening, but doesn't always achieve that. Cheers, Steve. On 25 Mar 2014, at 18:37, Tomas Clarke <[log in to unmask]> wrote: > Hi all, > > I have a few questions about the Melodic ICA output. What is the significance of the anti-correlations? What does it mean for two networks to be anti-correlated in the broader sense? If two networks are shown as anti-correlated on a single component map, does that mean they are working in competition with one another? Also, why do certain component maps seem to only have anti-correlated networks (i.e. all blue, no red) or vice versa (i.e all red, no blue)? > > Thank you, > > -- > Tomas Clarke > Center for Functional and Molecular Imaging (CFMI) > Georgetown University Medical Center > Suite LM-14, Preclinical Science Bldg > 3900 Reservoir Road NW > Washington, DC 20057-1488 > (202) 687-7823 --------------------------------------------------------------------------- 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 --------------------------------------------------------------------------- Stop the cultural destruction of Tibet