With resting state fMRI (rs-fMRI) and functional connectivity booming, and an increasing number of fMRIers adding a resting state scan to their otherwise task-based protocols (even if they don't know what they'll do with the data), the question of whether there is an optimal protocol, perhaps even a standard that could be established across multiple centers, seems timely. From my limited investigation it appears that many fMRIers are doing the logical thing: they are using a version of their task-based fMRI experiment for their resting state acquisition. Is that a good, bad or indifferent thing to do?
A recent review from van Dijk et al. (J. Neurophysiol. 103, 297-321, 2010) set out to determine whether parameters such as run duration, temporal resolution (i.e. TR), spatial resolution (voxel size) and a series of processing steps made any appreciable difference to the detection of default mode and attention networks, against a reference network (a set of nodes not expected to have functional connectivity). Their findings can be summarized as follows: