Additionally, there are continued methodological debates regarding rs-fcMRI data acquisition and processing. Some groups define rest as lying quietly with eyes closed (e.g., Supekar et al. 2009, 2010), some with eyes open, some using fixation blocks extracted from block design studies (e.g., Dosenbach et al. 2006; Fair et al. 2007, 2009), and some using data acquired during task with the task regressed out (Fair et al. 2007; Andrews-Hanna et al. 2007). These various acquisition conditions may affect rs-fcMRI relationships as there are small changes in rs-fcMRI correlations during sleep (Larson-Prior et al. 2009), and certainly some changes even with task regressed (Fair et al. 2007; Jones et al. 2010). There is also continued debate about what steps should be taken to remove nuisance variable such as heart rate and breathing (Birn et al. 2006; Chang et al. 2009) and whether using a whole brain signal regression to account for these noise effects is appropriate (Fox et al. 2009) or induces spurious negative correlations (Murphy et al. 2009).
