Chunk #0 — Resting State Functional Connectivity MRI Signal, Brain Networks, and Common Analysis Techniques — Resting State Functional Connectivity MRI (rs-fcMRI) Signal
fMRI studies generally report differences in the brain's BOLD response to various task conditions (i.e., reading words as compared to reading nonwords). However, such task responses are only part of the BOLD signal; large, very slow BOLD signal fluctuations are known to occur in the range of 0.01 to 0.1 Hz. These slow, spontaneous fluctuations occur with or without subjects performing a task. For the types of analysis presented in this review, typically 5–10 min of fMRI data are acquired from subjects resting quietly in the MRI bore (i.e., the resting state). In 1995, Biswal and colleagues first reported that, at rest, low frequency BOLD signal fluctuations appear to define relationships between functionally related regions (Biswal et al. 1995). Specifically, the low-frequency timecourse of a region in somatomotor cortex was found to correlate well with timecourses in the contralateral somatomotor cortex, as well as to timecourses in bilateral ventral thalamus and bilateral supplementary motor areas. These correlations in timecourses are referred to as “functional connectivity”, and an example of these correlations can be found in Fig. 1a.
