T*2 dependence of low frequency functional connectivity

Resting state low frequency (<0.08 Hz) fluctuations in MR timecourses that are temporally correlated between functionally related areas have been observed in recent studies. These fluctuations have been assumed to arise from spontaneous blood oxygenation level-dependent (BOLD) oscillations. This work examines the T-2* characteristics of the low frequency fluctuations (functional connectivity) and compares them to those of task activation induced signal changes. Multi-echo spiral data were fit using a mono-exponential decay model to generate T-2* and intensity (I-0) parameter timecourses. Resultant correlation maps show that both functional connectivity and BOLD activation modulate T-2*, not I-0. Regression analysis also finds that both have a linear dependence on echo time. Thus, functional connectivity and task activation MR signal changes appear to arise from the same BOLD-related origins. (C) 2002 Elsevier Science (USA).