Figure 7.
Schematic showing the effect of task on fMRI signals. The present results reveal that the fMRI signal variance, power-law exponent, and Hurst exponent decrease in both task-activated and -deactivated brain regions, suggesting that the dynamic range and long-range memory of the fMRI signal are largest during the baseline resting state. The curves in the top were modeled using Gaussian-distributed white noise filtered in the frequency domain by P ∝ 1/fβ, with β equal to the power-law exponent averaged across the 21 brain regions (rest, 0.83; task, 0.69). The variance during activation/deactivation was modeled as 97.8% of that during rest (average value across 21 brain regions).