Novel multiscale regulation in human motor activity

Human motor activity is influenced by many factors both extrinsic (work, recreation, reactions to unforeseen random events) and intrinsic (circadian and ultradian rhythms). We investigate if these factors fully account for the complex features observed in recordings of human activity. First, we measure activity over two weeks from forearm motion in subjects undergoing their regular daily routine. We show that no systematic ultradian rhythms exist in human activity during wakefulness. Furthermore, we demonstrate that during wakefulness human activity possesses previously unrecognized dynamic patterns characterized by long-range fractal correlations and nonlinear Fourier phase interactions. These patterns are unaffected by changes in the average activity level occurring within individual subjects throughout the day, on different days, and between subjects. Second, we find that these patterns persist when the same subjects undergo time-isolation laboratory experiments designed to account for the phase of the circadian pacemaker, and to control the known extrinsic factors. We attribute these newly discovered patterns to an intrinsic multi-scale dynamic regulation of human activity that is independent of known extrinsic factors, as well as known intrinsic factors (the circadian and ultradian rhythms).