New research reveals previously unrecognized behavior disturbances in aging and those with Alzheimer’s disease (AD). Using nonlinear dynamic approaches, Kun Hu, PhD, Steven Shea, PhD and Frank Scheer, PhD, of Brigham and Women’s Hospital, and colleagues found that changes in physical activity during daytime display a robust fractal pattern in healthy young adults and that this pattern is significantly perturbed in elderly people and patients with AD. The perturbed fractal pattern indicates dysfunctions of the activity control network that may involve the master circadian pacemaker or suprachiasmatic nucleus (SCN). These findings are published in the February 6, 2009 Early Edition of the Proceedings of the National Academy of Sciences.

Previous work by the same team has shown that the activity fluctuations of healthy subjects exhibit a fractal structure.  For example, the fluctuations found in small windows of time, such as 10 minutes, are statistically similar to those found in windows of 60 minutes and 6 hours, thus invariant of the time scale. Using animal models,  the researchers also previously showed that the SCN not only controls the circadian cycle but also serves as a major node in the activity control network that generates this fractal activity pattern in rats. Based on the facts that aging and AD are associated with progressive dysfunction of the SCN, the researchers hypothesize that the newly discovered disturbances in activity fractal patterns in elderly subjects and in AD may be linked to the SCN dysfunction in these populations.

Fractal patterns exist in many neurophysiological systems and indicate networks of complex feedback control. Further studies will try to examine how degradation of the SCN-related neuronal interactions contributes to the altered fractal control of activity with aging and those with AD and whether this may have any prognostic value.

This research was supported by grants from the National Institutes of Health and the National Heart, Lung, and Blood Institute.