The PDMs of this model show promise in revealing the important dynamic characteristics of the underlying physiological mechanisms and allow the formulation of specific quantitative hypotheses about the role of the sympathetic and parasympathetic activity (corresponding to specific PDMs) in cerebral perfusion and autoregulation. Consistent with the widely held view regarding the temporal characteristics of autonomic control of the cardiovascular system, it is posited that the HR PDMs with a resonant spectral peak around 0.2 Hz may be associated with parasympathetic activity, whereas the PDMs with a resonant spectral peak around 0.12 Hz may be associated with sympathetic activity