Systems, methods, and other techniques for monitoring, including non-invasive monitoring, of biological markers based on the interaction, temporal association, or coincidence of brain activity and periphery activity in a mammal are provided. Systems and methods for generating a behavioral state-independent representation of cardiac activity and for identifying cardiac events and/or brain-periphery, e.g., brain-cardiac, temporal associations useful as biomarkers of disease such as, e.g., neurologic disease, in a mammal are also provided.