The low frequency cardiac rhythm (LFCR) is a promising biological marker for psychological research. The primary goal of this project is to make the LFCR methodology more accessible to researchers by providing a both a product and extensive support services. In Phase I, a prototype system was built and used to collect simultaneous physiological and cognitive data from 41 elementary school children. The LFCR consistently decreased when children attended to computerized tasks (i.e., under conditions requiring cognitive persistence). In a preliminary pilot study, children with ADHD did not have the same decrease in the LFCR when they attempted to pay attention on the same tasks; however, they did have decreased LFCR after taking their psycho stimulant medication. A secondary goal of this project is to more firmly establish the biological underpinnings of the LFCR. Prior to the Phase I work, angiotensin activity was hypothesized to mediate the relationship between LFCR, cerebral blood flow and cognitive activity. This hypothesis was partially confirmed with the empirical evidence collected in Phase I. Blood assays validated the connection between LFCR and circulating levels of angiotensin. Transcranial Doppler sonography (TCD) data validated that connection between cerebral blood flow and LFCR. These results provide strong empirical support for the proposed biological model of cognitive persistence. This work will be expanded in Phase II through three main tasks. 1) The prototype will be further refined into a user-friendly commercial product. 2) The database of physiological changes in children and adults during cognitive performance will be enlarged using LFCR, TCD, and blood assays (adults only); ADHD participants will be tested before and after taking medication. 3) Strategic collaborations with researchers will be formed to demonstrate the value of the biological measure in other areas of research. Two impediments currently limit the use of LFCR in research studies. First, the biological basis of LFCR was inadequately characterized. The Phase I and II findings will address this limitation. Second, the methodology is too complex for most researchers without expertise in this area. BioAssessments will overcome this impediment by providing both turnkey equipment and extensive support throughout all stages of the research project. The feasibility of this business model will be demonstrated by Phase II collaborations and publications that serve as case studies. The anticipated Phase III customer will be a researcher studying impulsivity in disorders such as Attention Deficit/Hyperactivity Disorder (ADHD) and substance abuse.