This project involves the application of the SSES methodological approach to the study of basic cognitive and neuropsychological processes and their modulation by the environment. The primary focus of this research is the continuation and expansion of a longstanding collaboration with Dr. Jordan Grafman (Chief Cognitive Neuroscience Section NINDS) centering on the longitudinal Vietnam Head Injury Study (VHIS). Besides this work with Dr. Grafman, there have been two secondary sources of recent SSES publications and findings in this area: 1) the completion of data analyses of SSES experimental studies completed before 1998, 2) collaboration with other researchers in the application of SEM techniques to neuroscience data they have collected. A recent SSES papers based on the analyses of data from SSES cognitive psychological experiments carried out before we stopped conducting such research is Caplan and Schooler (2001. This paper investigates the cognitive processes through which complex environments have their effects. The findings indicate that complex environments encourage rule based learning and transfer; simple environments rote like learning and transfer. Working with Dr. Allen Braun of the National Institute on Deafness and Other Communication Disorders (NIDCD, we applied Structural Equation Modeling to investigate the functional coupling of regional cerebral metabolic rates, as measured by PET, in those with Tourettes Syndrome (TS) and normal individuals (2002). One finding of this delineation of the CSTC circuits and their interrelationships is the existence of functional connections between the motor and lateral orbital frontal circuits in both groups. A reversal in the patterns of these interactions, however, differentiated the patients and the controls; the activity levels in the motor and lateral orbitofrontal circuits were positively correlated in the TS patients and negatively correlated in the normals. These results lend further credence to the hypothesis that altered limbic-motor interactions represent a pathophysiological hallmark of this disease. Most of our collaborative research involves the VHIS. A recent paper (Herrmann, Schooler, Caplan, Lipman, Grafman, Schoenbach, Schwab, K & Johnson, 2001) used SEM to compare alternative theory based models of the structure of memory that differ in the types and numbers of core memory components that they postulate. The analyses utilized data already collected by the VHIS on normal controls and minimally brain injured veterans. This paper reported that for both the normal and minimally brain injured veterans, the SEM model that provided the best fit to the extensive (but not exhaustive) set of VHIS memory measures included four latent factors (verbal episodic, visual episodic, semantic memory and short term memory).