The main goal of this project is to investigate the neural substrate and cognitive mechanisms that are involved in a set of higher-order "executive" functions that are necessary for goal-directed thinking and behavior. At present there is no unitary model that accounts for all aspects of executive function, but cognitive control is viewed as a common denominator. The frontal lobes and their subdivisions are associated with control functions, but the exact
nature of their associations remains unclear. Stud ies of patients with focal lesions in distinct prefrontal regions are necessary to establish that there is a causal relationship between structure and function. Therefore, we will examine executive control functions in patients with circumscribed injury i n dorsolateral, orbitofrontal/ ventromedial, or medial frontal regions. Lesion etiologies will be cerebrovascular insults, primary cerebral tumors, or traumatic
head injuries. Both conventional anatomical MR images as well as diffusion-weighted MR images will be recorded to identify exact lesion location and degree of diffuse axonal shearing injury. We will define distinct sub-processes of executive control and operationalize them in a series of experiments, using an integrative methodological approach of both behavioral (test results/questionnaires) and functional neuroimaging (fMRI and EEG/ERP) techniques. This will provide electrophysiological, neuroanatomical, blood flow (BOLD responses), and behavioral information on executive control functions. A br oad methodological approach may be necessary to tap the behavioral impairments
observed in some patients with involvement of the frontal lobes, as they are often difficult to measure with traditional neuropsychological tests. Experimental studies can aid in devising new methods for assessing executive deficits, and more detailed functional diagnosis can in turn point to the direction of individual counselling and rehabilitation efforts.