This is a competing continuation applicaiton for investigating the neurobiological foundations of spatial orientation (directed sensory attention) in the healthy and injured human brain. The investigations proposed in this application will revolve around a unified approach to account for the behavioral and anatomical heterogeneity of hemispatial neglect. Acoording to this approach, the anatomical substrate of spatial attention takes the form of a distributed, large-scale network with three monosynaptically interconnected cortical components (frontal, parietal, and cingulate) each of which makes a different contribution to spatial orientation. Damage to components of this network yield the various manifestations of hemispatial neglect. Our goal is to characterize the detail organization of this network its hemispheric dominance patterns, and its relationship to hemispatial neglect. To this end, we propose to continue the computerized phschophysical testing of an unselected sample of patients with focal strokes and to initiate new functional MRI studies in young, healthy volunteers. We have chosen this two-pronged approach because of the complementary nature of studying cognitive deficits by functional imaging and focal lesion analysis. Hemispatial neglect is a common and devastating consequence of brain injury. Understanding the organization of the associated neural network will be important in designing methods of treatment and rehabilitation. In addition, since the large-scale network approach which has shaped the hypotheses for this project is relevant to the organization of other cognitive domains, a clearer understanding of the neural substrate of spatial orientation is likely to provide considerable insights into the cerebral representation of other cognitive functions.