 We propose to study patients with focal lesions and normal volunteers while they perform tasks requiring attention. Subjects will participate, first, in a series of behavioral studies involving selective attention; the relative performance of different patient groups and neurologically normal volunteers will be compared. Subjects will also be studied while performing similar tasks during functional magnetic resonance imaging fMRI. We hypothesize that selective attention will be heavily impaired by lesions of key prefrontal e.g., dorsolateral prefrontal cortex and key parietal e.g., superior parietal lobule sites. We also expect that brain imaging data will show decreased activation in visual regions ipsilateral to the focal lesions in prefrontal and parietal cortex, thus providing evidence that prefrontal and parietal cortex are sources of top-down modulation. Although other research groups have compared the behavior of patients with various focal lesions or have performed fMRI studies of visual attention in neurologically normal patients, we are unaware of any concerted effort to perform fMRI in patients with focal lesions in order to functionally isolate the contributions of individual cortical regions that serve as critical nodes in the attentional network. 