Top-Down Attentional Control of Visual-Processing

Overview

Background: \- Previous studies have shown that people with certain types of brain damage may have particular problems paying attention and processing things that they see. Researchers are interested in comparing how people with brain damage and without brain damage process visual images. Objectives: \- To better understand the areas of the brain involved in paying attention to things that are seen. Eligibility: \- Individuals at least 18 years of age who either have had damage to one or both sides of specific parts of the brain (e.g., stroke, injury, certain neurosurgery procedures) or are healthy volunteers. Design: * The study involves 4 to 10 visits to the NIH Clinical Center over 1 to 2 years. Each visit will last approximately 2 hours. * Participants will be screened with a medical history and physical examination, and may have the cognitive testing described below during the same visit. * On the first visit and for at least one visit thereafter, participants will have cognitive testing to evaluate thinking and memory. These tests will be either written tests or computer-based tests. * Some participants will qualify for functional magnetic resonance imaging (fMRI) as part of the study. This part will involve a decision-making task that will be performed on a computer during the fMRI scan. Additional scans may be required as directed by the study doctors. * Some randomly selected participants will be asked to have magnetoencephalography (MEG), a procedure to record very small magnetic field changes produced by brain activity. * During the behavioral training, or fMRI or MEG scanning, participants may be monitored with equipment to track eye movements.

Attention is required for most, if not all, perceptual processes. There is a converging body of evidence from single-cell recording studies in monkeys and neuroimaging, behavioral, and clinical studies in humans showing that the processing of attended information is enhanced relative to the processing of unattended information. What is the source of this attentional modulation? Because neuroimaging studies have demonstrated that multiple cortical regions are recruited during tasks involving selective attention, it has proven difficult thus far to determine the differential contributions of each region. A central goal of the proposed research is to characterize the contributions of prefrontal cortex and parietal cortex and test the hypothesis that these regions exert top-down modulatory influences over visual processing areas. Specifically, we wish to investigate the interaction between areas involved in attentional control and visual areas modulated by attention. We propose to study patients with focal lesions and healthy 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 healthy 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.