The ability to selectively focus attention on portions of our sensory input is a critical brain function that enables us to enhance the processing of high priority stimuli in the environment. For example, a person can listen selectively to one speaker's voice while tuning out several other simultaneous conversations. With vision, attending to a particular part of the visual field results in faster and better discrimination of stimuli in that region of space. The selective averaging capabilities and high temporal resolution of event-related potentials (ERPs) have provided considerable insight into the timing of attention-related brain mechanisms; however, it has proven difficult to precisely specify their anatomical sources. Studies of attention using positron emission tomography (PET) and block-design functional magnetic resonance imaging (fMRI), on the other hand, have identified a number of key brain regions that are part of the circuitry underlying attention, but these studies do not provide information on the timing of the neural activity in the identified brain regions. The present project combines ERPs with fMRI to study both the functional neuroanatomy and timing of visual and auditory attention mechanisms, including attentional filtering of sensory inputs in visual and auditory cortices, the relationship between voluntary attention and putatively automatic sensory-analysis processes, and the neural circuitry of top-down attentional control. Toward these goals, we will incorporate analytic methods that will permit the isolation of brain activity for different aspects of attention and task performance. Five studies -- two visual, two auditory, and one combined auditory and visual -- are proposed, in which normal subjects will perform attention tasks while fMRI scans and high-density ERPs of their brain activity are recorded. These functional imaging data sets will be combined and mapped onto the corresponding structural MM images to investigate the functional circuitry and mechanisms underlying visual and auditory attention in humans. This research has important implications for mental health problems, because disturbances in selective attention contribute to various clinical disorders, including schizophrenia, attention deficit disorder, Alzheimer's disease, hemineglect syndrome, and learning disabilities. The proposed experiments will enhance our understanding of the activation patterns and mechanisms underlying both normal and disordered attention.
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