Attention and Visual Perception
Condition: Focal Lesions; Focal Brain Lesion
Study type: Observational

Summary: 
      The NIMH is conducting studies aimed at gaining a better understanding of the areas of the
      brain that are involved in different types of mental processes. This study will focus on
      brain regions involved in visual perception and attention.

      Healthy normal volunteers and people who have had a stroke or undergone neurosurgery may be
      eligible for this study. Candidates must be 18 years of age or older, They must not have a
      history of a psychiatric disorder, including depression, anxiety, psychosis, or neurological
      disease other than stroke or the previous neurosurgery.

      Participants undergo the following tests and procedures during four or more visits to the NIH
      Clinical Center:

        -  Physical and neurological examinations and depression rating scale.

        -  Cognitive testing: Subjects complete written tests, sit at a computer and make decisions
           about what they are shown by pressing keys, or answer questions from a test examiner.

        -  Behavioral training: Subjects practice performing a cognitive task that involves looking
           at and making decisions about visual images that appear on a computer screen.

        -  Magnetic resonance imaging (MRI): Subjects undergo MRI scanning while they perform the
           task they previously practiced. The MRI scanner is a metal cylinder surrounded by a
           strong magnetic field. During the procedure, subjects lie still for up to 10 minutes at
           a time on a table that can slide in and out of the cylinder. The entire MRI scanning
           session takes about one hour. There are multiple scans which each can take up to 10
           minutes. They may be asked to return for one or two additional scanning sessions.

      During the behavioral training or MRI scanning, special pieces of equipment that monitor eye
      movements may be used.

      Some subjects may be asked to return to NIH for an additional visit to participate in a
      magnetoencephalographic scan. This test uses several sensors applied to the scalp to measure
      very small changes in magnetic fields. This is another way to measure brain activity.
    

Detailed description: 
      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 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.
    

Keywords: Attention; Executive Function; Vision; fMRI; Top-Down; Visual Processing; Lesion; Prefrontal; Parietal; Focal Brain Lesion; Healthy Volunteer