Use of Transcranial Magnetic Stimulation (TMS) and Magnetic Resonance Imaging (MRI) to Study Visual Attention
Condition: Healthy
Study type: Observational

Summary: 
      The purpose of this study is to learn more about how the brain allows people to focus on
      important objects and filter out unimportant ones when looking at visual images.

      Our senses provide us with a vast amount of information at any given moment in time. For
      example, visual scenes contain many different objects that cannot be processed simultaneously
      because of the limited processing capacity of the brain's visual system. Evidence suggests
      that a a network of brain regions selects relevant information and filters out irrelevant
      information when people view cluttered visual scenes. This study will use transcranial
      magnetic stimulation (TMS) and functional magnetic resonance imaging (fMRI) to determine how
      the different brain regions involved in attentional control and filtering interact.

      Participants in this study will undergo computer tests, an MRI scan, and TMS. During the MRI,
      participants will look at pictures and count objects appearing on a screen. During the TMS,
      participants will perform a computer test. Participants' ability to pay attention will be
      tested with and without TMS. Participants may be asked to return for additional tests in the
      future....
    

Detailed description: 
      Our senses provide us with a vast amount of information at any given moment in time. For
      example, visual scenes contain many different objects that cannot all be processed
      simultaneously because of the limited processing capacity of the visual system. Therefore,
      attentional mechanisms are required to select relevant objects and filter out irrelevant
      ones. There is converging evidence from single-cell recording and lesion studies in monkeys
      and functional brain imaging studies in humans that irrelevant information from cluttered
      visual scenes is filtered out in extrastriate visual cortex. Functional brain imaging studies
      also suggest that these attentional filtering mechanisms are mediated by top-down feedback
      signals arising in higher-order areas in frontal and parietal cortex. However, it is not
      clear from these studies whether these frontal and parietal brain regions are functionally
      significant in attentional control of behavior.

      Transcranial magnetic stimulation (TMS) applied over a particular cortical region can
      interfere with cognitive processing in that region, thereby creating a virtual disruption in
      the intact human cerebral cortex. Hence, this tool can be used to determine if a brain region
      is functionally involved in the performance of a given cognitive function. In the proposed
      study, we wish to use TMS to test the hypothesis that attentional filter mechanisms operating
      in extrastriate cortex are under "top-down" control by regions in the frontal and parietal
      cortex. Our approach will use a combination of TMS and functional magnetic resonance imaging
      (fMRI).

      First, subjects will participate in an fMRI experiment (93-M-0170) designed to localize the
      cortical regions of interest (ROIs) that are involved with attentional processing for each
      subject. Second, TMS will be used to create transient virtual disruptions in frontal and
      parietal ROIs of normal volunteers while they perform a task requiring spatial attention. We
      hypothesize that, when TMS is used to interfere with attentional processing, subjects will
      show impaired performance in a task that requires them to filter out irrelevant visual
      information. In contrast, performance during TMS should not suffer in a control task in which
      no irrelevant information needs to be filtered out.
    

Keywords: Transcranial Magnetic Stimulation; Parietal Lobe; fMRI; Cognition; Perception; Cortical Stimulation; Spatial Attention