title: Visual Network Asymmetry and Default Mode Network Function in ADHD: An fMRI Study.
abstract: BACKGROUND
  A growing body of research has identified abnormal visual information processing in attention-deficit hyperactivity disorder (ADHD). In particular, slow processing speed and increased reliance on visuo-perceptual strategies have become evident.
  
  
  OBJECTIVE
  The current study used recently developed fMRI methods to replicate and further examine abnormal rightward biased visual information processing in ADHD and to further characterize the nature of this effect; we tested its association with several large-scale distributed network systems.
  
  
  METHODS
  We examined fMRI BOLD response during letter and location judgment tasks, and directly assessed visual network asymmetry and its association with large-scale networks using both a voxelwise and an averaged signal approach.
  
  
  RESULTS
  Initial within-group analyses revealed a pattern of left-lateralized visual cortical activity in controls but right-lateralized visual cortical activity in ADHD children. Direct analyses of visual network asymmetry confirmed atypical rightward bias in ADHD children compared to controls. This ADHD characteristic was atypically associated with reduced activation across several extra-visual networks, including the default mode network (DMN). We also found atypical associations between DMN activation and ADHD subjects' inattentive symptoms and task performance.
  
  
  CONCLUSIONS
  The current study demonstrated rightward VNA in ADHD during a simple letter discrimination task. This result adds an important novel consideration to the growing literature identifying abnormal visual processing in ADHD. We postulate that this characteristic reflects greater perceptual engagement of task-extraneous content, and that it may be a basic feature of less efficient top-down task-directed control over visual processing. We additionally argue that abnormal DMN function may contribute to this characteristic.
authors: Department of Psychiatry and Biobehavioral Sciences, UCLA Semel Institute for Neuroscience and Human Behavior , Los Angeles, CA , USA.
authors: T Sigi
authors: TS
authors: Hale
authors: Department of Psychiatry and Biobehavioral Sciences, UCLA Semel Institute for Neuroscience and Human Behavior , Los Angeles, CA , USA.
authors: Andrea M
authors: AM
authors: Kane
authors: Department of Psychiatry and Biobehavioral Sciences, UCLA Semel Institute for Neuroscience and Human Behavior , Los Angeles, CA , USA.
authors: Olivia
authors: O
authors: Kaminsky
authors: Department of Psychiatry and Biobehavioral Sciences, UCLA Semel Institute for Neuroscience and Human Behavior , Los Angeles, CA , USA.
authors: Kelly L
authors: KL
authors: Tung
authors: Department of Psychology, University of California Los Angeles , Los Angeles, CA , USA.
authors: Joshua F
authors: JF
authors: Wiley
authors: Department of Psychiatry and Biobehavioral Sciences, UCLA Semel Institute for Neuroscience and Human Behavior , Los Angeles, CA , USA.
authors: James J
authors: JJ
authors: McGough
authors: Department of Psychiatry and Biobehavioral Sciences, UCLA Semel Institute for Neuroscience and Human Behavior , Los Angeles, CA , USA.
authors: Sandra K
authors: SK
authors: Loo
authors: Department of Psychology, Brain and Creativity Institute, University of Southern California , Los Angeles, CA , USA.
authors: Jonas T
authors: JT
authors: Kaplan
keywords: asymmetry; attention; default; laterality; network; sensory; spatial; verbal