title: Site-dependent effects of tDCS uncover dissociations in the communication network underlying the processing of visual search.
abstract: BACKGROUND
  The right posterior parietal cortex (rPPC) and the right frontal eye field (rFEF) form part of a network of brain areas involved in orienting spatial attention. Previous studies using transcranial magnetic stimulation (TMS) have demonstrated that both areas are critically involved in the processing of conjunction visual search tasks, since stimulation of these sites disrupts performance.
  
  
  OBJECTIVE
  This study investigated the effects of long term neuronal modulation to rPPC and rFEF using transcranial direct current stimulation (tDCS) with the aim of uncovering sharing of these resources in the processing of conjunction visual search tasks.
  
  
  METHODS
  Participants completed four blocks of conjunction search trials over the course of 45 min. Following the first block they received 15 min of either cathodal or anodal stimulation to rPPC or rFEF, or sham stimulation.
  
  
  RESULTS
  A significant interaction between block and stimulation condition was found, indicating that tDCS caused different effects according to the site (rPPC or rFEF) and type of stimulation (cathodal, anodal, or sham). Practice resulted in a significant reduction in reaction time across the four blocks in all conditions except when cathodal tDCS was applied to rPPC.
  
  
  CONCLUSIONS
  The effects of cathodal tDCS over rPPC are subtler than those seen with TMS, and no effect of tDCS was evident at rFEF. This suggests that rFEF has a more transient role than rPPC in the processing of conjunction visual search and is robust to longer-term methods of neuro-disruption. Our results may be explained within the framework of functional connectivity between these, and other, areas.
authors.affiliation: Department of Psychology, Durham University, UK. Electronic address: k.l.ball@durham.ac.uk.
authors.forename: Keira
authors.initials: K
authors.lastname: Ball
authors.forename: Alison R
authors.initials: AR
authors.lastname: Lane
authors.forename: Daniel T
authors.initials: DT
authors.lastname: Smith
authors.forename: Amanda
authors.initials: A
authors.lastname: Ellison
mesh_terms: D000328:Adult; D001288:Attention / Q000502:physiology*; D001921:Brain / Q000502:physiology*; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011930:Reaction Time / Q000502:physiology; D014796:Visual Perception / Q000502:physiology*; D055815:Young Adult
keywords: Conjunction search; Frontal eye fields; Posterior parietal cortex; Spatial attention; Transcranial direct current stimulation