title: BOLD correlates of trial-by-trial reaction time variability in gray and white matter: a multi-study fMRI analysis.
abstract: BACKGROUND
  Reaction time (RT) is one of the most widely used measures of performance in experimental psychology, yet relatively few fMRI studies have included trial-by-trial differences in RT as a predictor variable in their analyses. Using a multi-study approach, we investigated whether there are brain regions that show a general relationship between trial-by-trial RT variability and activation across a range of cognitive tasks.
  
  
  RESULTS
  The relation between trial-by-trial differences in RT and brain activation was modeled in five different fMRI datasets spanning a range of experimental tasks and stimulus modalities. Three main findings were identified. First, in a widely distributed set of gray and white matter regions, activation was delayed on trials with long RTs relative to short RTs, suggesting delayed initiation of underlying physiological processes. Second, in lateral and medial frontal regions, activation showed a "time-on-task" effect, increasing linearly as a function of RT. Finally, RT variability reliably modulated the BOLD signal not only in gray matter but also in diffuse regions of white matter.
  
  
  CONCLUSIONS
  The results highlight the importance of modeling trial-by-trial RT in fMRI analyses and raise the possibility that RT variability may provide a powerful probe for investigating the previously elusive white matter BOLD signal.
authors.affiliation: Department of Psychology, Washington University, Saint Louis, Missouri, United States of America. tyarkoni@wustl.edu
authors.forename: Tal
authors.initials: T
authors.lastname: Yarkoni
authors.forename: Deanna M
authors.initials: DM
authors.lastname: Barch
authors.forename: Jeremy R
authors.initials: JR
authors.lastname: Gray
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Conturo
authors.forename: Todd S
authors.initials: TS
authors.lastname: Braver
mesh_terms: D000328:Adult; D001288:Attention / Q000502:physiology; D001921:Brain / Q000378:metabolism* / Q000473:pathology* / Q000502:physiology; D001931:Brain Mapping / Q000379:methods*; D003657:Decision Making; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D011597:Psychomotor Performance / Q000502:physiology; D011930:Reaction Time / Q000502:physiology; D015203:Reproducibility of Results; D012559:Schizophrenia / Q000473:pathology; D013997:Time Factors