title: Withholding and canceling a response in ADHD adolescents.
abstract: BACKGROUND
  Deficient response inhibition in situations involving a trade-off between response execution and response stopping is a hallmark of attention deficit hyperactive disorder (ADHD). There are two key components of response inhibition; reactive inhibition where one attempts to cancel an ongoing response and prospective inhibition is when one withholds a response pending a signal to stop. Prospective inhibition comes into play prior to the presentation of the stop signal and reactive inhibition follows the presentation of a signal to stop a particular action. The aim of this study is to investigate the neural activity evoked by prospective and reactive inhibition in adolescents with and without ADHD.
  
  
  METHODS
  Twelve adolescents with ADHD and 12 age-matched healthy controls (age range 9-18) were imaged while performing the stop signal task (SST).
  
  
  RESULTS
  Reactive inhibition activated right inferior frontal gyrus (IFG) in both groups. ADHD subjects activated IFG bilaterally. In controls, prospective inhibition invoked preactivation of the same part of right IFG that activated during reactive inhibition. In ADHD subjects, prospective inhibition was associated with deactivation in this region. Controls also deactivated the medial prefrontal cortex (MPFC) during prospective inhibition, whereas ADHD subjects activated the same area.
  
  
  CONCLUSIONS
  This pattern of activity changes in the same structures, but in opposite directions, was also evident across all phases of the task in various task-specific areas like the superior and middle temporal gyrus and other frontal areas.
  
  
  CONCLUSIONS
  Differences between ADHD and control participants in task-specific and default mode structures (IFG and MPFC) were evident during prospective, but not during reactive inhibition.
authors.affiliation: Institute of Medical Science, University of Toronto 7213 Medical Sciences Building, 1 King's College Circle, Toronto, Ontario, M5S1A8, Canada ; Neurosciences and Mental Health and the Department of Psychiatry, The Hospital for Sick Children 555 University Avenue, Toronto, Ontario, M5G1X8, Canada.
authors.forename: Mehereen
authors.initials: M
authors.lastname: Bhaijiwala
authors.affiliation: Institute of Medical Science, University of Toronto 7213 Medical Sciences Building, 1 King's College Circle, Toronto, Ontario, M5S1A8, Canada ; Neurosciences and Mental Health and the Department of Psychiatry, The Hospital for Sick Children 555 University Avenue, Toronto, Ontario, M5G1X8, Canada.
authors.forename: Andre
authors.initials: A
authors.lastname: Chevrier
authors.affiliation: Institute of Medical Science, University of Toronto 7213 Medical Sciences Building, 1 King's College Circle, Toronto, Ontario, M5S1A8, Canada ; Neurosciences and Mental Health and the Department of Psychiatry, The Hospital for Sick Children 555 University Avenue, Toronto, Ontario, M5G1X8, Canada.
authors.forename: Russell
authors.initials: R
authors.lastname: Schachar
mesh_terms: D000293:Adolescent; D001289:Attention Deficit Disorder with Hyperactivity / Q000503:physiopathology* / Q000523:psychology; D001931:Brain Mapping; D016022:Case-Control Studies; D002648:Child; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D007266:Inhibition, Psychological; D009483:Neuropsychological Tests; D017397:Prefrontal Cortex / Q000503:physiopathology*
keywords: ADHD; IFG; MPFC; adolescents; fMRI; imaging; proactive inhibition; reactive inhibition; response inhibition; stop-signal task