title: Methylphenidate but not atomoxetine or citalopram modulates inhibitory control and response time variability.
abstract: BACKGROUND
  Response inhibition is a prototypical executive function of considerable clinical relevance to psychiatry. Nevertheless, our understanding of its pharmacological modulation remains incomplete.
  
  
  METHODS
  We used a randomized, double-blind, placebo-controlled, crossover design to examine the effect of an acute dose of methylphenidate (MPH) (30 mg), atomoxetine (ATM) (60 mg), citalopram (CIT) (30 mg), and placebo (PLAC) (dextrose) on the stop signal inhibition task in 24 healthy, right-handed men 18-35 years of age. Participants performed the task under each of the four drug conditions across four consecutive sessions.
  
  
  RESULTS
  Methylphenidate led to a reduction in both response time variability and stop-signal reaction time (SSRT), indicating enhanced response inhibition compared with all other drug conditions. Crucially, the enhancement of response inhibition by MPH occurred without concomitant changes in overall response speed, arguing against a simple enhancement of processing speed. We found no significant differences between ATM and PLAC, CIT and PLAC, or ATM and CIT for either response time variability or SSRT.
  
  
  CONCLUSIONS
  An acute dose of MPH but not ATM or CIT was able to improve SSRT and reduce response time variability in nonclinical participants. Improvements in response inhibition and response variability might underlie the reported clinical benefits of MPH in disorders such as attention-deficit/hyperactivity disorder.
authors.affiliation: University of Queensland, Queensland Brain Institute and School of Psychology, Brisbane, Australia.
authors.forename: L Sanjay
authors.initials: LS
authors.lastname: Nandam
authors.forename: Robert
authors.initials: R
authors.lastname: Hester
authors.forename: Joe
authors.initials: J
authors.lastname: Wagner
authors.forename: Tarrant D R
authors.initials: TD
authors.lastname: Cummins
authors.forename: Kelly
authors.initials: K
authors.lastname: Garner
authors.forename: Angela J
authors.initials: AJ
authors.lastname: Dean
authors.forename: Bung Nyun
authors.initials: BN
authors.lastname: Kim
authors.forename: Pradeep J
authors.initials: PJ
authors.lastname: Nathan
authors.forename: Jason B
authors.initials: JB
authors.lastname: Mattingley
authors.forename: Mark A
authors.initials: MA
authors.lastname: Bellgrove
mesh_terms: D000293:Adolescent; D018759:Adrenergic Uptake Inhibitors / Q000494:pharmacology*; D000069445:Atomoxetine Hydrochloride; D015283:Citalopram / Q000494:pharmacology*; D018592:Cross-Over Studies; D018765:Dopamine Uptake Inhibitors / Q000494:pharmacology*; D004311:Double-Blind Method; D006801:Humans; D007266:Inhibition, Psychological; D008297:Male; D008774:Methylphenidate / Q000494:pharmacology*; D009483:Neuropsychological Tests; D011437:Propylamines / Q000494:pharmacology*; D011930:Reaction Time / Q000187:drug effects*; D017367:Selective Serotonin Reuptake Inhibitors / Q000494:pharmacology*
chemical_list: D018759:Adrenergic Uptake Inhibitors; D000069445:Atomoxetine Hydrochloride; D015283:Citalopram; D018765:Dopamine Uptake Inhibitors; D008774:Methylphenidate; D011437:Propylamines; D017367:Selective Serotonin Reuptake Inhibitors