title: Acute serotonin depletion releases motivated inhibition of response vigour.
abstract: BACKGROUND
  The neurotransmitter serotonin has long been implicated in the motivational control of behaviour. Recent theories propose that the role of serotonin can be understood in terms of an interaction between a motivational and a behavioural activation axis. Experimental support for these ideas, however, has been mixed.
  
  
  OBJECTIVE
  In the current study, we aimed to investigate the role of serotonin (5HT) in behavioural vigour as a function of incentive motivation.
  
  
  METHODS
  We employed dietary acute tryptophan depletion (ATD) to lower the 5HT precursor tryptophan during the performance of a speeded visual discrimination task. Feedback valence and feedback probability were manipulated independently and cued prior to target onset. On feedback trials, fast correct responses led to either reward or avoidance of punishment, while slow or incorrect responses led to reward omission or punishment.
  
  
  RESULTS
  We show that behavioural responding is inhibited under high incentive motivation (i.e. high-feedback probability) at baseline 5HT levels and that lowering these leads to behavioural disinhibition, while leaving accuracy unaffected. Surprisingly, there were no differential effects of motivational valence, with 5HT depletion releasing behavioural inhibition under both appetitive and aversive motivation.
  
  
  CONCLUSIONS
  Our findings extend current theories on the role of 5HT in behavioural inhibition by showing that reductions in serotonin lead to increased behavioural vigour only if there is a motivational drive to inhibit behaviour at baseline.
authors.affiliation: Donders Institute for Brain, Cognition and Behaviour, Radboud University, Nijmegen, Netherlands, h.denouden@donders.ru.nl.
authors.forename: Hanneke E M
authors.initials: HE
authors.lastname: den Ouden
authors.forename: Jennifer C
authors.initials: JC
authors.lastname: Swart
authors.forename: Kristin
authors.initials: K
authors.lastname: Schmidt
authors.forename: Durk
authors.initials: D
authors.lastname: Fekkes
authors.forename: Dirk E M
authors.initials: DE
authors.lastname: Geurts
authors.forename: Roshan
authors.initials: R
authors.lastname: Cools
mesh_terms: D000293:Adolescent; D000328:Adult; D018592:Cross-Over Studies; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D007266:Inhibition, Psychological; D008297:Male; D009042:Motivation / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods; D011930:Reaction Time / Q000502:physiology*; D012701:Serotonin / Q000172:deficiency*; D014364:Tryptophan / Q000172:deficiency*; D055815:Young Adult
chemical_list: D012701:Serotonin; D014364:Tryptophan