title: The effects of acute tryptophan depletion on costly information sampling: impulsivity or aversive processing?
abstract: BACKGROUND
  The neurotransmitter serotonin (5-HT) has been implicated in both aversive processing and impulsivity. Reconciling these accounts, recent studies have demonstrated that 5-HT is important for punishment-induced behavioural inhibition. These studies focused on situations where actions lead directly to punishments. However, decision-making often involves making tradeoffs between small 'local' costs and larger 'global' losses.
  
  
  OBJECTIVE
  We aimed to distinguish whether 5-HT promotes avoidance of local losses, global losses, or both, in contrast to an overall effect on reflection impulsivity. We further examined the influence of individual differences in sub-clinical depression, anxiety and impulsivity on global and local loss avoidance.
  
  
  METHODS
  Healthy volunteers (N = 21) underwent an acute tryptophan depletion procedure in a double-blind, placebo-controlled crossover design. We measured global and local loss avoidance in a decision-making task where subjects could sample information at a small cost to avoid making incorrect decisions, which resulted in large losses.
  
  
  RESULTS
  Tryptophan depletion removed the suppressive effects of small local costs on information sampling behaviour. Sub-clinical depressive symptoms produced effects on information sampling similar to (but independent from) those of tryptophan depletion. Dispositional anxiety was related to global loss avoidance. However, trait impulsivity was unrelated to information sampling.
  
  
  CONCLUSIONS
  The current findings are consistent with recent theoretical work that characterises 5-HT as pruning a tree of potential decisions, eliminating options expected to lead to aversive outcomes. Our results extend this account by proposing that 5-HT promotes reflexive avoidance of relatively immediate aversive outcomes, potentially at the expense of more globally construed future losses.
authors.affiliation: Behavioural and Clinical Neuroscience Institute, University of Cambridge, Cambridge, England, UK. mollycrockett@gmail.com
authors.forename: M J
authors.initials: MJ
authors.lastname: Crockett
authors.forename: L
authors.initials: L
authors.lastname: Clark
authors.forename: L D
authors.initials: LD
authors.lastname: Smillie
authors.forename: T W
authors.initials: TW
authors.lastname: Robbins
mesh_terms: D000328:Adult; D000596:Amino Acids / Q000097:blood / Q000494:pharmacology; D001007:Anxiety / Q000523:psychology; D003657:Decision Making / Q000187:drug effects / Q000502:physiology; D003863:Depression / Q000523:psychology; D005260:Female; D006801:Humans; D007175:Impulsive Behavior / Q000097:blood / Q000523:psychology*; D008606:Mental Processes / Q000187:drug effects / Q000502:physiology*; D011597:Psychomotor Performance / Q000187:drug effects / Q000502:physiology; D057566:Self Report; D014364:Tryptophan / Q000097:blood / Q000172:deficiency* / Q000502:physiology*
chemical_list: D000596:Amino Acids; D014364:Tryptophan
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