Tryptophan depletion disrupts the motivational guidance of goal-directed behavior as a function of trait impulsivity

Neuropsychopharmacology. 2005 Jul;30(7):1362-73. doi: 10.1038/sj.npp.1300704.


Serotonin (5-HT) is well known to affect the motivational properties of stimuli predictive of rewards as well as the inhibitory control of behavior. Here, central 5-HT depletion was induced by the acute tryptophan (TRP) depletion (ATD) procedure in young healthy volunteers to examine the role of 5-HT in motivated action and prepotent response inhibition. A novel reaction-time task, tailored to individual differences in general cognitive speed, was employed to measure the guidance of behavior by motivationally relevant signals predictive of reinforcement likelihood, while the stop-signal reaction-time task was used to measure response inhibition. Following the TRP-balancing control drink, cues predictive of high-reinforcement certainty induced faster, but less accurate responses compared with cues predictive of lower reinforcement certainty. Depletion of central 5-HT modulated this coupling between motivation and action by slowing responses and increasing accuracy as a function of incentive certainty. These effects of ATD on motivated action correlated highly with individual differences in the personality trait of Nonplanning Impulsiveness (Barratt Impulsivity Scale (BIS-11)), so that strongest effects on motivated action were observed in high-impulsive individuals. By contrast, ATD left unaltered the ability to inhibit prepotent responses. Our findings may have implications for a variety of neuropsychiatric disorders including impulsive aggressive disorders and depression.

Publication types

  • Clinical Trial
  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Analysis of Variance
  • Diet, Protein-Restricted / methods
  • Goals*
  • Humans
  • Impulsive Behavior / physiopathology*
  • Linear Models
  • Male
  • Motivation*
  • Neuropsychological Tests / statistics & numerical data
  • Photic Stimulation / methods
  • Reaction Time / physiology*
  • Reinforcement, Psychology
  • Serotonin / metabolism*
  • Tryptophan / deficiency*
  • Tryptophan / physiology


  • Serotonin
  • Tryptophan