Tryptophan depletion disrupts the motivational guidance of goal-directed behavior as a function of trait impulsivity.
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.
Cools
Roshan
R
Department of Experimental Psychology, University of Cambridge, Cambridge, UK. roshanco@berkeley.edu
Blackwell
Andrew
A
Clark
Luke
L
Menzies
Lara
L
Cox
Sylvia
S
Robbins
Trevor W
TW
D000328:Adult; D000704:Analysis of Variance; D018753:Diet, Protein-Restricted / Q000379:methods; D006040:Goals; D006801:Humans; D007175:Impulsive Behavior / Q000503:physiopathology*; D016014:Linear Models; D008297:Male; D009042:Motivation; D009483:Neuropsychological Tests / Q000706:statistics & numerical data; D010775:Photic Stimulation / Q000379:methods; D011930:Reaction Time / Q000502:physiology*; D012054:Reinforcement, Psychology; D012701:Serotonin / Q000378:metabolism*; D014364:Tryptophan / Q000172:deficiency* / Q000502:physiology
D012701:Serotonin; D014364:Tryptophan