Tryptophan depletion disinhibits punishment but not reward prediction: implications for resilience

Item does not contain fulltextRATIONALE: We have previously shown that tryptophan depletion enhances punishment but not reward prediction (Cools et al. in Neuropsychopharmacology 33:2291-2299, 2008b). This provided evidence for a valence-specific role of serotonin (which declines under depleted tryptophan) in aversive processing. Recent theoretical (Dayan and Huys in PLoS Comput Biol 4:e4, 2008) and experimental (Crockett et al. in J Neurosci 29:11993-11999, 2009) approaches have, however, further specified this role by showing that serotonin is critical for punishment-induced inhibition. OBJECTIVES: We sought to examine the role of serotonin in punishment-induced inhibition. We also examined the impact of induced mood on this effect to assess whether effects of tryptophan depletion on affective inhibition are moderated by mood. METHODS: Healthy females consumed a balanced amino acid mixture with (N = 20) or without (N = 21) the serotonin precursor tryptophan. Each subject completed either negative or neutral mood induction. All subjects completed the reward and punishment reversal learning task adopted in the previous study. RESULTS: We demonstrate a punishment prediction impairment in individuals who consumed tryptophan which was absent in individuals who were depleted of tryptophan. This effect was impervious to mood state. CONCLUSIONS: Our results suggest that serotonin promotes the inhibition of responses to punishing outcomes. This may lead to reduced punishment prediction accuracy in the presence of tryptophan and may contribute to resilience to affective disorders. Reduction of serotonin via tryptophan depletion then removes this inhibition. As such, we highlight a mechanism by which reduced serotonin can contribute to disorders of impulsivity and compulsivity as well as disorders of emotion.1 januari 201

The Rationale for Consuming Cognitive Enhancement Drugs in University Students and Teachers

Sattler S, Sauer C, Mehlkop G, Graeff P. The Rationale for Consuming Cognitive Enhancement Drugs in University Students and Teachers. PLoS ONE. 2013;8(7): e68821.Cognitive enhancement (CE) is the pharmaceutical augmentation of mental abilities (e.g., learning or memory) without medical necessity. This topic has recently attracted widespread attention in scientific and social circles. However, knowledge regarding the mechanisms that underlie the decision to use CE medication is limited. To analyze these decisions, we used data from two online surveys of randomly sampled university teachers (N = 1,406) and students (N = 3,486). Each respondent evaluated one randomly selected vignette with regard to a hypothetical CE drug. We experimentally varied the characteristics of the drugs among vignettes and distributed them among respondents. In addition, the respondent’s internalization of social norms with respect to CE drug use was measured. Our results revealed that students were more willing to enhance cognitive performance via drugs than university teachers, although the overall willingness was low. The probability of side effects and their strength reduced the willingness to use CE drugs among students and university teachers, whereas higher likelihoods and magnitudes of CE increased this propensity. In addition, the internalized norm against CE drug use influenced decision making: Higher internalization decreased the willingness to use such medications. Students’ internalized norms more strongly affected CE abstinence compared with those of university teachers. Furthermore, internalized norms negatively interacted with the instrumental incentives for taking CE medication. This internalization limited the influence of and deliberation on instrumental incentives. This study is the first to provide empirical evidence regarding the importance of social norms and their influence on rational decision making with regard to CE. We identified previously undiscovered decision-making patterns concerning CE. Thus, this study provides insight into the motivators and inhibitors of CE drug use. These findings have implications for contending with CE behavior by highlighting the magnitude of potential side effects and by informing the debate regarding the ethics of CE use