A single dose of the catecholamine precursor Tyrosine reduces physiological arousal and decreases decision thresholds in reinforcement learning and temporal discounting

Abstract

Supplementation with the catecholamine precursor L-Tyrosine might enhance cognitive performance, but overall findings are mixed. Here, we investigate the effect of a single dose of tyrosine (2g) vs. placebo on two key aspects of catecholamine-dependent decision-making: model-based reinforcement learning (2-step task) and temporal discounting, using a double-blind, placebo-controlled, within-subject design (n=28 healthy male participants). We leveraged drift diffusion models in a hierarchical Bayesian framework to jointly model participants' choices and response times in both tasks. Furthermore, comprehensive autonomic monitoring (heart rate, heart rate variability, pupillometry, spontaneous eye-blink rate) was performed both pre- and post-supplementation, to explore potential physiological effects of supplementation. Across tasks, tyrosine consistently reduced participants' RTs without deteriorating task-performance. Diffusion modeling linked this effect to attenuated decision-thresholds in both tasks and further revealed increased model-based control (2-step task) and (if anything) attenuated temporal discounting. On the physiological level, participants pupil dilation was predictive of the individual degree of temporal discounting. Tyrosine supplementation reduced physiological arousal as revealed by increases in pupil dilation variability and reductions in hear rate. Supplementation-related changes in physiological arousal predicted individual changes in temporal discounting. Our findings provide first evidence that tyrosine supplementation might impact psychophysiological parameters, and suggest that modeling approaches based on sequential sampling models can yield novel insights into latent cognitive processes modulated by amino-acid supplementation.

Erotic cue exposure increases physiological arousal, biases choices towards immediate rewards and attenuates model-based reinforcement learning

“…via L-Dopa or Haloperidol) intake modulates both model-based control (Wunderlich et al, 2010; Sharp et al, 2016) and temporal discounting (de Wit et al, 2002; Pine et al, 2010; Wagner et al, 2020). Recently, we found that a single dose of the catecholamine precursor L-Tyrosine resulted in faster response times in both tasks due to reduced decision thresholds according to DDM (Mathar et al, 2022). However, the findings regarding dopaminergic manipulation of both model-based control (Kroemer et al, 2019; Deserno et al, 2021) and delay discounting (Petzold et al, 2019) are still heterogeneous.…”

“…Based on suggestions by Kool et al (2016) we modified the outcome stage by replacing the fluctuating reward probabilities (reward / no reward) with fluctuating reward magnitudes (Gaussian random walks with reflecting boundaries at 0 and 100, and standard deviation of 2.5). This task version has been successfully applied in a number of recent papers from our group (Mathar et al, 2022; Wagner et al, 2022).…”

“…However, this finding was challenged recently (Deserno et al, 2021;Kroemer et al, 2019). In recent own work, we found that a single dose of the catecholamine precursor L-Tyrosine enhances model-based reinforcement learning to some extend in healthy participants (Mathar et al, 2022). However, whether model-based control is also partly under contextual control in a similar manner to temporal discounting, is still elusive.…”

Dopamine regulates decision thresholds in human reinforcement learning

“…As noted by the authors, this might also be due to dose-dependent presynaptic effects of Bromocriptine, which might have resulted in a net reduction in DA transmission 53 . But another possibility is that DA might specifically contribute to threshold adjustments in value-based decision settings 51 . This idea resonates with the role of dopamine in regulating response vigor [34][35][36][37] .…”

“…Likewise, increased DA availability in mice increases response rates in the absence of learning 50 , again consistent with a threshold reduction. In humans, administration of the catecholamine precursor tyrosine reduces decision thresholds across different value-based decision-making tasks 51 , and the DA agonist ropinirole reduces decision thresholds during inhibition 52 . In contrast, Bromocriptine (a DA agonist) does not affect thresholds during perceptual decision-making 53 , suggesting that such effects might be task dependent.…”