Effects of average reward rate on vigor as a function of individual variation in striatal dopamine

Abstract

RationaleWe constantly need to decide not only which actions to perform, but also how vigorously to perform them. In agreement with an earlier theoretical model, it has been shown that a significant portion of the variance in our action vigor can be explained by the average rate of rewards received for that action. Moreover, this invigorating effect of average reward rate was shown to vary with within-subject changes in dopamine, both in human individuals and experimental rodents. Objectives Here, we assessed whether individual differences in the effect of average reward rate on vigor are related to individual variation in a stable measure of striatal dopamine function in healthy, unmedicated participants. Methods Forty-four participants performed a discrimination task to test the effect of average reward rate on response times to index vigor and completed an [ 18 F]-DOPA PET scan to index striatal dopamine synthesis capacity. ResultsWe did not find an interaction between dopamine synthesis capacity and average reward rate across the entire group. However, a post hoc analysis revealed that participants with higher striatal dopamine synthesis capacity, particularly in the nucleus accumbens, exhibited a stronger invigorating effect of average reward rate among the 30 slowest participants. Conclusions Our findings provide converging evidence for a role of striatal dopamine in average reward rate signaling, thereby extending the current literature on the mechanistic link between average reward rate, vigor, and dopamine.

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

“…They interpreted their finding as facilitated motor responding due to increased dopamine transmission via presynaptic action of low dosages of Haloperidol. Findings of a dopaminergic speeding of RTs in tasks testing response vigor (Guitart-Masip et al, 2011; Hofmans et al, 2021) further support the idea that tyrosine might have reduced RTs via a dopamine-dependent mechanism. However, increased norepinephrine transmission following tyrosine may also have contributed to RT reductions.…”

Evidence for absence of links between striatal dopamine synthesis capacity and working memory capacity, spontaneous eye-blink rate, and trait impulsivity

“…The striatal [ 18 F]-FDOPA uptake values are in the typical range (Supplementary Figure S1), and dopamine synthesis capacity in this dataset has been shown to account for (dopamine drug effects on) effort-based decision making, response vigour, reversal learning, and smartphone social activity in the expected direction (Hofmans et al, 2020(Hofmans et al, , 2022Westbrook et al, 2020Westbrook et al, , 2021. More specifically, [ 18 F]-FDOPA uptake in the striatum was associated positively with the value of cognitive effort (Westbrook et al, 2020), with the impact of average reward value on response vigour (Hofmans et al, 2022) and with dopaminergic drug-related changes in prediction errorrelated BOLD signal in the striatum (van den . The implication of this body of work is that more sophisticated and quantitative indices of value-based learning, motivation, and even daily logs of participants' social activity on their smartphone might be better proxy measures of striatal dopamine synthesis capacity than the simple trait measures reported here.…”

“…Critically, the absence of correlations was not due to measurement error in the estimates of striatal dopamine synthesis capacity or a lack of behavioural relevance of these estimates. The striatal [ 18 F]-FDOPA uptake values are in the typical range (Supplementary Figure S1), and dopamine synthesis capacity in this dataset has been shown to account for (dopamine drug effects on) effort-based decision making, response vigour, reversal learning, and smartphone social activity in the expected direction (Hofmans et al, 2020(Hofmans et al, , 2022Westbrook et al, 2020Westbrook et al, , 2021. More specifically, [ 18 F]-FDOPA uptake in the striatum was associated positively with the value of cognitive effort (Westbrook et al, 2020), with the impact of average reward value on response vigour (Hofmans et al, 2022) and with dopaminergic drug-related changes in prediction errorrelated BOLD signal in the striatum (van den .…”

“…18 F]-FDOPA uptake values are in the typical range (Supplementary Figure 1), and dopamine synthesis capacity in this dataset has been shown to account for (dopamine drug effects on) effort-based decision making, response vigour, reversal learning, and smartphone social activity in the expected direction (Hofmans et al, 2020(Hofmans et al, , 2022Westbrook et al, 2020Westbrook et al, , 2021. More specifically, […”

“…18 F]-FDOPA uptake in the striatum was associated positively with the value of cognitive effort (Westbrook et al, 2020), with the impact of average reward value on response vigour (Hofmans et al, 2022) and with dopaminergic drug-related changes in prediction errorrelated BOLD signal in the striatum (van den . The implication of this body of work is that more sophisticated and quantitative indices of value-based learning, motivation, and even daily logs of participants' social activity on their smartphone might be better proxy measures of striatal dopamine synthesis capacity than the simple trait measures reported here.…”