The role of dopamine in dynamic effort-reward integration

Abstract

When deciding to act, the neurotransmitter dopamine is implicated in a valuation of prospective effort and reward. However, its role in dynamic effort-reward integration during action, a process central to everyday behaviour, remains unclear. In a placebocontrolled, within-subject, study, we probed the impact of increasing brain dopamine levels (150 mg of levodopa) and blocking dopamine receptors (1.5 mg of haloperidol) in the context of a novel dynamic effort task in healthy human subjects. We show that modulating homoeostatic dopamine balance distinctly alters implicit and explicit effort allocation as a function of instantaneous reward. Pharmacologically boosting dopamine enhanced motor vigour, reflected in an implicit increase in effort allocation for high rewards. Conversely, pharmacological blockade of dopamine attenuated sensitivity to differences in reward context, reflected in reduced strategic effort discounting. These findings implicate dopamine in an integration of momentary physical experience and instantaneous reward, suggesting a key role of dopamine in acting to maximise reward on the fly.Neuropsychopharmacology (2020) 0:1-6; https://doi.

Effects of Remote Immune Activation on Performance in the 5-Choice Serial Reaction Time Task Following Mild Traumatic Brain Injury in Adolescence

“…Although preference for the sweetened solution is typically thought to reflect anhedonia, the inflammatory effects on motivation appear to relate to reduced effort expenditure, rather than deficits in reward processing (Chudasama et al, 2003 ; Paine et al, 2011 ; Asinof and Paine, 2014 ). Effort expenditure is in part governed by the mPFC which integrates motivational, reward, and cognitive information (van Heesch et al, 2014 ; Yeh et al, 2015 ), with reduced motivation associated with mPFC dysfunction (Felger and Treadway, 2017 ; Michely et al, 2020 ). Such a process could drive the increase in omission rate noted here in the mTBI:LPS animals.…”

“…Indeed, cytokines can potentially affect multiple aspects of dopamine function, leading to decreased synthesis, impaired packaging and release, increased reuptake, or decreased dopamine receptors (Felger and Treadway, 2017 ), providing a potential mechanistic explanation for the ability of LPS treatment to reduce impulsivity. Reduced dopamine is also associated with lower effort-based expenditure (Michely et al, 2020 ) and may thus also account for the decreased motivation seen post-LPS in injured animals. Future work is needed to evaluate the specific effects of acute inflammatory insults on dopaminergic neurotransmission and whether the effects are transient or more long-lasting.…”

Motor response vigour and fixations reflect subjective preferences during intertemporal choice

“…For example, pharmalogical enhancement of dopamine transmission increases the willingness of animals to accept delays and to expend effort to obtain rewards (for a review, see Webber, Lopez-Gamundi, Stamatovich, de Wit, & Wardle, 2020). Two studies with human subjects also reported higher force production in states with augmented dopamine transmission (Chong et al, 2015;Le Bouc et al, 2016;Michely et al, 2020). Further, augmented dopamine transmission increased response vigour (reduced reaction times) in a temporal discounting and reinforcement learning task (Rihet, Possamaï, Micallef-Roll, Blin, & Hasbroucq, 2002;Westbrook et al, 2020;Wagner et al, 2020).…”

“…The integration of reward and effort involves dopaminergic computations (see, e.g. Michely et al, 2020). Congruously, effort-based decision making appears to be disrupted in conditions related to dopaminergic function, such as major depressive disorder and Parkinson's disease (Le Bouc et al, 2016;Yi et al, 2010), underlining the relevance of measuring response vigour during value-based decision making.…”

“…In turn, pharmacological enhancement of dopamine transmission via levodopa in healthy participants increased the force levels exerted to obtain high vs. low rewards. Following debriefing, none of the participants reported to excert higher forces to obtain high rewards (Michely et al, 2020), suggesting that the behaviour reflects an implicit motivational process (Michely et al, 2020). Pessiglione and colleagues (2007) found that participants exert more force to obtain higher rewards even in cases where the rewards have only been presented subliminally.…”