To Do or Not to Do: Dopamine, Affordability and the Economics of Opportunity

Abstract

Five years ago, we introduced the thrift hypothesis of dopamine (DA), suggesting that the primary role of DA in adaptive behavior is regulating behavioral energy expenditure to match the prevailing economic conditions of the environment. Here we elaborate that hypothesis with several new ideas. First, we introduce the concept of affordability, suggesting that costs must necessarily be evaluated with respect to the availability of resources to the organism, which computes a value not only for the potential reward opportunity, but also the value of resources expended. Placing both costs and benefits within the context of the larger economy in which the animal is functioning requires consideration of the different timescales against which to compute resource availability, or average reward rate. Appropriate windows of computation for tracking resources requires corresponding neural substrates that operate on these different timescales. In discussing temporal patterns of DA signaling, we focus on a neglected form of DA plasticity and adaptation, changes in the physical substrate of the DA system itself, such as up- and down-regulation of receptors or release probability. We argue that changes in the DA substrate itself fundamentally alter its computational function, which we propose mediates adaptations to longer temporal horizons and economic conditions. In developing our hypothesis, we focus on DA D2 receptors (D2R), arguing that D2R implements a form of “cost control” in response to the environmental economy, serving as the “brain’s comptroller”. We propose that the balance between the direct and indirect pathway, regulated by relative expression of D1 and D2 DA receptors, implements affordability. Finally, as we review data, we discuss limitations in current approaches that impede fully investigating the proposed hypothesis and highlight alternative, more semi-naturalistic strategies more conducive to neuroeconomic investigations on the role of DA in adaptive behavior.

Comparing Effects of Reward Anticipation on Working Memory in Younger and Older Adults

“…Furthermore, the current result of age-independent reward anticipation benefits (i.e., the benefit from reward context cueing) on working memory accuracy and the quality (or distinctiveness) of information in working memory (as reflected in the parameter of evidence accumulation rate) suggests that reward facilitating effect on selective attention by raising the saliency of content representations in working memory is still preserved in the young-old age range (65 to 78 years of age in the current sample). In contrast, unlike younger adults, the older adults did not become more cautious in their responses in the rewarded context with higher opportunity costs ( Beeler and Mourra, 2018 ; errors are associated with more costs in trials cued with rewards). We think this effect might reflect that reward facilitation of updating context representations in working memory is impaired in old age.…”

“…Second, in light of dopamine’s role in reward processing ( Schultz, 2015 ) and age-related decline in dopamine modulation ( Bäckman et al, 2011 ; Li and Rieckmann, 2014 ), we hypothesized that the effects of reward anticipation would be larger in younger compared to older adults. Specifically, we expected age differences in the effects of reward cueing on facilitating selective encoding and retrieval of the relevant target information through incentivized saliency of reward cued items, thus in improving the rate of evidence accumulation or in increasing response cautiousness (prioritizing accuracy over speed) through more salient context representation of opportunity costs ( Beeler and Mourra, 2018 ; errors in trials associated with anticipated rewards are associated with higher cost). Lastly, in a more exploratory manner we also assessed cognitive processing fluctuation, basic memory storage capacity, and subjective reward sensitivity in order to examine potential behavioral correlates of the reward anticipation effects.…”

Prevalence and predictors of fatigue after aneurysmal subarachnoid hemorrhage

“…Such findings support the notion that inflammatory cytokines lead to dopamine imbalance [14] in the dopaminergic pathways, namely the mesocorticolimbic and nigrostriatal systems. The dopamine imbalance hypothesis states that dopamine may play an important role in the perception of fatigue because it is central for cognition, motivation, and effortful behavior [1,14]. In fact, individuals with high levels of fatigue have reduced mesocorticolimbic connectivity [16].…”

Synchronicity: The Role of Midbrain Dopamine in Generating Whole Brain Coherence, a Hypothesis

“…That is, as 'evidence in favor of prior belief' the representational content of afferent input could be broad. Moreover, a more agnostic view on the representational content driving P(E) opens the door to encoding value on different timescales, such as might arises when different contexts are associated with greater reward availability, or greater opportunity (Beeler and Mourra, 2018;Hamid et al, 2015;Howe et al, 2013).…”

“…In addition, value may be represented on different timescales (Beeler and Mourra, 2018). Moreover, evidence is accumulating that midbrain dopamine may not be restricted solely to value-related signals.…”