Dopamine, Behavioral Economics, and Effort

Abstract

There are numerous problems with the hypothesis that brain dopamine (DA) systems, particularly in the nucleus accumbens, directly mediate the rewarding or primary motivational characteristics of natural stimuli such as food. Research and theory related to the functions of mesolimbic DA are undergoing a substantial conceptual restructuring, with the traditional emphasis on hedonia and primary reward yielding to other concepts and lines of inquiry. The present review is focused upon the involvement of nucleus accumbens DA in behavioral activation and effort-related processes. Viewed from the framework of behavioral economics, the effects of accumbens DA depletions and antagonism on food-reinforced behavior are highly dependent upon the work requirements of the instrumental task, and DA depleted rats are more sensitive to increases in response costs (i.e., ratio requirements). Moreover, interference with accumbens DA transmission exerts a powerful influence over effort-related choice behavior. Rats with accumbens DA depletions or antagonism reallocate their instrumental behavior away from food-reinforced tasks that have high response requirements, and instead these rats select a less-effortful type of food-seeking behavior. Nucleus accumbens DA and adenosine interact in the regulation of effort-related functions, and other brain structures (anterior cingulate cortex, amygdala, ventral pallidum) also are involved. Studies of the brain systems regulating effort-based processes may have implications for understanding drug abuse, as well as energy-related disorders such as psychomotor slowing, fatigue or anergia in depression and other neurological disorders.

Neurogenetics and Pharmacology of Learning, Motivation, and Cognition

“…It is to be noted that the same Go-NoGo mechanisms, operating in the ventral striatum as opposed to dorsal striatum coding of specific instrumental actions, can support the selection of general Pavlovian approach 'actions' in pursuit of rewards. These motor and motivational effects are supported by empirical observations, such that increased response-reward probabilities, DA release, or pharmacological DA stimulation, are associated with speeded responding and motivated behavior (eg, Satoh et al, 2003;Nakamura and Hikosaka, 2006;Everitt and Robbins, 2005;Robbins and Everitt, 2007;Salamone et al, 2009;Farrar et al, 2010). Similarly, the cost of performing an effortful action can be modulated through manipulation of the ventral-striatopallidal NoGo pathway (Mingote et al, 2008).…”

“…This conceptualization fits with the observation that striatal activation predicts the extent to which working memory updating can be trained (Dahlin et al, 2008a). Further, in addition to learning effects, dopaminergic agents can also directly potentiate effortful motivated behavior (Salamone et al, 2009;Farrar et al, 2010).…”

The role of learning-related dopamine signals in addiction vulnerability

“…One likely and important issue is that Saunders and Robinson (2012) manipulated not only phasic but also tonic dopamine signals. Indeed, the most prominent effects of manipulations of dopamine are not alterations in learning, but profound changes in the rate and vigour at which behaviour is emitted (Salamone et al, 2009). The reinforcement learning framework reviewed above does not account for this, but semi-Markov, average reinforcement learning formulations do (Niv et al, 2007).…”

Conflict acts as an implicit cost in reinforcement learning

“…In fact, striatal dopamine has been particularly implicated in the cost of effort. A greater willingness to expend effort is related to increased striatal dopaminergic tone 11,12 and can be induced with dopamine agonism 13,14 . Conversely, dopamine depletion or antagonism diminishes the willingness to trade effort for reward [14][15][16] .…”

“…A greater willingness to expend effort is related to increased striatal dopaminergic tone 11,12 and can be induced with dopamine agonism 13,14 . Conversely, dopamine depletion or antagonism diminishes the willingness to trade effort for reward [14][15][16] . Structurally, D2 receptor overexpression shifts the cost/benefit calculation towards greater cost 17,18 .…”