Abstract
Operant behavior is not only regulated by factors related to the quality or quantity of reinforcement, but also by the work requirements inherent in performing instrumental actions. Moreover, organisms often make effort-related decisions involving economic choices such as cost/benefit analyses. Effort-based decision making is studied using behavioral procedures that offer choices between high-effort options leading to relatively preferred reinforcers vs. low effort/low reward choices. Several neural systems, including the mesolimbic dopamine (DA) system and other brain circuits, are involved in regulating effort-related aspects of motivation. Considerable evidence indicates that mesolimbic DA transmission exerts a bi-directional control over exertion of effort on instrumental behavior tasks. Interference with DA transmission produces a low-effort bias in animals tested on effort-based choice tasks, while increasing DA transmission with drugs such as DA transport blockers tends to enhance selection of high-effort options. The results from these pharmacology studies are corroborated by the findings from recent articles using optogenetic, chemogenetic and physiological techniques. In addition to providing important information about the neural regulation of motivated behavior, effort-based choice tasks are useful for developing animal models of some of the motivational symptoms that are seen in people with various psychiatric and neurological disorders (e.g., depression, schizophrenia, Parkinson’s disease). Studies of effort-based decision making may ultimately contribute to the development of novel drug treatments for motivational dysfunction.
Highlights
It is often the case that animal models are designed to target neuropsychiatric disorders, it is true that most animal models provide behavioral phenotypes that mimic specific symptoms or dysfunctions rather than entire disorders
Considerable evidence indicates that mesolimbic DA exerts a bi-directional control over exertion of physical effort and effort-based choice
Interference with DA transmission by DA antagonism or depletion produces a low-effort bias in rodents tested on effort-based choice tasks, while increasing DA transmission with drugs such as DA transport blockers tends to enhance selection of high-effort options
Summary
The processes involved in initiating and sustaining instrumental actions, including the exertion of effort needed to overcome obstacles and obtain access to motivationally relevant stimuli, are necessary for survival. A complex environment can involve potential access to several different reinforcers, and distinct paths for accessing them For these reasons, organisms must make choices involving several factors, including cost/benefit assessments based upon work requirements and reinforcement preference (Salamone and Correa, 2002, 2012; Walton et al, 2006; Salamone et al, 2007, 2016a,b,c; Winstanley and Floresco, 2016). If there is no barrier obstructing the arm with the high reinforcement density, rats mostly choose that arm, and neither D1 or D2 family antagonists, nor accumbens DA depletions, nor tetrabenazine alter arm choice (Salamone et al, 1994; Yohn et al, 2015a,b). Interference with DA transmission did not alter preference for the high density of food reward over the low density, did not affect discrimination or reference memory processes related to arm preference, and did not produce an absolute impairment in the ability to climb the barrier
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