Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
Comparative Study
. 2015 Mar;40(4):1005-15.
doi: 10.1038/npp.2014.285. Epub 2014 Oct 20.

Dopamine Antagonism Decreases Willingness to Expend Physical, but Not Cognitive, Effort: A Comparison of Two Rodent Cost/Benefit Decision-Making Tasks

Affiliations
Free PMC article
Comparative Study

Dopamine Antagonism Decreases Willingness to Expend Physical, but Not Cognitive, Effort: A Comparison of Two Rodent Cost/Benefit Decision-Making Tasks

Jay G Hosking et al. Neuropsychopharmacology. .
Free PMC article

Abstract

Successful decision making often requires weighing a given option's costs against its associated benefits, an ability that appears perturbed in virtually every severe mental illness. Animal models of such cost/benefit decision making overwhelmingly implicate mesolimbic dopamine in our willingness to exert effort for a larger reward. Until recently, however, animal models have invariably manipulated the degree of physical effort, whereas human studies of effort have primarily relied on cognitive costs. Dopamine's relationship to cognitive effort has not been directly examined, nor has the relationship between individuals' willingness to expend mental versus physical effort. It is therefore unclear whether willingness to work hard in one domain corresponds to willingness in the other. Here we utilize a rat cognitive effort task (rCET), wherein animals can choose to allocate greater visuospatial attention for a greater reward, and a previously established physical effort-discounting task (EDT) to examine dopaminergic and noradrenergic contributions to effort. The dopamine antagonists eticlopride and SCH23390 each decreased willingness to exert physical effort on the EDT; these drugs had no effect on willingness to exert mental effort for the rCET. Preference for the high effort option correlated across the two tasks, although this effect was transient. These results suggest that dopamine is only minimally involved in cost/benefit decision making with cognitive effort costs. The constructs of mental and physical effort may therefore comprise overlapping, but distinct, circuitry, and therapeutic interventions that prove efficacious in one effort domain may not be beneficial in another.

Figures

Figure 1
Figure 1
Experimental timeline and task schematics. (a) Timeline for the experiment. After establishing baseline behavior on the rat cognitive effort task (rCET), half of the cohort remained on the rCET and half were switched to the physical effort-discounting task (EDT). (b) Trial structure for the rCET. Trials began when the food tray light was illuminated. A nosepoke response in the food tray extinguished the light and extended the levers. Each lever was permanently designated to initiate either low-effort/low-reward (LR) or high-effort/high-reward (HR) trials. When animals pressed one of the levers, both levers retracted and a 5-s intertrial interval (ITI) began. Following the ITI, one of the five stimulus lights briefly illuminated, 1.0 s for a LR trial and 0.2 s for a HR trial. If animals nosepoked in the previously illuminated aperture within 5 s (a correct response), they were rewarded 1 sugar pellet for a LR trial and 2 sugar pellets for a HR trial. The food tray light then illuminated to signal the opportunity to start the next trial. A number of behaviors led to a 5-s time-out, signaled by house light illumination: failure to make a lever response (choice omission); failure to withhold responding during the ITI (premature response); nosepoke in an unlit hole following the stimulus (incorrect response); and failure to make a nosepoke response following the stimulus (response omission). Figure is reprinted with permission from Cocker et al (2012). (c) Trial structure for the EDT. New trials were presented every 40 s with illumination of the tray light, followed by the extension of the levers. If animals responded on the LR lever, both levers retracted and the animal immediately received 2 sugar pellets; this cost (ie, a single lever press, FR1) remained constant for LR trials across the session. If animals responded on the HR lever, the LR lever retracted and animals were given 25 s to complete a higher number of presses for 4 sugar pellets. The HR costs increased across the session, beginning with FR2 in the first block, followed by FR5, FR10, and FR20. Animals did not receive reward if they failed to make a lever response (choice omission) or if they failed to complete the required number of lever presses for a HR trial (incomplete HR response), although these occurred less than once per session per animal from the outset. Modified with permission from Floresco et al (2008).
Figure 2
Figure 2
Dopamine and norepinephrine pharmacology on the rCET. (a–f) Neither the dopamine D2-family receptor antagonist eticlopride nor the D2-family receptor antagonist SCH23390 affected animals' choice, accuracy, or premature responding. (g–i) Although the α2-adrenergic receptor antagonist yohimbine did not affect animals' choice (g) or premature responding (i), it significantly decreased accuracy at the highest dose for all trial types. (j–l) The selective norepinephrine reuptake inhibitor atomoxetine had no effect on animals' choice (j) and premature responding (l) and virtually no effect on accuracy, with only a trend to decrease workers' performance on LR trials. Data are shown as the mean percent for each variable (±SEM).
Figure 3
Figure 3
Baseline behavior on the EDT versus rCET. (a) During the first three sessions, all animals demonstrated sensitivity to the physical effort costs: choice of HR decreased across blocks as the costs increased. Remarkably, and despite reversing the lever/reward contingencies from the rCET to the EDT, the worker/slacker distinction held during these early sessions of the EDT: animals that had been deemed ‘workers' for the rCET remained workers for the EDT, and it was similar for slackers. (b) Baseline choice behavior on the rCET was linearly correlated with choice behavior on sessions 1–3 of the EDT. (c) However, upon reaching stability at sessions 13–15, the worker/slacker distinction was no longer valid for the EDT, although animals were still sensitive to the increasing physical effort costs, overall. (d) No correlation to baseline behavior on the rCET was observed for sessions 13–15. Data (a, c) are shown as the mean percent (±SEM).
Figure 4
Figure 4
Dopamine and norepinephrine pharmacology on the EDT. (a) Eticlopride dose-dependently decreased all animals' choice of HR trials across all blocks. (b) SCH23390 decreased choice of HR at the highest effort block. (c) Yohimbine appeared to have some minor effects on choice behavior, decreasing choice of the HR lever during the first two blocks, but this effect was not robust. (d) Atomoxetine did not affect choice on the EDT. Data are shown as the mean percent for each variable (±SEM).

Similar articles

See all similar articles

Cited by 32 articles

See all "Cited by" articles

Publication types

MeSH terms

Feedback