Original Article

Neuropsychopharmacology (2012) 37, 1825–1837; doi:10.1038/npp.2012.30; published online 28 March 2012

Sensitivity to Cognitive Effort Mediates Psychostimulant Effects on a Novel Rodent Cost/Benefit Decision-Making Task

Paul J Cocker1,2, Jay G Hosking1,2, James Benoit1 and Catharine A Winstanley1

1Department of Psychology, University of British Columbia, Vancouver, British Columbia, Canada

Correspondence: JG Hosking or Dr CA Winstanley, Department of Psychology, University of British Columbia, 2136 West Mall, Vancouver, BC V6T 1Z4, Canada, Tel: +1 604 827 5083, Fax: +1 604 822 6923, E-mail: jayhosking@psych.ubc.ca or cwinstanley@psych.ubc.ca

2These authors contributed equally to this work

Received 19 November 2011; Revised 13 February 2012; Accepted 17 February 2012
Advance online publication 28 March 2012

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Abstract

Amotivational states and insufficient recruitment of mental effort have been observed in a variety of clinical populations, including depression, traumatic brain injury, post-traumatic stress disorder, and attention deficit hyperactivity disorder. Previous rodent models of effort-based decision making have utilized physical costs whereas human studies of effort are primarily cognitive in nature, and it is unclear whether the two types of effortful decision making are underpinned by the same neurobiological processes. We therefore designed a novel rat cognitive effort task (rCET) based on the 5-choice serial reaction time task, a well-validated measure of attention and impulsivity. Within each trial of the rCET, rats are given the choice between an easy or hard visuospatial discrimination, and successful hard trials are rewarded with double the number of sugar pellets. Similar to previous human studies, stable individual variation in choice behavior was observed, with ‘workers’ choosing hard trials significantly more than their ‘slacker’ counterparts. Whereas workers ‘slacked off’ in response to administration of amphetamine and caffeine, slackers ‘worked harder’ under amphetamine, but not caffeine. Conversely, these stimulants increased motor impulsivity in all animals. Ethanol did not affect animals' choice but invigorated behavior. In sum, we have shown for the first time that rats are differentially sensitive to cognitive effort when making decisions, independent of other processes such as impulsivity, and these baseline differences can influence the cognitive response to psychostimulants. Such findings could inform our understanding of impairments in effort-based decision making and contribute to treatment development.

Keywords:

cognitive effort; cost/benefit decision making; individual differences; amphetamine; caffeine; rat

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