Individual differences in impulsive and risky choice are key risk factors for a variety of maladaptive behaviors such as drug abuse, gambling, and obesity. In our rat model, ordered individual differences are stable across choice parameters and months of testing, and span a broad spectrum, suggesting that rats, like humans, exhibit trait-level impulsive and risky choice behaviors. In addition, impulsive and risky choices are highly correlated, suggesting a degree of correspondence between these two traits. An examination of the underlying cognitive mechanisms has suggested an important role for timing processes in impulsive choice. In addition, in an examination of genetic factors in impulsive choice, the Lewis rat strain emerged as a possible animal model for studying disordered impulsive choice, with this strain demonstrating deficient delay processing. Early rearing environment also affected impulsive behaviors, with rearing in an enriched environment promoting adaptable and more self-controlled choices. The combined results with impulsive choice suggest an important role for timing and reward sensitivity in moderating impulsive behaviors. Relative reward valuation also affects risky choice, with manipulation of objective reward value (relative to an alternative reference point) resulting in loss chasing behaviors that predicted overall risky choice behaviors. The combined results are discussed in relation to domain-specific versus domain-general subjective reward valuation processes and the potential neural substrates of impulsive and risky choice.
Keywords: impulsive choice; risky choice; discounting; individual differences; ratImpulsive choice is measured by presenting a choice between a smaller reward that is available sooner (the SS) and a larger reward that is available later (the LL). Thus, the impulsive choice paradigm pits reward magnitude against delay to reward by essentially asking whether an individual is willing to wait longer to receive a better outcome (Mazur, 1987(Mazur, , 2007. Impulsive choice is indicated by preferences for the SS, particularly when those choices lead to less overall reward earning, and are thus maladaptive, whereas choices of the LL (when it is more objectively valuable) are indicative of greater self-control. Individual differences in impulsive choice are associated with numerous maladaptive behaviors and disorders such as: attention deficit hyperactivity disorder (ADHD; Barkley, Edwards, Laneri, Fletcher, & Metevia, 2001;Solanto et al., 2001;Sonuga-Barke, 2002;Sonuga-Barke, Taylor, Sembi, & Smith, 1992), pathological gambling (Alessi & Petry, 2003;MacKillop et al., 2011;Reynolds, Ortengren, Richards, & de Wit, 2006), obesity (Davis, Patte, Curtis, & Reid, 2010), and substance abuse (Bickel & Marsch, 2001). Additionally, impulsive choice has also been posited as a primary risk factor (MacKillop et al., 2011;Verdejo-García, Lawrence, & Clark, 2008) and
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