Anselme & Güntürkün (A&G) introduce the concept of “incentive hope” to explain foraging in animals when food supply is uncertain. Uncertainty-induced dopamine release invigorates pursuit of cues signaling food availability, when the association between cues and food is unreliable (cf. Fiorillo et al. Reference Fiorillo, Tobler and Schultz2003). Incentive hope differs from incentive salience because it entails pursuit of remote rewards and is evoked specifically by uncertainty, whereas salience mediates approach of proximal rewards (Berridge Reference Berridge2007).
A&G advance several novel ideas. First, Pavlovian autoshaping is cited to explain how uncertainty promotes foraging. In autoshaping, animals persist in seeking a reward when a conditioned stimulus (CS) is present both when food (unconditioned stimulus [UCS]) is delivered and when it is withheld (Brown & Jenkins Reference Brown and Jenkins1968). Autoshaped responses persist despite prolonged absence of reward, indicating they are under Pavlovian rather than instrumental control. A&G note that animals foraging under uncertainty hoard more food and store more fat than animals foraging when food is reliably available (Pravosudov & Grubb Reference Pravosudov and Grubb1997). Thus, uncertainty-induced foraging represents an evolutionary advantage to individuals that do this most effectively. In autoshaping, these individuals are called sign-trackers, and their behavior differs reliably from that of animals whose seeking is more instrumental. The latter group, goal-trackers, use CSs primarily to facilitate access to food. In contrast, sign-trackers find CSs rewarding in their own right: They seek and interact with them more than UCSs that they signal (Robinson & Flagel Reference Robinson and Flagel2009). Second, incentive hope entails the recruitment, during uncertainty, of glucocorticoids, which in turn activate dopamine (Barrot et al. Reference Barrot, Marinelli, Abrous, Rougé-Pont, Le Moal and Piazza2000). Much like a car's accelerator, glucocorticoids permit the transmission to work harder while signaling availability of fuel for expenditure when dopamine-mediated reward seeking occurs. Third, the incentive hope model asserts that invigoration of reward seeking during uncertainty is not subjectively reinforcing. It is strictly an adaptive response born of necessity. When predictable and unpredictable rewards are available, animals choose the former (e.g., Smith & Zentall Reference Smith and Zentall2016).
A&G extrapolate from foraging in animals under uncertainty to humans under unpredictable living conditions, suggesting that incentive hope may explain excessive-compulsive behaviors such as substance abuse, pathological gambling, and overeating and obesity. The correspondence with overeating is straightforward. The correspondence with substance abuse and pathological gambling is less so. In the case of gambling, the authors assert that casinos are essentially human autoshaping boxes. Like autoshaped rats, gamblers persist despite ongoing losses because of the presence of CSs (e.g., lights, bells), whose association with reward delivery is uncertain. Although most people gamble for some time and then quit, typically when their money runs out, a few persist despite ongoing losses, a behavior called “chasing” (Toce-Gerstein et al. Reference Toce-Gerstein, Gerstein and Volberg2003). These pathological gamblers have presumably fallen prey to autoshaping.
Incentive hope is a valuable extension of the incentive salience concept as it explains why animals pursue rewards that are physically absent. The linkage with autoshaping is novel and defines a potential mechanism to explain chasing in pathological gamblers. The putative facilitatory role of glucocorticoids helps explain how stress translates into reward seeking under uncertainty and aligns with empirical evidence of deficient basal cortisol transmission in pathological gamblers (Zack et al. Reference Zack, Boileau, Payer, Chugani, Lobo, Houle, Wilson, Warsh and Kish2015). Targeting neural substrates of autoshaping (e.g., dorsomedial striatum; Torres et al. Reference Torres, Glueck, Conrad, Moron and Papini2016) may also improve interventions for maladaptive reward seeking under uncertainty in humans.
Along with these many strengths there are a few shortcomings. First, as A&G note, delay of reward may be even more important than uncertainty as a driver of food seeking (Mazur Reference Mazur, Commons, Mazur, Nevin and Rachlin1987). If an animal experiences a 1-week lack of food at exactly 2-month intervals, it may be more inclined to hoard and store fat than an animal that encounters food at irregular intervals of a few hours. Thus, of the two motivating factors, uncertainty and delay, fear of starvation may be a more important motivator than incentive hope. Second, the adaptive phenotype in A&G's model is a sign-tracker. Sign-trackers engage primarily with CSs, not UCSs (Robinson & Flagel Reference Robinson and Flagel2009). Thus, sign-trackers may be more interested in, and interact more extensively with, a particular species of tree (CS) than with the eggs (UCS) that are likely to be nested there. Under these conditions, goal-trackers may fare better in evolutionary terms simply by following sign-trackers to a location where they can usurp the food. Third, incentive hope predicts maximally vigorous food seeking and fat storage under conditions of food uncertainty. This does not explain why copious food supply and reliable CSs for food (e.g., restaurants) coincide with the current epidemic of obesity (cf. Vucetic & Reyes Reference Vucetic and Reyes2010). Uncertainty of food predicts food seeking and hoarding in nature. This is not tantamount to uncertainty in general – the anxiety of modern society – as a driver of food seeking. At best, food seeking in this scenario is a form of displacement or adjunctive behavior rather than a direct response to unpredictable food. Fourth, the idea that reward seeking under uncertainty is strictly utilitarian does not translate well to gambling. Social gamblers willingly spend time, energy, and resources to access unpredictable rewards in casinos. They also display numerous behaviors indicative of pleasure. Players at a roulette table often display or verbalize intense anticipatory excitement (Goudriaan & Clark Reference Goudriaan, Clark and Miller2013). Similarly, slot machine gamblers report eager anticipation of winning (Ladouceur et al. Reference Ladouceur, Sevigny, Blaszczynski, O'Connor and Lavoie2003). These expressions of positive arousal may correspond loosely to 50-kHz vocalizations of rodents when amphetamine is injected into their nucleus accumbens (Burgdorf et al. Reference Burgdorf, Knutson, Panksepp and Ikemoto2001). In addition, pathological gamblers are strongly driven by the desire to win (Lee et al. Reference Lee, Chae, Lee and Kim2007). They chase losses precisely because they hope for a win that will erase their losses, not because of an automatized Pavlovian response, although Pavlovian factors may be involved. A key reason why uncertainty is pleasurable in gambling, unlike foraging, is that the potential reward far outweighs any lost investment or opportunity foregone (Gainsbury et al. Reference Gainsbury, Suhonen and Saastamoinen2014). As long as a jackpot awaits, every trial is suffused with eager anticipation.
In sum, incentive hope provides a novel explanation for foraging. However, the factors that mediate foraging under uncertainty in nature do not correspond fully to excessive-compulsive behaviors in humans. Uncertainty is a powerful driving force in nature and in some human environments. I believe incentive hope is most useful as a heuristic to guide inquiry and that foraging under uncertainty in animals is an analogy rather than a direct counterpart to human excessive-compulsive behavior.
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Anselme & Güntürkün (A&G) introduce the concept of “incentive hope” to explain foraging in animals when food supply is uncertain. Uncertainty-induced dopamine release invigorates pursuit of cues signaling food availability, when the association between cues and food is unreliable (cf. Fiorillo et al. Reference Fiorillo, Tobler and Schultz2003). Incentive hope differs from incentive salience because it entails pursuit of remote rewards and is evoked specifically by uncertainty, whereas salience mediates approach of proximal rewards (Berridge Reference Berridge2007).
A&G advance several novel ideas. First, Pavlovian autoshaping is cited to explain how uncertainty promotes foraging. In autoshaping, animals persist in seeking a reward when a conditioned stimulus (CS) is present both when food (unconditioned stimulus [UCS]) is delivered and when it is withheld (Brown & Jenkins Reference Brown and Jenkins1968). Autoshaped responses persist despite prolonged absence of reward, indicating they are under Pavlovian rather than instrumental control. A&G note that animals foraging under uncertainty hoard more food and store more fat than animals foraging when food is reliably available (Pravosudov & Grubb Reference Pravosudov and Grubb1997). Thus, uncertainty-induced foraging represents an evolutionary advantage to individuals that do this most effectively. In autoshaping, these individuals are called sign-trackers, and their behavior differs reliably from that of animals whose seeking is more instrumental. The latter group, goal-trackers, use CSs primarily to facilitate access to food. In contrast, sign-trackers find CSs rewarding in their own right: They seek and interact with them more than UCSs that they signal (Robinson & Flagel Reference Robinson and Flagel2009). Second, incentive hope entails the recruitment, during uncertainty, of glucocorticoids, which in turn activate dopamine (Barrot et al. Reference Barrot, Marinelli, Abrous, Rougé-Pont, Le Moal and Piazza2000). Much like a car's accelerator, glucocorticoids permit the transmission to work harder while signaling availability of fuel for expenditure when dopamine-mediated reward seeking occurs. Third, the incentive hope model asserts that invigoration of reward seeking during uncertainty is not subjectively reinforcing. It is strictly an adaptive response born of necessity. When predictable and unpredictable rewards are available, animals choose the former (e.g., Smith & Zentall Reference Smith and Zentall2016).
A&G extrapolate from foraging in animals under uncertainty to humans under unpredictable living conditions, suggesting that incentive hope may explain excessive-compulsive behaviors such as substance abuse, pathological gambling, and overeating and obesity. The correspondence with overeating is straightforward. The correspondence with substance abuse and pathological gambling is less so. In the case of gambling, the authors assert that casinos are essentially human autoshaping boxes. Like autoshaped rats, gamblers persist despite ongoing losses because of the presence of CSs (e.g., lights, bells), whose association with reward delivery is uncertain. Although most people gamble for some time and then quit, typically when their money runs out, a few persist despite ongoing losses, a behavior called “chasing” (Toce-Gerstein et al. Reference Toce-Gerstein, Gerstein and Volberg2003). These pathological gamblers have presumably fallen prey to autoshaping.
Incentive hope is a valuable extension of the incentive salience concept as it explains why animals pursue rewards that are physically absent. The linkage with autoshaping is novel and defines a potential mechanism to explain chasing in pathological gamblers. The putative facilitatory role of glucocorticoids helps explain how stress translates into reward seeking under uncertainty and aligns with empirical evidence of deficient basal cortisol transmission in pathological gamblers (Zack et al. Reference Zack, Boileau, Payer, Chugani, Lobo, Houle, Wilson, Warsh and Kish2015). Targeting neural substrates of autoshaping (e.g., dorsomedial striatum; Torres et al. Reference Torres, Glueck, Conrad, Moron and Papini2016) may also improve interventions for maladaptive reward seeking under uncertainty in humans.
Along with these many strengths there are a few shortcomings. First, as A&G note, delay of reward may be even more important than uncertainty as a driver of food seeking (Mazur Reference Mazur, Commons, Mazur, Nevin and Rachlin1987). If an animal experiences a 1-week lack of food at exactly 2-month intervals, it may be more inclined to hoard and store fat than an animal that encounters food at irregular intervals of a few hours. Thus, of the two motivating factors, uncertainty and delay, fear of starvation may be a more important motivator than incentive hope. Second, the adaptive phenotype in A&G's model is a sign-tracker. Sign-trackers engage primarily with CSs, not UCSs (Robinson & Flagel Reference Robinson and Flagel2009). Thus, sign-trackers may be more interested in, and interact more extensively with, a particular species of tree (CS) than with the eggs (UCS) that are likely to be nested there. Under these conditions, goal-trackers may fare better in evolutionary terms simply by following sign-trackers to a location where they can usurp the food. Third, incentive hope predicts maximally vigorous food seeking and fat storage under conditions of food uncertainty. This does not explain why copious food supply and reliable CSs for food (e.g., restaurants) coincide with the current epidemic of obesity (cf. Vucetic & Reyes Reference Vucetic and Reyes2010). Uncertainty of food predicts food seeking and hoarding in nature. This is not tantamount to uncertainty in general – the anxiety of modern society – as a driver of food seeking. At best, food seeking in this scenario is a form of displacement or adjunctive behavior rather than a direct response to unpredictable food. Fourth, the idea that reward seeking under uncertainty is strictly utilitarian does not translate well to gambling. Social gamblers willingly spend time, energy, and resources to access unpredictable rewards in casinos. They also display numerous behaviors indicative of pleasure. Players at a roulette table often display or verbalize intense anticipatory excitement (Goudriaan & Clark Reference Goudriaan, Clark and Miller2013). Similarly, slot machine gamblers report eager anticipation of winning (Ladouceur et al. Reference Ladouceur, Sevigny, Blaszczynski, O'Connor and Lavoie2003). These expressions of positive arousal may correspond loosely to 50-kHz vocalizations of rodents when amphetamine is injected into their nucleus accumbens (Burgdorf et al. Reference Burgdorf, Knutson, Panksepp and Ikemoto2001). In addition, pathological gamblers are strongly driven by the desire to win (Lee et al. Reference Lee, Chae, Lee and Kim2007). They chase losses precisely because they hope for a win that will erase their losses, not because of an automatized Pavlovian response, although Pavlovian factors may be involved. A key reason why uncertainty is pleasurable in gambling, unlike foraging, is that the potential reward far outweighs any lost investment or opportunity foregone (Gainsbury et al. Reference Gainsbury, Suhonen and Saastamoinen2014). As long as a jackpot awaits, every trial is suffused with eager anticipation.
In sum, incentive hope provides a novel explanation for foraging. However, the factors that mediate foraging under uncertainty in nature do not correspond fully to excessive-compulsive behaviors in humans. Uncertainty is a powerful driving force in nature and in some human environments. I believe incentive hope is most useful as a heuristic to guide inquiry and that foraging under uncertainty in animals is an analogy rather than a direct counterpart to human excessive-compulsive behavior.