Can Slot-Machine Reward Schedules Induce Gambling Addiction in Rats?

Post-loss speeding or post-win slowing? An empirical note on the interpretation of decision-making time as a function of previous outcome

Differences in response time following previous losses relative to previous wins are robust observations in behavioural science, often attributed to an increased (or decreased) degree of cognitive control exerted after negative feedback, hence, post-loss slowing (or post-loss speeding). This presumes that the locus of this effect resides in the specific modulation of decision time following negative outcomes. Across two experiments, I demonstrate how the use of absolute rather than relative processing speeds, and the sensitivity of processing speeds in response to specific experimental manipulations (Experiment 1: win rate, Experiment 2: feedback), provide clarity as to the relative weighting of post-win and post-loss states in determining these behavioural effects. Both experiments show that the speeding or slowing of decision-time is largely due to the flexibility generated by post-win cognitive states. Given that post-loss speeding may actually represent post-win slowing, conclusions regarding the modulation of decision-making time as a function of previous outcomes need to be more carefully considered.

Translating concepts of risk and loss in rodent models of gambling and the limitations for clinical applications

Gambling involves placing something of value at risk in exchange for the opportunity to potentially gain something of greater value in return. A variety of gambling paradigms have been designed to study the maladaptive decision-making that underlies problematic gambling. Central to these gambling models are the definitions of "risk" and "loss", especially when translating the results from rodent studies to clinical applications. Risk and loss are not mutually exclusive but rather share some overlap. With careful interpretation and consideration of the limitations of these behavioral paradigms, results from rodent models may provide insights into the neurobiology of risky decision-making that leads to problematic gambling in humans.

Maladaptive consequences of repeated intermittent exposure to uncertainty

Recently we reported that nucleus accumbens (NAcc) dopamine (DA) tracks uncertainty during operant responding for non-caloric saccharin. We also showed that repeated intermittent exposure to this uncertainty, like exposure to drugs of abuse, leads to sensitization of the locomotor and NAcc DA effects of amphetamine and promotes the subsequent self-administration of the drug. Here we review these findings together with others showing that NAcc glutamate signaling is similarly affected by uncertainty. Extracellular levels of glutamate in this site also track uncertainty in a task in which nose poking for saccharin on an escalating variable ratio schedule of reinforcement is associated with progressively increasing variance between performance of the operant and payout. Furthermore, sensitized behavioral responding to and for amphetamine following exposure to uncertainty is accompanied by increased levels of Ca2+/calmodulin-dependent protein kinase II (CaMKII) and protein kinase C (PKC) phosphorylation as well as altered protein levels of the transcription factor ∆FosB (increased) and glutamate transporter 1 (GLT1; decreased) in NAcc tissues. Notably, phosphorylation by CaMKII and PKC regulates AMPA receptor trafficking and function in this site, is elevated following psychostimulant exposure, and is necessary for the expression of enhanced drug taking. Increased ∆FosB and decreased GLT1 levels are observed following psychostimulant exposure, are associated with increased drug taking and seeking, and are known to modulate AMPA receptors and extracellular glutamate levels respectively. These adaptations in glutamate transmission as well as those observed with DA following repeated intermittent exposure to uncertainty are similar to those produced by exposure to abused drugs. Together, they point to the recruitment of both DA and glutamate signaling pathways in the NAcc in both drug and behavioral addictions. As uncertainty is central to games of chance, these findings have particular relevance for gambling disorders known to exhibit comorbidity with drug abuse.