Home-cage testing of choice behaviour: proneness to risk in a gambling task

Pathological gambling (PG) is a mental health concern and is essentially an impulse-control disorder, associated with risk-taking and sensation-seeking traits. Psycho-genetic studies have revealed a role for the dopamine transporter (DAT). In animal models, many operant-behaviour tasks do test the lack of self-control abilities and / or impulsive decision-making. Among these, the probabilistic-delivery (PD) task is based on choice between a “Large and Luck-Linked” (LLL) or a “Small and Sure” (SS) reward. During testing, the level of probability (“p”) governing successful (or omitted) LLL delivery is decreased progressively, thus implementing a “binge” but rarefied event. Using a PD task in rats, we demonstrated previously the emergence of distinct sub-populations: “risk-prone” rats maintained a significant attraction for LLL, while “conservative” ones developed a clear preference for SS. Here, we describe a pilot study with a PD task, aimed to identify a phenotype of risk proneness in animal models, adapted to home-cage testing. Indeed, recent literature proposes that testing animals in their home cage avoids the distress of being handled daily, moved to a novel apparatus in a separate room, and given a limited time-window for data collection. Thus, our testing apparatus consisted of home-cage operant panels, placed in the rats’ home cage. Animals were trained to feed by operating this panel through nosepoking. Daily sessions were run for 12h (8.00 pm to 8.00 am) during the dark phase of the cycle. The whole protocol lasted ten days in total. Training phase (three sessions at p = 50%) allowed subjects to reach a significant preference for LLL, then “p” was decreased progressively until and beyond the indifferent point, i.e. when LLL becomes a sub-optimal choice. As expected, rats showed only a slight reduction in their LLL preference, but did not show any significant change of strategy and never developed a clear preference for SS, even beyond the indifferent point. This is relevant for theories of behavioural economics, since they could have gained more food with less work had they chosen to shift towards a SS choice strategy. Present pilot experiment shows in principle that it is possible to measure gambling behaviour in a home-cage setting, and future experiments are directed at further validating this approach.