Research reportIndividual differences in choice (in)flexibility but not impulsivity in the common marmoset: An automated, operant-behavior choice task

- We run a pilot for operant-choice behaviour in the common marmoset (Callithrix jacchus).
- Marmosets had choice between a Small & Soon (SS) vs a Large & Late (LL) food reward.
- Subjects were independently classified: “flexible” vs “non-flexible” and “maximizer” vs “non-maximizer”.
- Initially high LL preference and low motor impulsivity predicted flexibility of choices and better food payoff.
- Marmosets are suitable to investigate individual differences in flexibility by operant panels.

Individual differences in behavioural flexibility are a significant issue in human psychopathology as well as in its animal models. We aimed to investigate individual variations of operant-choice behaviour in the common marmoset (Callithrix jacchus), a small New World primate, using a new operant panel with two hand-poking holes.MethodsExperimental subjects (N = 16) were presented with a choice between a Small & Soon (SS) vs a Large & Late (LL) food reward. After extensive training (31 daily sessions with no delay, during which a basal, large-reward preference developed), the delay before release of LL was progressively increased (from 0 to 60 s, during 16 daily sessions; indifferent point at delay = 9 s). Subjects were classified as either “flexible” or “non-flexible”, respectively, based on a decrease (or not) in the preference for LL with increasing delays. Each subject was also classified as “maximizer” (or “non-maximizer”) based on capacity (or not) to maximize the food payoff as delay increased.ResultsUpon delays shorter than the indifferent point (<9 s), none of the subjects showed a shift from LL to SS, denoting a lack of delay-induced, cognitive impulsivity. Individual differences only emerged upon delays longer than the indifferent point (>9 s), when a preference shift could be interpreted as economically-driven. In general, a profile of few unrewarded hand-pokes in reaction to initial delays (i.e., a low motor impulsivity) and of clear-cut basal LL preference seemed to predict elevated flexibility of choices and better food payoff, which was typical of subjects classified as both “flexible & maximizer”.ConclusionThese results provide normative data on the marmosets, which can be used as a model for the investigation of 1) individual differences in behavioural flexibility, as well as 2) biological mechanisms rooted in our evolutionary history.