title: Individual differences in choice (in)flexibility but not impulsivity in the common marmoset: an automated, operant-behavior choice task.
abstract: 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.
  
  
  METHODS
  Experimental 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.
  
  
  RESULTS
  Upon delays shorter than the indifferent point (<9s), 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".
  
  
  CONCLUSIONS
  These 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.
authors.affiliation: Section of Behavioral Neuroscience, Dept. of Cell Biology & Neurosciences, Istituto Superiore di Sanità, Rome, Italy. Electronic address: walter.adriani@iss.it.
authors.forename: Walter
authors.initials: W
authors.lastname: Adriani
authors.forename: Chiara
authors.initials: C
authors.lastname: Romani
authors.forename: Arianna
authors.initials: A
authors.lastname: Manciocco
authors.forename: Augusto
authors.initials: A
authors.lastname: Vitale
authors.forename: Giovanni
authors.initials: G
authors.lastname: Laviola
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D002144:Callithrix; D002755:Choice Behavior / Q000502:physiology*; D003216:Conditioning, Operant / Q000502:physiology*; D005260:Female; D007175:Impulsive Behavior / Q000503:physiopathology*; D007206:Individuality; D008297:Male; D012055:Reinforcement Schedule; D012201:Reward
keywords: Callithrix jacchus; Decision-making; Operant choice; Payoff; Self-control