Dopaminergic control of preference for reward maximization and reward unpredictability during free choice.

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In order to improve their chance of survival, animals must maximise food intake (energy gain). However, in some circumstances, mammals and birds seem to adopt a suboptimal seeking strategy, preferring an unpredictable food option which provides a lower reward rate. The reasons for this irrational choice are not clearly established, notably because most experimental procedures used have not attempted to study the effects of reward maximisation and of reward unpredictability separately. For example, comparing performance on a fixed schedule and a variable schedule with an equivalent mean (as often reported) brings little information about the motivation of the animal. Does it preferentially choose the variable schedule because intrigued by unpredictability or because food can be obtained sooner or because of a combination of these two components? In fact, maximisation and unpredictability might be combined in food seeking, as they are in human gambling: the individuals try to maximize gains, but unpredictability is necessary to hold their interest in the task. In this project, I suggest five experiments whose aim is twofold: (1) understanding the extent to which food maximization and food unpredictability can control behavioural choices in a free-choice task, and (2) showing how dopamine determines sensitivity to reward maximization and reward unpredictability. Indeed, dopamine is a neurotransmitter chiefly recruited by rewards and conditioned cues, but also very sensitive to the unpredictability of cue-reward associations. I plan to use pigeons as animal model since a large body of literature is devoted to processes of choice in pigeons while at the same time the relevant neurobiological mechanisms are less understood in birds. Thus, the results of the present application would not only generate important results for the present study but could also provide insights about invariant mechanisms of reward-associated behaviour across vertebrate classes.