How do stimuli steer our choices between courses of action?

What is it about?

Stimuli that predict events can elicit specific actions that have produced those same events in the past. For example, an advertisement for a particular food can prompt behaviours that lead to the acquisition of that food. This stimulus control over choice behaviour may be investigated in the laboratory using so-called Pavlovian-to-instrumental transfer tasks in humans and non-human animals. Typically these tasks involve the experimental subject learning Stimulus-Outcome (S-O) associations using Pavlovian conditioning (e.g. tone-food), and separately learning Response-Outcome (R-O) associations using instrumental conditioning (e.g. lever press-food), then testing the subject by presenting the stimulus alongside a choice between multiple instrumental responses. Such conditioned stimuli typically prompt the subject to choose a response that produces the same outcome as that which is predicted by the stimulus. This is the Pavlovian-to-instrumental transfer effect. The question of when Pavlovian-to-instrumental transfer actually occurs remains under debate, and is key in understanding the mechanisms underlying the phenomenon. We aimed to gather additional evidence to determine whether transfer is driven by recalling the specific relevant outcome at the time of testing (e.g. tone-food-lever press), or if outcome-independent associations (i.e. Stimulus-Response) form during training, allowing conditioned stimuli to directly elicit specific instrumental behaviour (e.g. tone-lever press). By identifying an experimental manipulation that successfully undermines the integrity of Pavlovian associations in rats, we demonstrate that the Pavlovian-to-instrumental transfer effect is disrupted when S-O associations were intact during instrumental training, but degraded prior to testing. These findings add to the growing body of evidence suggesting that conditioned stimuli guide actions via the real-time integration of multiple associative memories.

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Photo by Nikolett Emmert on Unsplash

Photo by Nikolett Emmert on Unsplash

Why is it important?

Understanding how stimuli control our actions has important implications for our models of learning and decision-making. Our results provide novel insights into the fundamental processes of interaction between predictive information and action control and have implications for harnessing strategies for behavioural modification and understanding how unhelpful or unwanted stimulus-driven behaviours may emerge.

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