Abstract
Pavlovian-to-instrumental transfer (PIT) is an effect whereby a classically conditioned stimulus (CS) enhances ongoing instrumental responding. PIT has been extensively studied with appetitive conditioning but barely at all with aversive conditioning. Although it's been argued that conditioned suppression is a form of aversive PIT, this effect is fundamentally different from appetitive PIT because the CS suppresses, instead of facilitates, responding. Five experiments investigated the importance of a variety of factors on aversive PIT in a rodent Sidman avoidance paradigm in which ongoing shuttling behavior (unsignaled active avoidance or USAA) was facilitated by an aversive CS. Experiment 1 demonstrated a basic PIT effect. Experiment 2 found that a moderate amount of USAA extinction produces the strongest PIT with shuttling rates best at around 2 responses per minute prior to the CS. Experiment 3 tested a protocol in which the USAA behavior was required to reach the 2-response per minute mark in order to trigger the CS presentation and found that this produced robust and reliable PIT. Experiment 4 found that the Pavlovian conditioning US intensity was not a major determinant of PIT strength. Experiment 5 demonstrated that if the CS and US were not explicitly paired during Pavlovian conditioning, PIT did not occur, showing that CS-US learning is required. Together, these studies demonstrate a robust, reliable and stable aversive PIT effect that is amenable to analysis of neural circuitry.
Highlights
Much has been learned about the neural basis of aversive conditioning through studies of Pavlovian threat conditioning (PTC) (e.g., Maren, 2005; Johansen et al, 2011a,b)
Aversive Pavlovian conditioned stimulus (CS) can facilitate unsignaled Sidman active avoidance (USAA) rates in rats. The magnitude of this facilitation was modest with the current protocol, perhaps because USAA rates were near ceiling at the outset of Pavlovian-toinstrumental transfer (PIT) testing because of shocks early in the PIT test session that were meant to facilitate warm-up of the USAA response
Pilot experiments suggested that testing PIT once per session produced more reliable effects, only one CS presentation was delivered in each PIT test session
Summary
Much has been learned about the neural basis of aversive conditioning through studies of Pavlovian threat (fear) conditioning (PTC) (e.g., Maren, 2005; Johansen et al, 2011a,b). Most often the relation between aversive Pavlovian and instrumental learning is studied using avoidance conditioning (e.g., Sarter and Markowitsch, 1985; Gabriel et al, 2003; Choi et al, 2010) In such tasks the Pavlovian and instrumental training are intermixed and it becomes procedurally difficult to separate the effects of the Pavlovian CS on the instrumental response. Because Pavlovian and instrumental training occur separately, PIT provides an experimental procedure in which the effects of conditioned motivation can be evaluated in isolation from primary reinforcement processes. Maintaining these psychological processes as distinct is important for understanding how they are mediated by the brain
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