An occasion for reflection: Pavlovian modulation of conditioned responding by interoceptive drug stimuli

Nearly 100 years ago, Ivan Pavlov's research into learning processes provided a framework for understanding how the brain makes behaviorally impactful associations between events. His seminal findings on excitatory and inhibitory conditioning established the scientific and conceptual foundation for the later discovery of Pavlovian occasion setting. That is, a higher-order association that modulates whether or not a conditioned stimulus will evoke a conditioned response-feature positive and feature negative occasion setters, respectively. While much of this research has used exteroceptive stimuli (tone, lights), interoceptive stimuli (intoxication, hunger) can also acquire occasion setting functions. Research using the drug discriminated goal-tracking (DDGT) task demonstrates that interoceptive drug stimuli serve reliably as occasion setters. A wide range of drug stimuli across pharmacological classes function as occasion setters (e.g., nicotine, chlordiazepoxide, morphine) in the DDGT task. Moreover, interoceptive drug occasion setters exhibit similar characteristics as exteroceptive occasion setters. These include resistance to simple extinction procedures, generalization across stimulus (drug) class with shared function as an occasion setters, and a drug feature-negative occasion setter acquiring conditioned inhibitory effects. We explore future avenues of inquiry utilizing the DDGT task to expand our understanding of occasion setting. We highlight methodological strengths that recommend the DDGT task for probing the neuropharmacological and neuroanatomical mechanisms of drug occasion setters. Pavlov recognized the importance of interoception, and the role conditioning processes play in health and well-being. We invite readers to consider how their research intersects with the topic of interoceptive conditioning. By working together, we can build our understanding of basic interoceptive Pavlovian conditioning processes and realize the solutions this knowledge holds to societal issues.