Pavlovian and Instrumental Conditioning and Their Mutual Influence in Major Depressive Disorder: The Mood and Emotional Learning Dynamics (MELD) Framework

Major Depressive Disorder (MDD) poses a significant burden for individuals and society. It compromises quality of life, disrupts productivity, and strains social relationships. Pavlovian and instrumental conditioning play an important role in psychopathology, yet the independent and joint contributions of these forms of emotional learning to depressed mood are not well understood. In particular, studies of Pavlovian conditioning and Pavlovian-instrumental transfer (PIT) in MDD are few. Studying PIT in MDD may improve our understanding of how emotional learning influences depressive symptoms that is more reflective of how Pavlovian and instrumental conditioning operate in the real world. In this review, we first provide a narrative summary of past research investigating emotional learning in MDD, including computational modeling approaches. Based on these findings, we then build on an existing theoretical framework characterizing emotional learning and decision making in depression by incorporating the potential influence of Pavlovian conditioned cues on instrumental behaviour in individuals experiencing depressed mood. Specifically, we propose that, in MDD, adaptive instrumental behaviours are interrupted by the exaggerated inhibitory influence of aversive Pavlovian cues and insufficiently invigorated by appetitive Pavlovian cues. We conclude with recommendations for future research investigating emotional learning in MDD.