Effects of Early-Life Stress on Actions, Habits, and the Neural Systems Supporting Instrumental Behavior
Factors contributing to the formation of habits, defined as the stimulus-response associations that form the basis of much human and animal behavior, are not well understood, and although habits are believed to underlie many negative health behaviors such as addictions, the extent to which findings from animal research on habits apply in the human is largely unknown. In Study 1 (Chapter 2), we conducted two experiments on appetitive habit formation in adults with a history of early-life stress. Using the size of the partial reinforcement extinction effect as a measure of goal-directed versus habit behavior, we found evidence of increased habit behavior in people who reported a history of early-life stress, and this effect appeared to be enhanced by the presence of distraction. In Study 2 (Chapter 3), we conducted two experiments on avoidance habit formation in this population. People with a history of early-life stress exhibited enhanced avoidance habits as measured by persistence of learned behaviors after outcome devaluation. Finally, in Study 3 (Chapter 4), we conducted a meta-analysis of fMRI studies on human habit responding to assess the contributions of striatal subregions to habit behavior. We found that activation patterns varied based on the task that was used (probabilistic classification, maze navigation, outcome devaluation, sequential decision, or motor sequence learning), with differences observed along both the anterior-posterior and medial-lateral axes. Chapter 5 summarizes the findings and makes suggestions for future research.