Background Experimental extinction serves as a model for psychiatric treatments based on associative learning. However, the effects of extinction are often transient, as evidenced by post-extinction return of defensive behaviors. From a therapeutic perspective, an inherent problem with extinction may be that mere omission of threat is not sufficient to reduce future threat uncertainty. The current study tested an augmented form of extinction that replaced- rather than merely omitted- expected threat outcomes with novel non-threat outcomes, with the goal of reducing post-extinction return of defensive behaviors. Methods Thirty-two healthy male Sprague-Dawley rats and 47 human adults underwent threat conditioning to a conditioned stimulus paired with an electrical shock. Subjects then underwent a standard extinction protocol with shock omitted, or an augmented extinction protocol wherein the shock was replaced by a surprising tone. Tests of post-extinction recovery occurred 24 hours later in the absence of the tone. Results Replacing the shock with a novel non-threat outcome, as compared to shock omission, reduced post-extinction recovery (freezing in rats and anticipatory skin conductance responses in humans) when tested 24 hours later. Self-reported intolerance of uncertainty was positively correlated with recovery following standard extinction in humans, providing new evidence that post-extinction recovery is related to sensitivity to future threat uncertainty. Conclusions These findings provide cross-species evidence of a novel strategy to enhance extinction that may have broad implications for how to override associative learning that has become maladaptive, and offer a simple technique that could be straightforwardly adapted and implemented in clinical situations.

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It has been suggested that there are two distinct and parallel mechanisms for controlling instrumental behavior in mammals: goal-directed actions and habits. To gain an understanding of how these two systems interact to control behavior, it is essential to characterize the mechanisms by which the balance between these systems is influenced by experience. Studies in rodents have shown that the amount of training governs the relative expression of these two systems: Behavior is goal-directed following moderate training, but the more extensively an instrumental action is trained, the more it becomes habitual. It is less clear whether humans exhibit similar training effects on the expression of goal-directed and habitual behavior, as human studies have reported contradictory findings. To tackle these contradictory findings, we formed a consortium, where four laboratories undertook a preregistered experimental induction of habits by manipulating the amount of training. There was no statistical evidence for a main effect of the amount of training on the formation and expression of habits. However, exploratory analyses suggest a moderating effect of the affective component of stress on the impact of training over habit expression. Participants who were lower in affective stress appeared to be initially goal-directed, but became habitual with increased training, whereas participants who were high in affective stress were already habitual even after moderate training, thereby manifesting insensitivity to overtraining effects. Our findings highlight the importance of the role of moderating variables such as individual differences in stress and anxiety when studying the experimental induction of habits in humans.

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23Researchers have exerted tremendous efforts to empirically study how habits form and dominate 24 at the expense of deliberation, yet we know very little about breaking these rigid habits to restore 25 goal-directed control. In a three-experiment study, we first illustrate a novel approach of 26 studying well-learned habits, in order to effectively demonstrate habit disruption. In Experiment 27 1, we use a Go/NoGo task with familiar color-response associations to demonstrate outcome-28 insensitivity when compared to novel, more flexible associations. Specifically, subjects perform 29 more accurately when the required mapping is the familiar association of green-Go/red-NoGo 30 than when it is red-Go/green-NoGo, confirming outcome-insensitive, habitual control. As a 31 control condition, subjects show equivalent performance with unfamiliar color-response 32 mappings (using the colors blue and purple mapped to Go and NoGo responses). Next, in 33 Experiments 2 and 3, we test a motivation-based feedback manipulation in varying magnitudes 34 (i.e., performance feedback with and without monetary incentives) to break the well-established 35 habits elicited by our familiar stimuli. We find that although performance feedback prior to the 36 contingency reversal test is insufficient to disrupt outcome-insensitivity in Experiment 2, a 37 combination of performance feedback and monetary incentive is able to restore goal-directed 38 control in Experiment 3, effectively breaking the habits. As the first successful demonstration of 39 well-learned habit disruption in the laboratory, these findings provide new insights into how we 40 execute and modify habits, while fostering new and translational research avenues that may be 41 applicable to treating habit-based pathologies. 42 43 44 45 Providing opportunities for performance tracking and administering other forms of 131 performance-based feedback (e.g., primary and secondary rewards) have been used extensively 132 in enhancing behavioral output [22,23]. For instance, the delivery of performance tracking 133 information combined with a monetary reward successfully improved performance on a visual 134 task [23]. A combination of primary and secondary rewards (e.g., juice and monetary incentives) 135 has also been documented to improve goal-directed performance on a cued task-switching 136 paradigm via motivational enhancement [24]. The promise of a future reward contingent on 137