Maintained goal-directed control with overtraining on ratio schedules

Characterizing Human Habits in the Lab

Habits pose a fundamental puzzle for those aiming to understand human behavior. They pervade our everyday lives and dominate some forms of psychopathology but are extremely hard to elicit in the lab. In this Registered Report, we developed novel experimental paradigms grounded in computational models, which suggest that habit strength should be proportional to the frequency of behavior and, in contrast to previous research, independent of value. Specifically, we manipulated how often participants performed responses in two tasks varying action repetition without, or separately from, variations in value. Moreover, we asked how this frequency-based habitization related to value-based operationalizations of habit and self-reported propensities for habitual behavior in real life. We find that choice frequency during training increases habit strength at test and that this form of habit shows little relation to value-based operationalizations of habit. Our findings empirically ground a novel perspective on the constituents of habits and suggest that habits may arise in the absence of external reinforcement. We further find no evidence for an overlap between different experimental approaches to measuring habits and no associations with self-reported real-life habits. Thus, our findings call for a rigorous reassessment of our understanding and measurement of human habitual behavior in the lab.

Making and breaking habits: Revisiting the definitions and behavioral factors that influence habits in animals

Habits have garnered significant interest in studies of associative learning and maladaptive behavior. However, habit research has faced scrutiny and challenges related to the definitions and methods. Differences in the conceptualizations of habits between animal and human studies create difficulties for translational research. Here, we review the definitions and commonly used methods for studying habits in animals and humans and discuss potential alternative ways to assess habits, such as automaticity. To better understand habits, we then focus on the behavioral factors that have been shown to make or break habits in animals, as well as potential mechanisms underlying the influence of these factors. We discuss the evidence that habitual and goal-directed systems learn in parallel and that they seem to interact in competitive and cooperative manners. Finally, we draw parallels between habitual responding and compulsive drug seeking in animals to delineate the similarities and differences in these behaviors.

Sex and individual differences in the effect of chronic low-dose ethanol on behavioral strategy selection

BACKGROUND

The development of an alcohol use disorder (AUD) involves impaired behavioral control and flexibility. Behavioral inflexibility includes an inability to shift behavior in response to changes in behavioral outcomes. Low levels of ethanol drinking may promote the formation of inflexible, habitual reward seeking, but this may depend on the timing of ethanol exposure in relation to learning. The goal of this study was to determine whether a history of low-dose ethanol exposure promoted contingency-insensitive sucrose seeking and altered behavioral strategy selection.

METHODS

Male and female C57BL/6J mice were trained to perform a response (lever press) for sucrose on two different reinforcement schedules: one that is thought to promote inflexible responding (random interval) and one that maintains flexible responding (variable ratio [VR]). Following instrumental training each day, mice were exposed to saline or low-dose ethanol (0.5 g/kg; i.p.) either proximal (1 h after) or distal (4 h after) to learning. Mice were then tested for sensitivity to changes in contingency in a contingency degradation test.

RESULTS

A history of low-dose ethanol exposure shifted behavioral strategy selection, as measured by reward tracking behavior, but this depended on sex and reinforcement schedule history. Both male and female mice used different strategies depending on the reinforcement schedule, but only males exhibited ethanol-induced shifts in strategy selection. A history of low-dose ethanol exposure did not impact contingency sensitivity in males but promoted insensitivity in females specifically on the VR lever.

CONCLUSIONS

Female mice show distinct behavioral effects of repeated, low-dose ethanol exposure as compared to males, with sex differences in the use of reward tracking strategies to guide behavior. Future studies should investigate sex differences in the neural consequences of chronic low-dose ethanol exposure that may underlie behavioral changes.

A dual-pathway architecture enables chronic stress to promote habit formation

Chronic stress can change how we learn and, thus, how we make decisions by promoting the formation of inflexible, potentially maladaptive, habits. Here we investigated the neuronal circuit mechanisms that enable this. Using a multifaceted approach in male and female mice, we reveal a dual pathway, amygdala-striatal, neuronal circuit architecture by which a recent history of chronic stress shapes learning to disrupt flexible goal-directed behavior in favor of inflexible habits. Chronic stress inhibits activity of basolateral amygdala projections to the dorsomedial striatum to impede the action-outcome learning that supports flexible, goal-directed decisions. Stress also increases activity in direct central amygdala projections to the dorsomedial striatum to promote the formation of rigid, inflexible habits. Thus, stress exerts opposing effects on two amygdala-striatal pathways to promote premature habit formation. These data provide neuronal circuit insights into how chronic stress shapes learning and decision making, and help understand how stress can lead to the disrupted decision making and pathological habits that characterize substance use disorders and other psychiatric conditions.

Food Restriction Level and Reinforcement Schedule Differentially Influence Behavior during Acquisition and Devaluation Procedures in Mice

Behavioral strategies are often classified based on whether reinforcer value controls reinforcement. Value-sensitive behaviors, in which animals update their actions when reinforcer value is changed, are classified as goal-directed; conversely, value-insensitive actions, where behavior remains consistent when the reinforcer is removed or devalued, are considered habitual. Basic reinforcement schedules can help to bias behavior toward either process: random ratio (RR) schedules are thought to promote the formation of goal-directed behaviors while random intervals (RIs) promote habitual control. However, how the schedule-specific features of these tasks interact with other factors that influence learning to control behavior has not been well characterized. Using male and female mice, we asked how distinct food restriction levels, a strategy often used to increase task engagement, interact with RR and RI schedules to control performance during task acquisition and devaluation procedures. We determined that food restriction level has a stronger effect on the behavior of mice following RR schedules compared with RI schedules, and that it promotes a decrease in response rate during devaluation procedures that is best explained by the effects of extinction rather than devaluation. Surprisingly, food restriction accelerated the decrease in response rates observed following devaluation across sequential extinction sessions, but not within a single session. Our results support the idea that the relationships between schedules and behavioral control strategies are not clear-cut and suggest that an animal's engagement in a task must be accounted for, together with the structure of reinforcement schedules, to appropriately interpret the cognitive underpinnings of behavior.

Effects of predictive and incentive value manipulation on sign- and goal-tracking behavior

When a neutral stimulus is repeatedly paired with an appetitive reward, two different types of conditioned approach responses may develop: a sign-tracking response directed toward the neutral cue, or a goal-tracking response directed toward the location of impending reward delivery. Sign-tracking responses have been postulated to result from attribution of incentive value to conditioned cues, while goal-tracking reflects the assignment of only predictive value to the cue. We therefore hypothesized that sign-tracking rats would be more sensitive to manipulations of incentive value, while goal-tracking rats would be more responsive to changes in the predictive value of the cue. We tested sign- and goal-tracking before and after devaluation of a food reward using lithium chloride, and tested whether either response could be learned under negative contingency conditions that precluded any serendipitous reinforcement of the behavior that might support instrumental learning. We also tested the effects of blocking the predictive value of a cue using simultaneous presentation of a pre-conditioned cue. We found that sign-tracking was sensitive to outcome devaluation, while goal-tracking was not. We also confirmed that both responses are Pavlovian because they can be learned under negative contingency conditions. Goal-tracking was almost completely blocked by a pre-conditioned cue, while sign-tracking was much less sensitive to such interference. These results indicate that sign- and goal-tracking may follow different rules of reinforcement learning and suggest a need to revise current models of associative learning to account for these differences.

Sensitivity to outcome devaluation in operant tasks is better predicted by food restriction level than reinforcement training schedule in mice

Behavioral strategies are often classified based on whether reinforcement is controlled by the value of the reinforcer. Value-sensitive behaviors, in which animals update their actions when reinforcer value is changed, are classified as goal-directed; conversely, value-insensitive actions, where behavior remains consistent when the reinforcer is removed or devalued, are considered habitual. Understanding the features of operant training that bias behavioral control toward either strategy is essential to understanding the cognitive and neuronal processes on which they rely. Using basic reinforcement principles, behavior can be biased toward relying on either process: random ratio (RR) schedules are thought to promote the formation of goal-directed behaviors while random intervals (RI) promote habitual control. However, how the schedule-specific features of these task structures relate to external factors to influence behavior is not well understood. Using male and female mice on distinct food restriction levels, we trained each group on RR schedules with responses-per-reinforcer rates matched to their RI counterparts to control for differences in reinforcement rate. We determined that food restriction level has a stronger effect on the behavior of mice following RR schedules than mice following RI schedules and that food restriction better predicted sensitivity to outcome devaluation than training schedule. Our results support the idea the relationships between RR or RI schedules with goal-directed or habitual behaviors, respectively, are more nuanced than previously appreciated and suggest that an animal's engagement in a task must be accounted for, together with the structure of reinforcement schedules, to appropriately interpret the cognitive underpinnings of behavior.

Task parameters influence operant response variability in mice

RATIONALE

During operant conditioning, animals associate actions with outcomes. However, patterns and rates of operant responding change over learning, which makes it difficult to distinguish changes in learning from general changes in performance or movement. Thus, understanding how task parameters influence movement execution is essential.

OBJECTIVES

To understand how specific operant task parameters influenced the repetition of future operant responses, we investigated the ability of operant conditioning schedules and contingencies to promote reproducible bouts of five lever presses in mice.

METHODS

Mice were trained on one of the four operant tasks to test three distinct hypotheses: (1) whether a cue presented concurrently with sucrose delivery influenced the pattern of lever pressing; (2) whether requiring animals to collect earned sucrose promoted the organization of responses into bouts; and (3) whether only reinforcing bouts where interresponse time (IRT) variances were below a target promoted reproducible patterns of operant behavior.

RESULTS

(1) Signaling reinforcer delivery with a cue increased learning rates but resulted in mice pressing the lever in fast succession until the cue turned on, rather than executing discrete bouts. (2) Requiring mice to collect the reinforcer between bouts had little effect on behavior. (3) A training strategy that directly reinforced bouts with low variance IRTs was not more effective than a traditional fixed ratio schedule at promoting reproducible action execution.

CONCLUSIONS

Together, our findings provide insights into the parameters of behavioral training that promote reproducible actions and that should be carefully selected when designing operant conditioning experiments.