Habit formation viewed as structural change in the behavioral network

Habit formation is a process in which an action becomes involuntary. While goal-directed behavior is driven by its consequences, habits are elicited by a situation rather than its consequences. Existing theories have proposed that actions are controlled by corresponding two distinct systems. Although canonical theories based on such distinctions are starting to be challenged, a few theoretical frameworks that implement goal-directed behavior and habits within a single system. Here, we propose a novel theoretical framework by hypothesizing that behavior is a network composed of several responses. With this framework, we have shown that the transition of goal-directed actions to habits is caused by a change in a single network structure. Furthermore, we confirmed that the proposed network model behaves in a manner consistent with the existing experimental results reported in animal behavioral studies. Our results revealed that habit could be formed under the control of a single system rather than two distinct systems. By capturing the behavior as a single network change, this framework provides a new perspective on studying the structure of the behavior for experimental and theoretical research. Author summaryTo obtain the desired consequences, organisms need to respond based on the knowledge of the consequences obtained by the response and the change in the environment caused by it. Such a process is called goal-directed behavior, which is flexible, but requires high computational cost. Once the same response is repeatedly performed under the same environment, the response becomes automatic, and transforms into a habit. In the canonical views, such a change from goal-directed response to habit was explained by the associative structures between the corresponding systems, goal-directed, and habit systems. However, the dichotomy in the mechanisms of behavior between goal-directed responses and habits has recently been challenged. Here, we show that, instead of assuming two explicitly distinguished mechanisms as in the canonical views, behavior is regarded as a network consisting of multiple responses, and that changes in the structure of the network cause two behavioral features, goal-directed behavior and habit. The transition from goal-directed behavior to habit has been operationally defined by sensitivity to the reward obtained by the response. We replicate such an experimental paradigm in the simulation and show that the behavioral network model can reproduce the empirical results on habit formation obtained from animal experiments. Our results demonstrate that habit formation can be explained in terms of changes in the network structure of behavior without assuming explicitly distinct systems and thus, provide a new theoretical framework to study the psychological, biological, and computational mechanisms of the behavior.