Continuous Strategy Adaptation and Discrete Switching Driven by Environment and Internal State in Meta-Learning

AO_SCPLOWBSTRACTC_SCPLOWBehavioral strategies can change in response to environmental and internal states, either gradually or abruptly, enabling flexible adaptation. Such strategy regulation is central to meta-learning, the ability to learn to learn. Previous studies analyzed temporal or condition-dependent strategy change using models and theories that assume continuous or discrete changes. Here, we analyze the mices behavior in a two-step decision task using four different approaches: stay-switch choice probability analysis; generalized linear mixed model (GLMM) of choice and reaction time (RT) given preceding task events; fitting a reinforcement learning (RL) model with time-varying meta-parameter by a novel multiple-step particle filtering method; and fitting a finite internal state (FIS) model that produces choice and RT depending on discrete state transition. Together, the stay probability and GLMM analyses reveal that learning progress encourages a shift toward a model-based, value-based learning strategy, accompanied by elevated choice perseveration. More uncertain reward settings or changes in them lead to random, exploratory behavior. Meta-parameter dynamics show faster learning, greater involvement of a model-based strategy, higher choice stochasticity, and more rapid development of choice perseveration with less contribution to the final decision as learning progresses. Exploratory behavior in the face of uncertain reward settings or changes in those settings is underpinned by slower forgetting and greater model-based contribution. FIS modeling discovered a trial-level switch between an optimal value-based learning state and a suboptimal self-repeating state. Meta-parameter dynamics reflect continuous strategy changes, while state transitions capture abrupt, discrete strategy switches. At an intermediate timescale, when reward settings change, two processes interact: mice persist in a self-repeating state, leading to attempts at model-based strategy with incomplete adaptation.