A Formal Theory of Mood Instability

Despite empirical progress, theoretical understanding of mood instability remains stagnant. A major reason for this stagnation concerns the field’s reliance on narrative theories that cannot integrate disparate quantitative perspectives on mood dynamics. Here, we address the limitations of narrative theorizing by developing a formal theory of mood instability. Our theory is predicated on the computational process of “evaluation”: the process of appraising the value of stimuli, which has long been theorized to be central to mood dynamics. Building on reinforcement-learning models of evaluation, we propose a dynamic framework, which we use to simulate various evaluative situations. Our simulations can generate and thereby formally integrate three well-known types of mood instability: emotional rigidity/inertia, transience/instability, and sensitivity/reactivity. We discuss how this formal perspective could enhance the theory, clinical utility, and measurement of mood instability.