Opponent Learning with Different Representations in the Cortico-Basal Ganglia Pathways Can Develop Obsession-Compulsion Cycle

Obsessive-compulsive disorder (OCD) has been suggested to be associated with impairment of model-based behavioral control. Meanwhile, recent work suggested shorter memory trace for negative than positive prediction errors (PEs) in OCD. Relation between these two suggestions remains unclear. Based on the properties of cortico-basal ganglia pathways, we modeled human as agent having a combination of successor representation (SR)-based system that enables model-based-like control and individual representation (IR)-based system that only hosts model-free control. We show that if the SR- and IR-based systems learn mainly from positive and negative PEs, respectively, agent can develop obsession-compulsion cycle, similarly to the agent with memory trace imbalance in the previous study. Fitting of behavior of such an opponent SR+IR agent in the two-stage decision task resulted in smaller weights for model-based control than the SR-only agent. These results reconcile the previous suggestions about OCD, raising a possibility that opponent learning in model-based/free controls underlies obsession-compulsion. Moreover, together with a recent suggestion that the opponent SR+IR combination actually performs well in certain dynamic environments and its cortico-striatal implementation appears consistent with various findings, this possibility explains why human is prone to OCD and even healthy people tended to show shorter memory trace for negative PEs.