No effect of partial reinforcement on fear extinction learning and memory in C57BL/6J mice

Abstract

Partial reinforcement schedules, wherein a conditioned stimulus (CS) is intermittently paired with an unconditioned stimulus (US) during associative learning, have been widely studied and found to affect the extinction and recall of learned behaviors. Notably, behaviors conditioned under partial (as opposed to consistent) reinforcement are more resistant to extinction, an effect known as the partial reinforcement extinction effect (PREE). The present study initially aimed to examine the effects of partial reinforcement on the acquisition and recall of fear extinction (FE) when altering the contextual environment. However, our systematic investigation of partial reinforcement using C57BL/6J mice challenges the well-established PREE within the domain of FE learning. Across multiple experimental setups altering CS duration, US intensity, and reinforcement schedules, we consistently found no significant impact of partial reinforcement on the acquisition, consolidation, or recall of FE. Mice exhibited similar patterns of extinction and spontaneous recovery of conditioned fear responses regardless of reinforcement schedule. These findings suggest that partial reinforcement during fear acquisition may not confer resistance to extinction of conditioned freezing, challenging the established understanding of the PREE and prompting a reexamination of how reinforcement schedules affect learning and memory of fear-related behaviors.