Learning from the Unexpected: How Prediction Errors Shape Episodic Memory Formation

Abstract

Updating memory in response to unexpected outcomes is critical for maintaining an adaptive internal model of the world. While prediction errors (PEs) have long been central to theories of reinforcement learning, emerging evidence indicates they also play a key role in shaping episodic memory, although their underlying mechanisms remain poorly understood. This thesis systematically investigates how PEs, particularly in aversive contexts, influence episodic memory formation by uncovering their cognitive and neural underpinnings. Across five studies, we employed modified versions of an incidental encoding-fear learning task to examine how expectancy violations modulate memory. Studies I and II replicated previous findings that unsigned PEs retrospectively enhance memory for predictive stimuli, and further demonstrated that these effects also occur prospectively and independently of physiological arousal. Studies III to V extended these findings by revealing that signed PEs affect memory formation in a direction-specific manner, with positive PEs enhancing and negative PEs attenuating memory. Study III investigated the temporal constraints of PE-induced memory enhancements by varying the delay between predictive cues and outcomes. Results showed that temporal proximity is not essential for PE-driven memory enhancements, suggesting that contingency, rather than contiguity, plays a critical role. Study IV examined the specificity of PE effects by testing whether memory enhancements also occur for uninformative, i.e., unpredictive, stimuli encountered near the PE event. The memory benefits were restricted to predictive cues, supporting a selective encoding mechanism susceptible to interference. Finally, Study V combined EEG with inhibitory continuous theta burst stimulation (cTBS) over the right superior parietal cortex (rSPC) to explore its causal role in PE-induced memory modulations and the neural dynamics surrounding PEs. Alpha and theta oscillations before the PE and stimulus reactivation after the PE predicted enhanced memory, depending on the direction of the PE. Interestingly, inhibiting the rSPC paradoxically boosted memory, suggesting that reduced top-down filtering may facilitate memory formation under surprise. Together, these findings suggest that PEs promote the selective encoding and consolidation of behaviorally relevant events into long-term memory by engaging attention, working memory, and salience networks. These insights provide translational potential for clinical interventions by identifying mechanisms through which maladaptive processes in fear-related disorders could be altered.