Abstract
Recent evidence suggests that reward prediction errors (RPEs) play an important role in declarative learning, but its neurophysiological mechanism remains unclear. Here, we tested the hypothesis that RPEs modulate declarative learning via theta-frequency oscillations, which have been related to memory encoding in prior work. For that purpose, we examined the interaction between RPE and transcranial Alternating Current Stimulation (tACS) in declarative learning. Using a between-subject (real versus sham stimulation group), single-blind stimulation design, 76 participants learned 60 Dutch-Swahili word pairs, while theta-frequency (6 Hz) tACS was administered over the medial frontal cortex (MFC). Previous studies have implicated MFC in memory encoding. We replicated our previous finding of signed RPEs (SRPEs) boosting declarative learning; with larger and more positive RPEs enhancing memory performance. However, tACS failed to modulate the SRPE effect in declarative learning and did not affect memory performance. Bayesian statistics supported evidence for an absence of effect. Our study confirms a role of RPE in declarative learning, but also calls for standardized procedures in transcranial electrical stimulation.
Highlights
Declarative memory consists of memory for facts and events that can be consciously recalled [1, 2]
This study revealed that reward prediction errors (RPEs) responses in the ventral striatum (VS) at reward feedback predicted memory performance
We verified whether recognition accuracy linearly increased with signed RPEs (SRPEs)
Summary
Declarative memory consists of memory for facts and events that can be consciously recalled [1, 2]. The process of acquiring such memories is called declarative learning. Declarative memory differs from procedural memory, where a skill is learned slowly and by means of repeated practice (e.g., learning how to drive a car). Research has firmly established that prediction errors modulate declarative memory [4], just like they do in procedural memory [5]. Recent research shows that reward prediction errors (RPE; i.e., mismatches between reward outcome and reward prediction) may facilitate memory formation. RPEs were primarily studied within procedural learning (e.g., [6]). Recent evidence suggests that RPEs are crucial for declarative learning as well [7,8,9]
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