Prefrontal and Cerebellar Contributions to Semantic Memory Retrieval.

Semantic memory retrieval is essential for language, thought, and adaptive behavior. Although both the prefrontal cortex (PFC) and the cerebellum have been implicated in this function, the role of the PFC remains poorly understood and the contribution of the cerebellum largely overlooked in current neurocognitive models. To address these gaps, we conducted a double-blind, randomized, placebo-controlled experiment in which healthy adults received anodal transcranial direct current stimulation (tDCS) targeting the left lateral PFC, the right posterior cerebellum, or sham stimulation. Participants completed a novel process-sensitive paradigm comprising lexical decision, free-associative (FA; automatic) retrieval, dissociative (DA; controlled) retrieval, and intrusion monitoring, while manipulating response predictability and rule switching. Cerebellar tDCS selectively impaired FA performance, particularly for cues evoking predictable responses, supporting its role in automatic access to overlearned associations. In contrast, prefrontal tDCS disrupted DA performance and increased associative intrusions, implicating the PFC in retrieval inhibition. Importantly, mediation analysis showed that the reduction in DA fluency was largely explained by higher probability of intrusions, indicating a perturbation of proactive inhibitory control that normally prevents irrelevant memory activations from entering working memory. Further exploratory analyses ruled out several alternative accounts of these stimulation effects, underscoring their process specificity. Together, these findings advance models of semantic cognition by demonstrating complementary contributions of the cerebellum to automatic retrieval and of the PFC to inhibitory control over intrusions.