Disruption of prefrontal cortex accelerates sensory anchoring but dissociates online recognition from implicit consolidation of sound sequences

Abstract

The auditory brain excels at extracting predictive regularities from sound, but the neural and temporal mechanisms mediating long-term learning of these regularities remain poorly understood. Here, using a perceptual anchoring paradigm, we investigate whether the dorsolateral prefrontal cortex (dlPFC) is causally required to transform transient regularities into stable internal templates (anchors). We characterized the behavioural dynamics of anchoring to predicable acoustic events using sensitivity (d) and decision bias (c) metrics, alongside growth curve analysis (GCA) to model trial-by-trial learning. Listeners exhibited a robust anchoring effect, showing significantly higher sensitivity in decision strategy for recurring acoustic regularities compared to novel ones. This implicit anchoring was driven selectively by specific features in regular sequences--the local repetition of an acoustic motif--whereas explicit memory indiscriminately encoded the entire acoustic episode. To test for causality, we applied inhibitory continuous theta-burst stimulation (cTBS) to the dlPFC. Crucially, not only did this not impair anchoring, but significantly accelerated the rate of anchoring for predictable patterns, suggesting the dlPFC may act as a source of top-down interference in implicit learning. In contrast to predictable sequences, inhibition of dlPFC disrupted the initial precision of online comparisons for novel sequences, though insulating against the rapid, interference-driven reduction in performance or novel sequences in observed in listeners subjected to a sham cTBS procedure. These findings reveal a functional dissociation. Whilst dlPFC provides an essential buffer for novel sensory comparisons, long-term consolidation of regularities in acoustic sequences relies on a robust implicit pathway independent of prefrontal control.