Auricular transcutaneous vagus nerve stimulation enhances stimulus-response binding effects - Evidence from drift diffusion modeling.

Auricular transcutaneous vagus nerve stimulation (atVNS) has been proposed to modulate cognitive control by sharpening gain processes via potential increase in norepinephrine (NE) and gamma-aminobutyric acid (GABA) levels. Yet, its impact on the core mechanisms of action control remains unclear. According to the Binding and Retrieval in Action Control (BRAC) framework, flexible behavior relies on integrating stimulus and response features into event-files and their subsequent retrieval. Here, we investigated whether atVNS alters stimulus-response (S-R) binding in a manner consistent with the proposed modulation of the signal-to-noise ratio of perceptual-motor representations. In a randomized single-blind design, healthy participants received active or sham atVNS while performing a standard binding task. Behavioral analyses revealed robust S-R binding effects across groups. Critically, the active atVNS group showed significantly larger S-R binding effects in reaction times than the sham group. To determine in which cognitive subprocesses this behavioral modulation was expressed, we applied drift diffusion modeling (DDM). Consistent with gain-control accounts, atVNS enhanced S-R binding effects in the drift rate, consistent with a modulation of evidence accumulation across task conditions. These findings provide the first DDM-based evidence that atVNS-related differences in integration and/or retrieval processes central to BRAC may be expressed in the accumulation of task-relevant evidence. Taken together, the results suggest that atVNS modulates S-R binding effects, potentially through changes in event-file integration and/or retrieval, thereby offering a theoretical link between neurochemical gain modulation and action control.