The selective dynamics of proactive and reactive control in GAD: A taVNS study using hierarchical drift diffusion modeling.

Anxiety has been linked to mode-specific dysregulation in cognitive control, characterized by reduced proactive maintenance and heightened reliance on reactive engagement. Yet many neuromodulation studies implicitly assume a unitary enhancement of control. We tested whether acute transcutaneous auricular vagus nerve stimulation (taVNS) produces global or context-dependent changes in cognitive control. Thirty-one individuals with generalized anxiety disorder completed a within-subject, single-blind, counterbalanced study comparing active and sham taVNS across two sessions. Participants performed the AX Continuous Performance Task, which dissociates proactive and reactive control demands. Conventional behavioral indices, including reaction time, accuracy, d'-context, and proactive behavioral indices, did not show reliable stimulation-specific changes. Hierarchical drift diffusion modeling further suggested that stimulation-related effects were subtle and uncertain. A modest directional pattern emerged for boundary separation in AY trials, where active taVNS appeared to preserve decision caution relative to a sham-related decline; however, the 95% HDI included zero. Structural and RT-threshold sensitivity analyses retained the positive direction of this contrast but did not remove its uncertainty. These findings do not establish a robust enhancement of cognitive control, but provide limited preliminary evidence for possible context-dependent preservation of decision gating.