Causal Modulation of Brain Body Habituation Dynamics Implicates Salience Network Mechanisms in Anxiety

Anxiety is marked by exaggerated vigilance which may be linked to impaired sensory habituation, yet the physiological mechanisms linking anxiety to dysregulated habituation in the brain remain unclear. The brains ability to filter sensory input is characteristic of healthy functioning and disruption of this can lead to over-responsiveness and hypervigilance that may underlie pathological anxiety. Here, we examined how state and trait anxiety relate to acoustic startle reflex habituation across somatic (EMG), cortical (EEG), and autonomic (electrodermal; EDR) responses, and whether casual modulation of the right anterior insula (AI) or anterior mid-cingulate cortex (aMCC) using low-intensity focused ultrasound (LIFU) modulates these dynamics. As part of a larger study, forty participants (median STAI-T = 39.5; range 25 - 68) completed three LIFU sessions (AI, aMCC, Sham) while EMG, EEG, and EDR were recorded during 12 acoustic startle stimuli both before and after LIFU. Habituation slopes were computed separately for early (Trials 2-6) and late (Trials 7-12) windows using Theil-Sen estimators and analyzed with linear mixed-effects models controlling for baseline magnitude (Trial 1) and anxiety covariates. Before LIFU, higher trait anxiety predicted weaker EMG habituation ({rho} {approx} 0.3), whereas state anxiety showed no reliable association with any modality. Across sessions, early slopes were steeper than late slopes for all measures, indicating reduced adaptation with repetition. LIFU to AI or aMCC did not alter EMG or EEG habituation but significantly enhanced early-phase EDR habituation relative to sham, suggesting transient facilitation of autonomic adaptation. Cross-modal analyses revealed robust coupling between EMG and EEG habituation ({rho} {approx} 0.4-0.5, p < 0.01), independent of anxiety, whereas EDR habituation varied independently. Mean response magnitudes of EMG, EEG or EDR across trials were unrelated to anxiety and were not affected by LIFU. These findings identify coordinated cortical-somatic habituation as an anxiety-relevant biomarker and demonstrate that the AI and aMCC are involved in autonomic adaptation to sensory stimuli. Neuromodulation of these regions may provide potential therapeutic benefit to reduce autonomic reactivity to anxiety provoking stimuli.