Neural, vascular, motor and autonomic habituation to high-intensity auditory stimulation: A multimodal characterization of the human defensive responses.

Abstract

The defense reflex has been extensively characterized across sensory modalities; however, the integration of electrical, neurovascular, motor, and peripheral autonomic responses involving the central and autonomic nervous systems remains poorly understood. This study investigated defensive responses to high-intensity auditory stimulation using a multimodal approach combining electroencephalography (EEG), functional near-infrared spectroscopy (fNIRS), and peripheral physiological measures. Participants were exposed to twenty white-noise bursts (100 dB, 500 ms, instantaneous rise time) separated by silent intervals (50 ± 10 s), grouped into five blocks to assess initial responses and habituation. Hemodynamic responses revealed widespread activation of bilateral auditory and frontal regions following stimulus onset, with a progressive reduction in response amplitude and extension of active channels across blocks. Network analysis suggests progressive reorganization of functional connectivity between sensory and frontal regions across repeated stimulation. At the peripheral level, habituation was observed in phasic electrodermal activity, vascular indices, motor response, EEG-derived ocular activity, and parasympathetic cardiac modulation, primarily after the first block, whereas respiratory measures remained stable. Cardiac defense-like responses show a multi-temporal component structure, with habituation restricted to the late decelerative phase. Multivariate analyses revealed a structured yet partially independent organization of neural and autonomic responses to habituation. Together, these findings provide a comprehensive characterization of multisystem responses to intense auditory stimulation, highlighting selective habituation across central, neurovascular, motor, and autonomic systems, and offering new insights into how neurovascular and peripheral processes adapt to repeated auditory threats.