Alterations of brain activity in noise-exposed rats after transcutaneous auricular vagus nerve stimulation evaluated via fMRI

Abstract

This study aims to explore the role of the central nervous system network outside the auditory system in the development process of noise − induced central injury. A noise-exposed rat model was established with unilateral narrow-band noise. Auditory brainstem response (ABR) measured hearing thresholds at Click and 8, 16, 24, 32 kHz pre- and post-noise exposure. Experimental rats were split into transcutaneous auricular vagus nerve stimulation (ta-VNS) and sham subgroups for 2-week intervention. Resting-state fMRI (rs-fMRI) was performed on all groups (ta-VNS, sham, control) post-noise exposure and 2 weeks post-intervention. After noise exposure, 22 rats had elevated hearing thresholds at 8, 24, 32 kHz. fMRI revealed increased ALFF/ReHo in the entorhinal cortex, amygdalar cortex, and hippocampus, decreased values in the prelimbic cortex, basal forebrain, striatum, and cingulate cortex, and enhanced cingulate cortex-basal forebrain functional connectivity. The rats were divided into ta-VNS (n = 10) and sham (n = 12) subgroups for 2-week intervention. Compared with the control group (n = 9), both subgroups showed similar brain activation/inhibition in regions like the entorhinal cortex pre- vs. post-intervention. However, the ta-VNS group reversed noise-induced reduced neural activity in the prelimbic cortex and basal forebrain, and significantly enhanced their functional connectivity. Noise exposure increased entorhinal cortex, hippocampus, and amygdala activity in rats, potentially linked to aversive emotions and abnormal auditory memory. The prelimbic cortex-centered network may gate noise-induced aversive perception, with cingulate cortex activity/connectivity disrupted. ta-VNS may alleviate such perception by reversing reduced neural activity in gating-related regions and enhancing their connectivity, plus strengthening brainstem-limbic and brainstem-cerebellum functional links.