Structural Alterations in a Rat Model of Short-Term Conductive Hearing Loss Are Associated With Reduced Resting State Functional Connectivity

Abstract

Conductive hearing loss (CHL) results in attenuation of air conducted sound reaching the inner ear. How a change in air conducted sound alters the auditory system resulting in cortical alterations is not well understood. Here, we have assessed structural and functional magnetic resonance imaging (MRI) in an adult (P60) rat model of short-term conductive hearing loss (1 week). Diffusion tensor imaging (DTI) revealed fractional anisotropy (FA) and axial diffusivity alterations after hearing loss that circumscribed the auditory cortex (AC). Tractography found the lateral lemniscus tract leading to the bilateral inferior colliculus (IC) was reduced. For baseline comparison, DTI and tractography alterations were not found for the somatosensory cortex. To determine functional connectivity changes due to hearing loss, seed-based analysis (SBA) and independent component analysis (ICA) were performed. Short term conductive hearing loss altered functional connectivity in the AC and IC, but not the somatosensory cortex. The results present an exploratory neuroimaging assessment of structural alterations coupled to a change in functional connectivity after conductive hearing loss. The results and implications for humans consist of structural-functional brain alterations following short term hearing loss in adults.

Auditory–limbic–cerebellum interactions and cognitive impairments in noise‐induced hearing loss

“…Significant structural changes were found in the IC and medial geniculate body, but not the ACx. Another rat model of conductive hearing loss only found the reduced lateral lemniscus (LL) fiber tract in the duration of 1 week 11 . These inconsistencies with our findings are probably due to the progression of hearing loss since our research followed up for 6 months and tracked the process of brain remodeling underlying NIHL.…”

“…Firstly, we did not find any correlations between MRI and behavioral tests, which may be due to the limited sample size. And we applied uncorrected p‐ value in imaging analysis, as it is reported that a small sample size might contribute to a low signal‐to‐noise ratio and poor statistical power 11 . Future studies should expand it and address data quality.…”

“…Functional connections are defined as the temporal coincidence of neurophysiological events (including anatomical structure and functional associations) and effectively describe information flow between brain areas 10 . Additionally, diffusion tensor imaging (DTI) can reveal microstructural changes in white matter and has been widely used in animal models 11 …”

“…10 Additionally, diffusion tensor imaging (DTI) can reveal microstructural changes in white matter and has been widely used in animal models. 11 In the present study, we used a broadband noise exposure for 2 h (122 dB SPL) to establish noise-induced hearing loss (NIHL) model.…”

Structural and Functional Hippocampal Correlations in Environmental Enrichment During the Adolescent to Adulthood Transition in Mice

“…Continuous physiological monitoring was performed using an MRI-compatible system (SA Instruments, Stony Brook, NY, United States). Vital signs were within normal physiological ranges (rectal temperature, 36.5–37.5°C; heart rate, 350–420 beats/min; breathing, > 80–100 breaths/min; oxygen saturation, ∼95% with a pulse oximeter) throughout the experiment ( Chan et al, 2009 ; Lau et al, 2011 ; Cheung et al, 2012a , b ; Zhou et al, 2014 ; Manno et al, 2019 , 2021 ). After the mouse was placed in the scanner, scout images were acquired along the axial, coronal, and sagittal views to position MRI slices accurately.…”