Hearing Impairment Is Associated with Smaller Brain Volume in Aging

Abstract

Although recent studies show that age-related hearing impairment is associated with cerebral changes, data from a population perspective are still lacking. Therefore, we studied the relation between hearing impairment and brain volume in a large elderly cohort. From the population-based Rotterdam Study, 2,908 participants (mean age 65 years, 56% female) underwent a pure-tone audiogram to quantify hearing impairment. By performing MR imaging of the brain we quantified global and regional brain tissue volumes (total brain volume, gray matter volume, white matter (WM) volume, and lobe-specific volumes). We used multiple linear regression models, adjusting for age, sex, head size, time between hearing test and MR imaging, and relevant cognitive and cardiovascular covariates. Furthermore, we performed voxel-based morphometry to explore sub-regional differences. We found that a higher pure-tone threshold was associated with a smaller total brain volume [difference in standardized brain volume per decibel increase in hearing threshold in the age-sex adjusted model: -0.003 (95% confidence interval -0.004; -0.001)]. Specifically, WM volume was associated. Both associations were more pronounced in the lower frequencies. All associations were consistently present in all brain lobes in the lower frequencies and in most lobes in the higher frequencies, and were independent of cognitive function and cardiovascular risk factors. In voxel-based analyses we found associations of hearing impairment with smaller white volumes and some smaller and larger gray volumes, yet these were statistically non-significant. Our findings demonstrate that hearing impairment in elderly is related to smaller total brain volume, independent of cognition and cardiovascular risk factors. This mainly seems to be driven by smaller WM volume, throughout the brain.

Keywords: age-related hearing impairment; brain MRI; pure-tone audiogram; voxel-based analysis; white matter.

FIGURE 1

The template image for the individual lobes as seen from three axial coupes. Blue–gray = right frontal lobe; Red = left frontal lobe; Brown = right parietal lobe; Purple = left parietal lobe; Green = right occipital lobe; Yellow = left occipital lobe; Blue = right temporal lobe; Turquois = left temporal lobe.

FIGURE 2

Association for hearing thresholds and white matter (WM) volume displayed for the different lobes. First: Variation for low frequency pure-tone threshold. Second: Variation for high frequency pure-tone threshold. Boxplots show the difference in SD WM volume per decibel hearing threshold. Significant findings (α < 0.05) are marked with ^∗. This model was adjusted for age, age², sex, time between MRI and audio, intracranial volume, educational level, MMSE score, systolic and diastolic heart rate, BMI, DM, cholesterol ratio, smoking and alcohol consumption. L, Left; R, Right; SD, Standard deviation.

FIGURE 3

Projection of voxel based WM areas on axial coupes associated with age-related hearing impairment. Colors reflect the tendency of the association: blue for a negative direction (decrease of WM), red for a positive direction (increase of WM). See Supplementary Tables for exact outcome per area.

FIGURE 4

Projection of voxel based gray matter areas on axial coupes associated with age-related hearing impairment. Colors reflect the tendency of the association: blue for a negative direction (decrease of gray matter), red for a positive direction (increase of gray matter). See Supplementary Tables for exact outcomes per area.