Functional hearing difficulties in Veterans with blast and blunt head trauma are associated with reduced fractional anisotropy in putative auditory radiations.

Objectives: Veterans of recent military conflicts have experienced a high rate of mild traumatic brain injury (mTBI) due to blast exposure. A debilitating symptom often reported by such patients is an impaired ability to perceive complex sounds (e.g., impaired speech comprehension in noisy environments). In a prior report, we found a continuous measure of historical mTBI to be associated with changes in diffusion tensor imaging (DTI) metrics across a large number of cortical white matter tracts among young to middle-aged Veterans. Notable among these tracts were the auditory radiations (AR), which connect subcortical and cortical auditory centers. Here, we further hypothesize that the changes to the AR correlate with a loss of auditory perceptual ability.

Design: In the present study, we analyze the same DTI data using a novel application of Randomized Parcellation Based Inference (RPBI), to identify regions in which white matter integrity (reduced fractional anisotropy) is correlated with both the mTBI index used previously, and with an objective measure of functional hearing difficulty (clinical words-in-noise test scores).

Results: In a whole-brain analysis performed on the white matter skeleton, increased functional hearing difficulty and higher levels of blast and blunt head traumas were associated with reduced fractional anisotropy in circumscribed regions at the stems of the left and right temporal lobes (sagittal stratum). Comparison of these voxels to the AR, as delineated using probabilistic tractography in the same sample and a probabilistic atlas based on histological staining (Juelich), showed strong overlap between the whole-brain effects and the putative AR.