Auditory selective attention impairments in blast-exposed veterans with traumatic brain injury

Abstract

A common complaint among returning combat veterans who have experienced some form of blast-related traumatic brain injury (bTBI) is difficulty understanding speech in noisy environments. Given that many veterans have noise-induced hearing deficits, hearing loss is one factor that may contribute to such complaints. Specifically, sensorineural hearing loss likely interacts with damage to cortical structures important for controlling selective attention, leading to severe difficulties when trying to communicate in everyday social settings. We evaluated 10 bTBI veterans' hearing status as well as their performance on a selective auditory attention task. In the veterans tested, audiograms revealed near-normal auditory thresholds (within 20 dB of normal limits). In addition, a more sensitive test of supra- threshold temporal coding fidelity in the brainstem recently developed in our laboratory revealed responses within the normal range for healthy young adults. Thus, in this pilot study, there was no evidence for sensorineural hearing deficits, even using new methods for revealing differences in supra-threshold hearing. The bTBI veterans performed a selective auditory attention task in which they were instructed to categorize the pitch contour of one of three simultaneously occurring melodies presented from three differently perceived locations (either rising, falling, or alternating).Such a task not only requires fine attentional control, but also temporally precise neural representations of the incoming sensory information. Performance was significantly worse compared to 17 normal-hearing , non-TBI controls. EEG recorded evoked response potentials to correctly identified trials showed that in those veterans who could perform the task at above chance levels, attention modulated the neural representation of the auditory input weakly or not at all, whereas healthy controls consistently show such modulation. Although these results do not rule out auditory sensory deficits as a contributing factor to selective auditory attention deficits in the general population of bTBI veterans, they suggest that blast exposure damage affects cortical regions responsible for controlling selective auditory attention. These findings are a step toward developing early pre-clinical diagnostic markers for long-term neurobehavioral disorders commonly associated with bTBI.