Over 1.5 million individuals in the United States sustain traumatic brain injury (TBI) each year, and over 5 million Americans of all ages are living with long-term disabilities resulting from TBI. Any brain injury - whether mild, moderate, or severe - can have devastating consequences on an individual's daily life. The auditory pathway is one of the brain systems highly vulnerable to damage as a result of TBI, and some of the problems these individuals experience may result from an inability to efficiently process auditory information. Recent evidence suggests that more than 50% of adult and pediatric patients with TBI have evidence of auditory processing problems (Bergemalm &Borg, 2001;Bergemalm &Lyxell, 2005;Flood et al., 2005). These processing problems may cause difficulty comprehending verbal instructions and a need for repeated instructions in school or at work, in addition to having social and emotional implications. Thus, it is critical to accurately diagnose the effect of TBI on the auditory system, specifically the central auditory pathway. The goal of the proposed study is to examine neural correlates of auditory processing in individuals with TBI using a novel approach of recording auditory evoked potentials (AEPs) from multiple levels of the central auditory system in response to speech stimuli. Participants for this project will include 40 individuals with mild TBI (20 mild and 20 moderate) and age-matched controls. Specifically, we will measure the magnitude and timing of the neural response to speech using brainstem, cortical, and cognitive AEPs, and compare these AEP outcomes to performance on behavioral tests of central auditory processing abilities. Our working hypotheses are 1) that individuals with TBI will have evidence of impaired neural processing at one or more levels in the auditory processing pathway, as demonstrated by abnormal neural patterns recorded in quiet and/or in noise, and 2) that these AEP outcomes will correlate with reduced performance on behavioral tests of auditory processing and cognitive skills. The proposed study is focused on TBI, which is a major public health concern in the United States;however, the findings will also have implications for individuals with a wide range of developmental and acquired disorders of the central auditory system. The proposed research is clinically significant because the outcomes will contribute to our understanding of appropriate measures for determining central auditory dysfunction and further our knowledge of how complex signals are processed in individuals with TBI and other central auditory disorders.
The public health relevance of this research is to improve diagnosis of auditory-based communication disabilities and general neurophysiologic dysfunction for the estimated over 1.5 million Americans who sustain traumatic brain injury each year. We will use a novel objective approach to evaluate the effect of injury on the representation and processing of speech sounds at multiple levels within the central auditory nervous system.