Controlled cortical impact-induced brain injury alters auditory sensitivity in laboratory mice

Individuals who have sustained a traumatic brain injury (TBI) often report auditory dysfunction including changes to their hearing sensitivity, tinnitus, and hyperacusis. One factor that may have a significant contribution to a person’s post-injury outcomes is whether the TBI occurred in combination with a high intensity noise exposure (e.g., as in the case of a car accident). To date, no study has examined the combined effects of a brain injury and high intensity noise exposure to evaluate whether this would lead to worse overall auditory outcomes than either trauma in isolation. In this study we tested the auditory sensitivity of male and female CBA/CaJ laboratory mice before and 3, 7, 14, 30, 60, and 90 days after acoustic (noise exposure), physical (controlled cortical impact), and combined acoustic and physical injuries. Following completion of the experiment, cochlear and brain tissue was fixed with paraformaldehyde and central and peripheral auditory structures were examined for damage. Our preliminary results show that physical injuries alone cause damage to the auditory sensitivity of mice measured using the auditory brainstem response, reduced acoustic startle responses in quiet and noise, yet hair cells remain intact. Long-term consequences on auditory perception are being tracked in these mice.