Recovery of Function Following Exposure to Intense Sound 
    Excessive and dangerous sound levels capable of producing permanent hearing loss abound in our society.  They are more associated with our recreational activities than with the work place where OSHA regulations have set standards that limit the exposure to damaging sound levels. 
    A number of investigations are directed toward understanding the underlying mechanisms of acoustic injury to the ear and the processes that govern the recovery from acoustic trauma.  Young chicks serve as an animal model because of the remarkable ability of this species to regenerate new hair cells in replacement of those lost to the loud sound exposure.  Physiologic responses of the inner ear and cochlear nerve are used to trace the process of functional recovery.  The inner ear endocochlear potential is studied by using ion selective electrodes to measure post-exposure ionic changes in scala media.  Single-nerve fibers of the cochlear nerve are characterized by their response to sound following exposure.  Currently we are examining the coding of rate-intensity functions and phase-locking in the responses of these nerves.  In addition, distortion product otoacoustic emissions are being measured to determine if there are gross mechanical changes in the chick sound-damaged cochlea.  These emissions are studied using the cubic difference tone, which is reflected out of the inner ear and measured as an acoustic signal in the ear canal.  Changes in the central nervous system as a consequence of acoustic injury in the cochlea are also being examined.  Cells in the brainstem nucleus magnocellularis are studied both morphologically, physiologically and biochemically to determine their response to altered input following cochlear damage. 
    Finally, we routinely use scanning electron microscopy to examine the details of injury to the surface of the cochlea, and to quantitatively trace structural changes as the chick inner ear recovers.