Central auditory system neuroplasticity and hippocampal neurogenesis following cochlear insults

Sensorineural hearing loss from noise exposure and ototoxic drugs has traditionally been thought of as an exclusively cochlear phenomenon because of compelling evidence of damage to the hair cells and spiral ganglion neurons. However, there is growing evidence that cochlear pathology leads to a plethora of functional and subtle anatomical changes at multiple sites along the auditory pathway as well significant changes in other sensory systems and non-auditory regions of the central nervous system. Here we review some of the striking electrophysiological, behavioral and neuroanatomical changes that occur following various cochlear insults. A common theme that emerges from these studies is that cochlear damage, which reduces the neural output of the cochlea, often leads to sound-evoked hyperactivity along the auditory pathway, particularly at the auditory cortex, as well as behavioral evidence of hyperactivity. Surprisingly, noise-induced cochlear damage has a significant impact on cell proliferation and neurogenesis in the hippocampus, a region of the brain involved in memory and spatial navigation. The logical conclusion from decades of research is that peripheral hearing loss has profound effects on the function of the central auditory system.