The Sensory-Neural Tango
So how does the central auditory nervous system react when the periphery stops working. The simplistic view of the distant past would suggest that the neural centers between the ears and the brain are nothing but way stations through which information is passed without much additional processing. Over the years we have learned that these way stations perform important steps of feature extraction, temporal coding, and integration of information between ears. We have also started to understand the important plastic changes that happen in the auditory centers of the brain when the information stream from the periphery is halted. All this knowledge notwithstanding, much remains to be learned about the exact nature of the interaction between the auditory periphery and the different layers of the auditory nervous system in the brainstem, midbrain, and cortex.
A new paper by a group of scientists from the Eaton Peabody Laboratories at Harvard sheds new light into the complex interaction between the auditory periphery and various neural centers. The scientists selectively removed 95 percent of the cochlear afferent responses in groups of mice. As expected, otoacoustic emissions remained intact and auditory brainstem responses were severely affected. Now comes the surprising part, the severe dysfunction of the auditory nerve, resulted in a bigger (yes, you read it correctly) response in the cortex, thereby compensating for the peripheral loss. As a result, tone detection remained unaffected. However, the cortex was unable to compensate for tasks that involved coding based on temporal processing. These results portray a striking resemblance to what we encounter in the clinic in cases of auditory neuropathy spectrum disorders and other forms of central auditory processing disorders, making them highly relevant to the practicing clinician.
Interestingly, this year's Academy Research Conference (Wednesday, April 13, in Phoenix) is on Central Auditory Processing Disorders. Leading scientists and clinicians will present their work in the format of a day of lectures and over forty posters.
Chambers AR, Resnik J, Yuan Y, Whitton JP, Edge AS, Liberman MC, Polley DB.
Central Gain Restores Auditory Processing following Near-Complete Cochlear
Denervation. Neuron. 2016 Jan 28. pii: S0896-6273(15)01169-1. doi: