Cochlear Implant Also Uses Gene Therapy to Improve Hearing

The electrodes in a cochlear implant can be used to direct gene therapy and regrow neurons.

Growth factor: The cochlear nerve regenerates after gene therapy (top) versus the untreated cochlea from the same animal (bottom).

Researchers have demonstrated a new way to restore lost hearing: with a cochlear implant that helps the auditory nerve regenerate by delivering gene therapy.

The researchers behind the work are investigating whether electrode-triggered gene therapy could improve other machine-body connectionsfor example, the deep-brain stimulation probes that are used to treat Parkinsons disease, or retinal prosthetics.

More than 300,000 people worldwide have cochlear implants. The devices are implanted in patients who are profoundly deaf, having lost most or all of the ears hair cells, which detect sound waves through mechanical vibrations, and convert those vibrations into electrical signals that are picked up by neurons in the auditory nerve and passed along to the brain. Cochlear implants use up to 22 platinum electrodes to stimulate the auditory nerve; the devices make a tremendous difference for people but they restore only a fraction of normal hearing.

Cochlear implants are very effective for picking up speech, but they struggle to reproduce pitch, spectral range, and dynamics, says Gary Housley, a neuroscientist at the University of New South Wales in Sydney, Australia, who led development of the new implant.

Cyborg cavy: An Xray image shows the cochlear implant in the left ear of a guinea pig.

When the ears hair cells degrade and die, the associated neurons also degrade and shrink back into the cochlea. So theres a physical gap between these atrophied neurons and the electrodes in the cochlear implant. Improving the interface between nerves and electrodes should make it possible to use weaker electrical stimulation, opening up the possibility of stimulating multiple parts of the auditory nerve at once, using more electrodes, and improving the overall quality of sound.

Peptides called neurotrophins can encourage regeneration of the neurons in the auditory nerve. Housley used a common process, called electroporation, to cause pores to open up in cells, allowing DNA to get inside. It usually requires high voltages, and it hasnt found much clinical use, but Housley wanted to see whether the small, distributed electrodes of the cochlear implant could be used to achieve the effect.

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Cochlear Implant Also Uses Gene Therapy to Improve Hearing