Surmounting the acoustic barrier with neural implants and the bionic ear

The advanced technology of cochlear implants has successfully managed to integrate people with hearing loss into normal society and provide them with a highly productive quality of life.

September 09, 2023 11:58 am | Updated September 14, 2023 10:50 pm IST

Representational image of the bionic ear in a petri dish. FIle

Representational image of the bionic ear in a petri dish. FIle | Photo Credit: AP

The burden of hearing loss in India is significant as it is one of the most common congenital anomalies to affect children. The World Health Organisation reports that severe to profound hearing loss affects nearly 2 - 3 per 1000 live births, making it the most common congenital abnormality to affect newborns the world over. This scenario is even more pronounced in developing countries such as the Indian sub-continent, especially with the continuing problem of consanguinous marriages. Hearing loss at birth is considered a social stigma even in present-day society and results in a double tragedy, as it leads to not only deafness but also speech and language deprivation and communication problems. 

In the past, individuals with severe to profound hearing loss with no benefit from hearing aids were condemned to live in a world of silence. However, hearing loss today, is the only truly remediable handicap, due to remarkable advances in biomedical engineering and surgical techniques. Rather than mend a diseased organ, the emphasis has shifted to bypassing it with a bionic prosthetic device.

Cochlear implants (CI) can help deafened individuals living in a world of silence enter the world of sound. The advent of this technology has successfully broken the acoustic barrier, thus integrating people with hearing loss into normal society and providing them with a highly productive quality of life. 

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CIs help augment or restore hearing by integrating with an external circuitry with the peripheral hearing apparatus and the central circuitry of the brain. They are bio-compatible and safe as well as extremely effective in restoring hearing to both children and adults with severe - profound hearing loss, who do not receive benefit from conventional hearing aids. These implantable devices electronically stimulate the cochlear nerve (nerve of hearing), bypassing the damaged hair cells of the cochlea (inner ear). Thus, hearing restoration is the first successful attempt in medical science to integrate an electronic device with the central nervous system, in order to fully restore a lost special sense organ. 

CIs are electronic devices with external and internal components and are designed to detect mechanical sound energy and convert it into electrical signals that can be delivered to the cochlear nerve. These electrical signals are processed by an external speech processor and sent via a radiofrequency interface into an array of electrodes implanted surgically within the cochlea (inner ear). 

The individual’s ability to adjust to, interpret and respond to the electrical stimulus can determine outcomes. Length of time spent without sound stimulation, presence or absence of previous experience with sound, personal motivation, community or family support, and opportunities for habilitation have been shown to be important factors in achieving a good outcome. Early identification and management of hearing loss is extremely important for good outcomes with a CI. All children below the age of six years who have profound hearing loss and who will not benefit from conventional hearing aids and all adults who have lost hearing after the acquisition of language are ideal candidates. Presently, the indications for CI have expanded to include children aged one year or less, elderly individuals, children with abnormal cochlea, additional handicaps, etc. 

The recent trend is towards cochlear implantation in both ears which provides improved localisation of sound and enhanced ability to hear in the presence of background noise. For long it was believed that natural hearing was not compatible and could not co-exist with bionic hearing through a cochlear implant. This myth has fortunately been laid to rest in recent years with the advent of electro-acoustic stimulation (EAS) or hybrid implants. This application of implantable hearing technology combines a hearing aid and a cochlear implant (EAS) into a hybrid device designed for individuals with low-frequency hearing and severe-to-profound high-frequency hearing loss. 

Cochlear implant electrode array in situ

The switch-on of the device is done three weeks after surgery once the wound has healed. Mapping is done at periodic intervals and prolonged and intensive habilitation after cochlear implantation is essential. Habilitation aims at improving receptive language skills and expressive skills. 

In Tamil Nadu, the cochlear implant program has been very successful as free cochlear implants are being sponsored to children under the age of six years and below the poverty line. Nearly 5000 CIs have therefore been performed in Tamil Nadu under the Chief Minister’s Comprehensive Health Insurance Scheme. 

CI surgery and technology continue to evolve. Rapid technological advancements in bioengineering and implant manufacturing methods have led to miniaturization of the device, with refinement in sound signals, providing better “hearing in noise” and music appreciation among cochlear implantees. Robotic techniques for surgery may be available in the near future. Fully implanted devices, improved speech coding strategies, nanotechnology, stem cell therapy, cochlear hair cell regeneration, and nerve growth factors used in conjunction with an implant may be available in the future. Rapid advances in genetics are revolutionizing our understanding of congenital deafness and should play an important part in prevention, in the selection of patients and in determining CI outcomes.

Gene therapy for hearing impairment may become available. A novel imaging technique, synchrotron radiation phase-contrast imaging to look into the interior of the cochlea with unprecedented detail will result in an improved understanding of the microanatomy of the ear and improve management of hearing loss. Artificial intelligence is also playing an important role in improving patient outcomes. 

The cochlear implant is one of the most significant innovations of the last century making hearing the only sense that can be replicated through a medical device. Developments in technology will expand the benefit of cochlear implants. A full spectrum of hearing solutions is now available in the Indian subcontinent.  Despite several challenges, cochlear implantation in India is a success story.

(Prof. Mohan Kameswaran is Senior Consultant ENT Surgeon & Managing Director, Madras ENT Research Foundation, Chennai. merfworkshop30@gmail.com)

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