by Kimberly Allen, RN
Auditory Brainstem Implants (ABIs)
Auditory brainstem implants or ABI’s have been in use since 1979. However, though they have been approved for use in children in Europe so far they have only been approved for use in adults in the US. There have been approximately 1,000 ABI’s implanted in hearing impaired people worldwide. Now, a 3 year old boy named Grayson Clamp is the first child in the US to receive an ABI.
Grayson is participating in the very first FDA approved clinical trial using the ABI in children. The trial is sponsored by the House Research Institute along with Children’s Hospital Los Angeles and Vittorio Colletti, MD from the University of Verona Hospital, Verona, Italy. The House Research Institute developed the ABI. It is the first successful prosthetic hearing device in the world that is able to bypass both the inner ear and the auditory nerves completely directly stimulating the nerves at the brainstem. According to executive vice president for research Neil Segel PhD, “this study has the potential to expand the use of this remarkable device, which represents the only effective sensory prosthetic for direct brain stimulation in use today.”
Grayson was born without the auditory or cochlear nerves that transmit the sound signals between the brain and the inner ear. A cochlear implant was tried, however, because there are no nerves to transmit the signals from the implant to the brain it didn’t work. So what is an ABI? It is an electronic device that allows people like Grayson that were born without auditory nerves as well as people diagnosed with neurofibrmatosis type II to hear the sensation of sound. Part of the device is a micro chip that is placed on the brainstem allowing the sound signals to completely bypass the cochlear and auditory nerves, the second part is worn externally behind the ear. Though these devices have been able to return some hearing to adults researchers are very excited about the potential in children. Dr. Craig Buchman from University of North Carolina, the surgeon in charge of Grayson’s implant, states that “children have enormous potential because of their brain plasticity”. He went on to say that they also have enormous potential to interpret sounds. The reason Grayson was chosen to be the first child to receive the implant is because of his high cognitive abilities. He already uses cued speech which is a visual system based on the sounds used to communicate. This will enable Dr’s to see how he is hearing and responding to sound stimulation. Because the ABI delivers the pattern of sound signals very differently than the natural acoustic pattern the brain must learn these new patterns. The brains in children are very adaptable and researchers are confident that their brains will be able to interpret the information and that many will also be able to learn to speak as well as understand sounds.
So how does the ABI work? First the microphone worn on the outside of the skull behind the ear picks up the sound and the cable then sends it to the speech processor. The speech processor then filters and analyzes the various sounds coding them into digital signals. These digital signals are then sent back along the cable to the transmitting coil. The digital signals are then sent by the transmitting coil to the implant under the skin. The implant then sends the signals to the electrodes on the cochlear nucleus. The electrodes then stimulate the cochlear nucleus which in turn produces a stimulation that can be interpreted as sound. This process occurs at the same speed as though it were traveling the normal route via the auditory and cochlear nerves so your child will hear sounds when they occur.
The process of learning to hear with an implant can take several weeks or even months. For most at first the sound is very strange and they don’t understand the meaning behind it. In fact in the beginning many noises sound the same making it difficult to determine what is being heard with the ABI. It’s important to remember each case is different, some people have only an awareness of sound after receiving the ABI while others hear nothing at all after receiving the implant. So far for Grayson the ABI seems to be working which could be a great indicator of potential success in children.
Cochlear implants are not hearing aids. Hearing aids amplify sound so that someone with mild to moderate hearing loss can hear better. A cochlear implant is a small electronic device that is surgically implanted. Since the development of the cochlear implant approximately 220,000 people worldwide have received them. Approximately 43,000 adults and 29,000 children in the US have received cochlear implants. They are currently approved by the FDA for use in people from 1year of age and up. However, in the US they have been implanted in children as young as 6 months of age as well as children as young as 4 months of age internationally.
Cochlear implants were created for adults and children that suffer from a form of hearing loss known as sensorineural hearing loss. In sensorineural hearing loss there is usually damage to the tiny hair like cells in the cochlea. The cochlea is the tiny snail shaped coil in your inner ear that transmits sound signals to the auditory nerve. When the tiny hair like cells in your cochlea are damaged they are unable to transmit the sound signals to the auditory nerve. The cochlear implant circumvents the cochlea’s tiny hair like cells and directly stimulates the auditory nerve.
So how does the cochlear implant work? First a tiny receiver is implanted just under your skin behind the ear. This receiver is then connected to tiny electrodes that have been placed in the cochlea. You are then fitted with an external auditory speech processor, a transmitter and a battery pack. The microphone looks like a hearing aid and is worn behind the ear or it can be worn somewhere else on your body depending on your age activity level and lifestyle. Once your implant has been activated, which is usually a week or two after surgery the microphone will detect sounds and transmit them to the speech processor which then interprets the sounds and turns them into an electrical signal. The speech processor then sends the electrical signal to the implant which decodes it. The implant decides how much of the electrical signal should be sent to the nerve endings in the cochlea. The sounds pitch is determined by the amount of electrical signal that is sent to those nerves which then sends the signal along the auditory nerve to your brain. The brain then interprets the signal giving you the ability to hear.
The cochlear implant will not restore normal hearing, it can provide you with a functional representation of sound. The sound is usually described as a “mechanical” sound, however, over time your brain is able to adapt to the new sound”. Cochlear implants can be a life changing device for many people with hearing loss that can not be managed effectively with hearing aids. Once you become accustomed to using the cochlear implant most are able to understand speech as well as interpret everyday sounds in their environment. Some people are able to enjoy listening to music as well as have phone conversations.
So who is a good candidate for a cochlear implant? The best candidates are children and adults that have experienced recent hearing loss as well as young children with hearing loss that has been identified very early. People that were able to hear as well as children that were born deaf and receive a cochlear implant before 5 years of age do very well. Over time with rehabilitation they are able to develop a very good understanding of speech as well as the ability to speak. Children that receive an implant before 2 years of age do even better than children that receive their implant between 2 and 5 years of age. Most children that receive their implants early in childhood are able to attend conventional schools.
While cochlear implants can significantly improve the quality of life for many adults and children with profound hearing loss they are not for everyone. If you or your child has missing or damaged auditory and/or cochlear nerves the cochlear implant will not be effective because it is designed to bypass the cochlea and directly stimulate the “hearing nerves”, If there are no viable nerves to transmit the signals to the brain it will not provide the sensation of sound. If this is the case for you or your child there are other options available including auditory brainstem implants.
Kimberly Allen is a registered nurse with an AND in nursing. She has worked in ACF, LCF and psychiatric facilities, although she spent most of her career as a home health expert. She is now a regular contributor to HealthAndFitnessTalk.com, dispensing advice and knowledge about medical issues and questions. You can reach her with any comments or questions at firstname.lastname@example.org.