Auditory Brain Implants

by Bridget D. Garza, Interim Executive Director

“Imagine a world without sound. A remote, silent

KEY

1. TYMPANlC MEMBRANE

landscape void of normal

2. OSSICLES

conversation and music.” his phrase is taken from The EAR Foundation brochure called “the Gift of Hearing”. Imagine not being able to hear the birds singing early in the morning or a favorite song on the radio. For an estimated 28 million Americans afflicted with hearing loss, this silence can be overwhelming. For most Americans with hearing loss there is hope either through the use of Hearing Aids, Assistive Listening devices (ALDS) or Cochlear Implants. But; for a small percentage of people who suffer from Neurofibromatosis Type 2, (pronounced Neuro-fi-bro-ma-to-sis, NF2 for short), a genetic disorder that affects one in 40,000 people in the United States, hearing loss is inevitable. Neurofibromatosis, a hereditary genetic disorder causes tumors to form on the nervous system anywhere in the body at any time. NF2 is characterized by bilateral acoustic neuromas (benign tumor growth) on both auditory (hearing) nerves.(figure 1) Even though not malignant, left untreated the tumors will continue to grow and destroy hearing. As the tumor expands, the patient begins to experience hearing impairment, tinnitus, fullness in the ear, imbalance and facial numbness or twitching. Continued growth

3. 4. 5. 6. 7. 8. 9.

SEMICIRCULAR NERVE COCHLEA VESTlBULAR NERVE COCHLEAR NERVE FLOCCULUS ACOUSTIC NEUROMA FACIAL NERVE

Figure 1

would eventually cause death. The most common solution for NF2 patients is to have these tumors removed by surgery. When the tumors are identified early surgery can sometimes conserve hearing. In many unfortunate cases the hearing nerve cannot be separated from these locally aggressive tumors. During surgery the auditory nerve is severed rendering the patient totally deaf. After 30 years of development and research, in June of 1994 the Food and Drug Administration (FDA) granted an Investigational Clinical Trial of a Multichannel Auditory Brainstem Implant (ABI). What is so fascinating about the ABI? It submits sound information directly to the brain, bypassing the inner ear and the auditory nerve. In 1995, The Otology Group under the direction of The EAR Foundation’s President, Dr. C. Gary Jackson and President Emeritus, Dr. Michael E. Glasscock received an invitation to serve as one of the Ear Centers to participate in the clinical trial of the Multichannel Auditory

Brainstem Implant. There are only 10 Ear Centers nationwide. Since 1996 The Otology Group has performed six ABI operations. Being awarded the honor as one of the medical institutions to conduct a clinical trial did not come without a price. Since this was an investigational clinical trail, the patients’ insurance companies did not cover the cost of the ABI units. In 1995 The EAR Foundation organized a fund raising campaign to raise $80,000 to cover the cost of the ABI’s. A gracious benefactor pledged $40,000 in a matching grant, which meant The EAR Foundation, needed to raise $40,000. Within six months the funds were raised to purchase the Auditory Brainstem Implants. The ABI surgical procedure is a long and complex operation. The Nashville implant team consists of Neurotologist, Dr. Gary Jackson, Neurosurgeon, Dr. Carl Hampf and Audiologists, Anne Forrest Josey Tallent, M.S. and Susan Amberg, M.A. Continued on page 4

Auditory Continued from page 1 The surgery begins by having one of the acoustic tumors removed, which requires an incision behind and around the ear. Next the process involves removing a segment of the bone to remove the tumor from the auditory nerve, and it is here that the auditory nerve is sacrificed in the larger tumor operations. After removal of the acoustic tumor, the Electrode Array (figure 2) which is flat to conform to the brainstem is surgically placed on the cochlear nucleus region of the brainstem near the point where the auditory nerve has been severed. This region is composed of complex layers of auditory neurons, each specializing in different functions and each with its own pitch organization. The electrode array stimulates this group of auditory neurons or nerve cells in the brainstem. The Electrode Array leads out to the surface of the skull where an internal receiver is placed. (figure 3, #6) The pathway of a sound for those with an ABI is as follows: Sound is received by a microphone worn behind the ear and is transmitted to a speech processor. The speech processor transforms acoustic information into a digital signal (in other words, useful sounds are coded). The useful sounds are then relayed to an external transmitter, also worn behind the ear, and across the skin to an external receiver (decoding chip), that converts the sounds into electrical signals. The signals are then sent to the internal receiver and down the electrodes to the Electrode Array, which then stimulates the auditory region of the brainstem. From there, the sound information is transmitted to the brain for interpretation. (figure 3). This sequence of events happens within microseconds. Even though the “pathway of sound to the brain” takes seconds, the stimulation, programming, evaluation, and rehabilitation period of the ABI for the average patient is a year.

Brainstem lmplants

Figure 2

Approximately eight weeks are allowed for healing before the patient sees the Audiologist to begin. Initial stimulation, programming, and evaluation of the ABI takes place over a three-day period. Due to the proximity of the brainstem electrodes, there is a small risk that electrical stimulation may compromise heart function. Therefore, the initial stimulation of the electrodes and programming are conducted in the hospital, in the presence of medical staff qualified in resuscitation and with the patient connected to ECG monitoring equipment. On the first day of the initial stimulation, each electrode channel is turned on, and the stimulation level is increased until the patient indicates they can barely hear the stimulus tone (threshold or T-level). Stimulation is then increased until the patient indicates the loudness of the tone is slightly loud, but still comfortable to listen to (comfort or C-level). The patient then makes sure all the channels have equal loudness. Following this, the patient must determine the pitch order of the channels (from low to high pitch) and if each channel has a different pitch. Once all this information has been obtained, a MAP (or program) is created which tells the speech

processor how to encode the sounds it receives and then transmits to the electrodes. Some adjustments may need to be made to the MAP to ensure the best results for the patient. The second and third days of the initial stimulation are for evaluating the patient’s performance with the ABI to obtain a performance baseline for comparison with results in the future. Patients are given tests that assess if they can: 1) identify environmental sounds, 2) distinguish between single-syllable and multiplesyllable words, and 3) understand speech stimuli presented in auditory only, visual cues only, and auditory plus visual cue conditions. Some of the tests are “closed-set”, meaning that the patient has a limited number of responses to choose his answer from, while others are “open-set”, where the patient is given no assistance in choosing a response. The FDA study requires that the ABI patients return for evaluation at three months, six months, nine months and one-year intervals after the initial stimulation. Evaluations are done on an annual basis following the first year. The procedures for these evaluations are the same as for the initial evaluation, with the exception of any adjustContinued on page 5

Auditory Brainstem Implants Continued from page 4 ments to the MAP being done at the end of the evaluation rather than at the beginning. This is because it takes time to adjust to changes made in the MAP, and we want to assess patient benefit with a MAP with which he is familiar. Worldwide, more than 92 patients have undergone surgery in which the acoustic neuroma (tumor) has been removed and the ABI implanted. Preliminary results from the ABI research subject indicate that: 83.2 % Receive stimulation 88.0 % Who receive stimulation show improved lip-reading abilities 14.3 % Within the year demonstrate

sound-only sentence recognition (This percentage of patients were able to converse on the phone)

16.7 % Do not receive any stimulation

Reports vary to some degree, but generally everyone says speech has a muffled sound quality, like a towel over a loudspeaker, or like someone trying to talk without opening their mouth. In 1996 The Daily Iowan reported on a 41-year-old male having a successful Brainstem Implant. The patient, a senior program analyst, had been deaf for 18 years. His doctor reported that “he was able to hear his daughter play the violin shortly after having the surgery,” and at the time was making progress with interpreting sounds as words. Another ABI patient exclaimed, when she goes dancing she can hear the beat of the music. She thought she would never dance again. The overall expectancy from the ABI is that the patient will be able to detect sound at normal conversational levels and lip reading abilities will improve. As one ABI patient stated “I can pick out the number of syllables in each word, and that helps me to understand speech better.” In a 1996 Nashville Banner article, Senior Medical Writer, Bill Synder wrote, “Brain implant testing may open “new vistas” of hearing.”

Dr. Jackson firmly believes that the research and surgery that is being done today will open “new vistas” References:

Bill Synder, “Brain Implants Testing By Area Dots May Open “New Vistas” of Hearing”, The Nashville Banner, March 12, 1996, Medical News Section. Investigational Use Only Brochure, “Multichannel Auditory Brainstem Implant,” Englewood, Colorado, Cochlear Corporation, 1995, March 1999. Mike Waller, “Doctors Work To Help Deaf Man Hear”, The Dailey Iowan, October, 17,1996, Page 1A.

for treatment of some types of hearing loss with the coming of the new millennium. q Steve Otto M.A., “The Auditory Brainstem Implant,” The NF2 Review, April 1994, Pages 1,6,7. Jenny R. Hendricks, “Autobiography of Two Multichannel ABI Recipients,” Cochlear Corporation, 1996. ‘What is NF?“, Neurofibromatosis, Inc. Homepage, www.nfinc.org, April, 1999.

“Some Answers About Acoustic Neuroma” Brochure, Acoustic Neuroma

Association, January, 1993. (404) 237-8023.

Susan M. Amberg, M.A., CCC-A, “Auditory Brainstem Implant Rehabilitation,” April, 1999.