PATIENT RECEIVES THE FIRST SUCCESSFUL BRAIN IMPLANT OF HMRI-DESIGNED MICROELECTRODES TO RESTORE HEARING

A system of microelectrodes developed by Pasadena's Huntington Medical Research Institutes (HMRI) has been successfully implanted in a patient by surgeons at the House Ear Clinic in Los Angeles.  The electrode array, called a Penetrating Electrode Auditory Brainstem Implant (PABI), is placed into the hearing portion of the brain (the cochlear nucleus) and stimulates the brain to restore some degree of hearing to people who are profoundly deaf. This success caps a 15-year joint effort by scientists, engineers and physicians of HMRI, the House Ear Institute (HEI) and Cochlear Limited in Sydney, Australia. Douglas B. McCreery, Ph.D., director of HMRI's Neural Engineering Laboratories, headed the project.  The National Institutes of Health provided funding. 

The new electrode array is an improvement of an existing Auditory Brain Implant (ABI) which was approved by the FDA in 2000 and has been implanted in more than 200 patients.  The PABI is designed primarily to restore useful hearing to  patients in whom both auditory nerves have been destroyed by tumors of the 8th cranial nerves (vestibular schwannomas), and who therefore cannot benefit from cochlear implants.  According to Dr. McCreery, Type II Neurofibromatosis (NF2) is the most common medical condition that results in destruction of both auditory nerves. A cochlear implant (one which stimulates the cochlea, or inner ear) cannot be used because the auditory nerve is not able to carry signals from the cochlea to the cochlear nucleus in the brainstem.

The PABI system consists of an external sound processor and transmitter, and an internal receiver and stimulating unit.  It is manufactured by Cochlear Limited. In the new device, the microelectrodes that activate the neurons are about the size of a human hair, and reach into the brainstem and directly into the cochlear nucleus itself.  This feature allows the device to selectively translate high-pitched sounds into activity in the neurons in the cochlear nucleus that normally respond to high-pitched sounds, and conversely for low-pitched sounds. The older version of the ABI is not able to achieve this selectivity, since the stimulating electrodes are placed only on the surface of the brainstem. Users should have improved speech recognition as well as the ability to identify environmental sounds, such as telephones or street noises, and thereby improve their safety and quality of life.   "We hope that speech comprehension will be closer to that experienced by multi-channel cochlear implant users," said Robert Shannon, Ph.D., who heads the portion of the project that is based at the HEI, and who developed all of the methodology used to evaluate the patient's ability to perceive speech and environmental sounds.

Surgeons William Hitselberger, M.D., and Derald Brackmann, M.D., implanted the device into a patient on November 19, 2003, and, after allowing time for surgical healing, audiologists at the HEI tested its effectiveness by activating the electrodes on January 12. Patients with the older version of the auditory brainstem implant require some time to become accustomed to the device, and only time will tell how well the patient with the new device will eventually be able to understand speech.  However, after the device was activated, the lively, outgoing woman patient responded: "I'm just blown away by this technology.  I can hear again!"

Penetrating microelectrodes for stimulation of the human cochlear nucleus and other parts of the brain have been under development for more than 15 years at HMRI.  The PABI microelectrode arrays are assembled at Cochlear's engineering and manufacturing facilities, according to the physical dimensions and specifications developed by HMRI's McCreery and HEI's Jean Moore, Ph.D., and using iridium microelectrodes developed and fabricated at HMRI.  Dr. McCreery also designed an insertion tool that is used to implant the arrays of microelectrodes into the brain.  Safety studies of both the electrodes and the insertion process were performed at HMRI. HMRI Executive Director William Opel, Ph.D., said of this encouraging development, "This breakthrough is the result of two decades of HMRI research and development by dedicated scientists and technicians, supported by generous donors and the excellent NIH grant funding."

This project was funded in part with Federal funds for the National Institute on Deafness and Other Communication Disorders (NIDCD), National Institutes of Health (NIH), under Contract No. NO1-DE-1-2105.  Total NIDCD/NIH funding since June 1992 is $4,851,293.  Funding to Cochlear Limited from the FDA was $300,000.