Electrical Stimulation for Suppression of Tinnitus
by Barry Keate
Since the invention of the battery in 1801, researchers have been looking into methods to suppress tinnitus electrically. In 1802 a German physician by the name of Grappengeiser connected a battery to deaf patients who had tinnitus… and threw the switch.
The results were mixed but he described a phenomena that is still true today. He found that in order to suppress tinnitus he had to connect the positive electrode of the battery to the ear. If the negative electrode was placed on the ear, the tinnitus was not suppressed and the patients heard additional sounds.
After alternating current (AC) was invented in 1831, various researchers began investigating it’s effects. One French physician claimed an 80% cure rate for his patients, however little specific information was offered.
During the latter half of the 19th century, various investigators worked on the treatment of tinnitus using either AC or direct current (DC) with mixed results and very little documentation. Around the turn of the century, publication of work exploring electrical suppression of tinnitus ceased entirely, not to be rediscovered until the 1960s. Many of the characteristics of electrical suppression of tinnitus described in the 19th century were duplicated in more recent controlled experiments.
In 1960, American scientists Hatton, Erulkar and Rosenberg were exploring the physiology of the vestibular, or balance, system using DC electrical stimulation. They found that almost half their deaf patients reported a reduction in their tinnitus during stimulation. This rediscovery sparked a renewed interest in this area and since then, there has been a wealth of research and scientific interest in electrical suppression.
Two critical differences among researchers are the type of electrical stimulation used and the location where it is delivered. Since 1802, it was known that DC current was most effective. Several major problems prevented it from becoming routine clinical practice. The first and most critical, is that DC current effectively destroys hearing so it can only be used on profoundly deaf people. The second is that the electrode has to be placed near the inner ear, which means going through or under the ear drum. This can only be accomplished in a clinical situation and requires a minor surgical procedure. Third, suppression of tinnitus only lasts as long as the current is applied; when it stops, the tinnitus returns.
Between the 1960s and 1990s, numerous studies have been conducted with electrical suppression. The type of current, duration, placement and criteria for success were different in each of them. Researchers in many countries applied their own best guesses as to how to conduct the studies. Results were highly irregular, with some studies having a high rate of success and others little or none. The one common element seemed to be that DC current was more successful but always destroyed hearing in the subjects. For this reason, DC studies were always conducted on profoundly deaf participants.
A wearable device known as the Audimax Theraband was studied by Abraham Shulman, MD, in 1985. This device delivered low level, undetectable AC current to the mastoid bone behind the ear. The frequency of the stimulation systematically swept from low (200 Hz) to high (20,000 Hz). In the first study, Dr. Shulman reported that 54% of participants (7 of 13 participants) experienced decreased tinnitus and 8% got worse. In a second study of the same device 67% (8 of 12) reported suppression with 25% (3 of 12) reporting complete suppression and residual inhibition. Despite these very encouraging results, subsequent trials were unable to reproduce them and the device is not in use today.
Also in 1985, Drs. Engelberg and Bauer stimulated 10 patients with a hand held probe at thirteen locations on and around the external ear. Each stimulation lasted for two minutes, three times per week for up to seventeen sessions. Although the investigators did not precisely define what they considered to be improvement, they reported that 60% reported subjective improvement lasting from a few hours to several months. In a second, more controlled follow up, 20 patients were divided into two groups, half of which received the treatment and half of which received a placebo. 90% receiving treatment reported improvement while 10% of the placebo group improved.
Notwithstanding these accomplishments, the successful use of AC current continued to be inconsistent. Many studies were conducted that could not duplicate the positive results of the previous ones.
Unlike the mixed results obtained through electrical suppression, electrical stimulation for the restoration of hearing through a device known as a cochlear implant has been applied successfully in more than 14,000 patients worldwide. The implant receives sound through a microphone, converts it to an electrical signal, processes the signal to enhance specific characteristics and delivers the signal through one or many electrodes that are surgically placed in the inner ear. This stimulates the hearing nerve, resulting in the perceived reception of sound by the patient.
Early implants in the 1970s and 80s used only a single electrode. These single channel implants did not allow patients to understand speech without lip reading. More sophisticated implants, with up to 22 channels, were developed in the mid 1980s and allow the patient to more clearly understand human speech.
One positive side effect of the implants has been to reduce tinnitus in many patients. Many studies have been conducted and the results are very consistent. Reports of decreased tinnitus range from 60% to 92% in all the studies. It is still unclear whether the electrical stimulation from the electrodes is reducing tinnitus in these patients or whether listening to environmental sounds and speech is masking the tinnitus.
One of the major stumbling blocks of this technology, as it applies to tinnitus sufferers, is due to the invasive nature of the procedure. Once the implant is introduced into the inner ear, all remaining hearing is completely destroyed. The insertion of the electrode array completely destroys any remaining hair cells in the inner ear. Because of this, cochlear implants are strictly limited to those with profound hearing loss.
The Future of Electrical Suppression
There has been a multitude of new studies proceeding on the basis of lessons learned from the past and cochlear implants. Drs. RL Steenerson and Gaye Cronin at the Atlanta Ear Clinic have conducted a study of five hundred patients using a probe type stimulator. They report that 53% of patients showed decreases in their tinnitus on a subjective rating scale. After a 3 month follow-up, 72% had no loss of benefit. Thirteen patients had temporary increases and two patients had permanent increases in tinnitus symptoms. Biofeedback is typically used in conjunction with the stimulation. Biofeedback teaches people to consciously control bodily functions previously thought to be beyond the control of the conscious mind. The person can then learn to relax muscles in the head and neck and increase blood flow into the inner ear.
Editor’s Note: Increasing blood circulation into the inner ear is one of the effects of using Arches Tinnitus Relief Formula®. A combination of electrical suppression and Arches Tinnitus Formulas will increase the benefit of both.
The Atlanta Ear Clinic defines success by a reduction of 2 points or more on a scale of 0-10. During each treatment the patient receives an AC electrical current for 45 to 60 minutes on the pinna , the outer ear flap. If the tinnitus does not respond after the first six treatments, the therapy is usually discontinued.
A new study, being conducted by Dr. J. Rubinstein at the University of Iowa, has just begun. The eighth nerve is the hearing nerve and is the noisiest, or most spontaneously active nerve, in the body. Dr. Rubinstein reasons that the spontaneous activity of this nerve is likely to be minimal or absent in tinnitus patients who have significant hearing loss and that may be why they are experiencing the abnormal sensation we call tinnitus. He is therefore attempting to supply electrical stimulation to duplicate the missing neural activity. Restoring this activity may restore a more normal input to the patient’s auditory system and possibly reduce or eliminate the tinnitus. His work involves a transtympanic stimulation using an electrode located at the round window. Various types of electrical pulse trains will be used to evaluate the effects of different patterns of stimuli.
There’s a final note on a coincidental discovery that may be very important in the future. William Martin, Ph.D at the Oregon Hearing Research Center has been working with a neurosurgeon who implants very fine electrodes deep into the brain. These electrodes introduce electrical stimulation to help people control movement disorders such as severe Parkinson’s disease. The patients can use remote control devices to turn on the stimulation whenever their motor symptoms become unusually severe.
Dr. Martin thought to ask these patients if any of them had tinnitus. It turned out that seven of them did and three told him that when the electrodes were activated they had marked improvement in their tinnitus. This despite the fact that the electrodes were not located anywhere near the brain regions devoted to hearing. Dr. Martin is continuing his work with these patients who already had brain electrodes implanted. What would have happened if these electrodes were implanted in the auditory areas of the brain?
More work is needed in the future to locate the brain area or areas that are specific to hearing and tinnitus in order to study the effectiveness of electrical suppression of tinnitus directly from the brain.