Acoustic and Electrical Stimulation for the Treatment of Tinnitus

Tinnitus, or ringing in the ears, is a medical condition that significantly affects the quality of life of patients and that can be disabling to many. It has become known that acoustic and electrical stimulation of the inner ear can cause suppression and sometimes elimination of tinnitus. The long term goal of this study is to devise new methods for reduction/elimination of tinnitus. Multiple attempts at tinnitus suppression using acoustic and electrical stimulation of the inner ear has been performed with variable success. More commonly, acoustic stimulation is used to mask the tinnitus as opposed to suppressing or inhibiting the tinnitus. More recently, however, cochlear implants have been used for hearing as well as tinnitus suppression. The first hypothesis is that in using acoustic stimulation at specific frequencies and levels of loudness, tinnitus can be suppressed / eliminated. The second hypothesis is that using the same electrical stimulation technology as used in the cochlear implant, tinnitus can be suppressed/eliminated. These predictions will be tested in 3 specific aims. In Specific Aim 1, an acoustic sound will be delivered through headphones to the subjects' ears at various frequencies and loudness levels to evaluate suppression / elimination of tinnitus. In Specific Aim 2, an electrical current will be delivered to the inner ear. Pulse trains of various frequencies will be used to evaluate suppression/elimination of the ringing in the ears. Specific Aim 3. The effect of electrical stimulation on the subjects' quality of life will be measured using validated surveys.

In the past, attempts to suppress tinnitus using acoustic stimulation have succeeded in only masking the tinnitus to a limited degree. Tinnitus masking devices only camouflage the tinnitus. Patients frequently report an interference with hearing or complain that the devices only substitute one unpleasant sound for another. Additionally, the masking devices can only be used for a limited time and the patient's tinnitus often subjectively becomes worse after the removal of the device. Patients also become habituated or accustomed to the device thereby decreasing its effectiveness over time.

Attempts to suppress tinnitus using electrical stimulation have a long history. Starting in 1801 and continuing throughout the 19th century, the effects of electrical stimulation on the ear were described by several authors. Some of these early attempts showed that direct current applied to the mastoid or zygoma could suppress and possibly eliminate tinnitus in some patients. Aran et al have found that electrical stimulation of the inner ear via an electrode inserted through the ear drum can cause suppression and sometimes elimination of tinnitus.

The advent of the cochlear implant revolutionized the restoration of hearing to the deaf by electrically stimulating the hearing nerve. As a side-benefit, the cochlear implant was found to suppress tinnitus in 28% to 79% of patients. Electrical stimulation of the inner ear may have a direct electrical influence on the tinnitus generated in the inner ear, or it may have an indirect influence by creating activity centrally where tinnitus reduction occurs. The success with cochlear implants has led to a number of studies to evaluate electrical stimulation for suppression of tinnitus. These studies have used electrodes externally and internally (behind the ear drum) and various stimulus waveforms. They all suggest that in some patients, tinnitus can be suppressed and occasionally eliminated using these techniques. It is important to note that none of these studies was placebo-controlled.

Most recently in a preliminary study in 2003, Rubinstein et al, used a needle electrode passed through the ear drum to suppress tinnitus. The authors used a high pulse rate of 4,800 pulse-per- second (pps) for their electrical stimulation. They found that 5 of 11 (45%) subjects with electrical stimulation of the inner ear through the ear drum using a needle electrode showed substantial or complete tinnitus suppression with either no perception or only a transient perception of the stimulus. Three (27%) showed tinnitus suppression with the perception of the stimulus and three showed no suppression of the tinnitus. In subjects with cochlear implants, the authors used the cochlear implant for tinnitus suppression using the electrical signal sent through the implant to the inner ear. The results of tinnitus suppression using the cochlear implant were similar to the subjects without implants. Based on recent work performed on cochlear implant subjects, it has been found that low pulse rate stimulation may be more beneficial in suppressing tinnitus in cochlear implant patients. Electric stimulation will be delivered through an optically-isolated constant-current source. The maximum output will be set at 1000 microamps and be periodically calibrated to ensure accuracy. This device has been used in several previous studies on hearing perception and a similar device has been used to treat tinnitus . The device is routinely used for cochlear implant patients, but is not routinely used to stimulate people without cochlear implants (given their normal hearing status). It has been used experimentally, however, used for people with hearing loss or tinnitus.