The Use of Ultrasonic Bone Conduction to Treat Tinnitus Josh Vicari July 23, 2007

What is Tinnitus? Tinnitus is the perception of sound in the ears when no external source is present Typically, it is perceived as a bell-like or ringing tone however, some people report hearing sounds such as crickets, music, waves or buzzing Many people experience this condition at one point in their lives after events such as concerts however it usually disappears after hours In severe cases, tinnitus will effect the patient 24 hours a day, seven days a week Tinnitus Sample Tinnitus Sample

What causes Tinnitus Tinnitus is usually caused by a head injury, an infection, diseases ranging from the common cold to diabetes, or exposure to loud sounds such as gunshots and explosions It is estimated that in the United States alone, over 36 million people suffer from tinnitus. Around 10 million of these people have a severe case

It can also be a sign of hearing loss. People who work with loud equipment, such as power tools, commonly develop the condition The cochlea contains thousands of tiny hairs which vibrate in response to sound waves and cells which convert neural signals back into acoustical vibrations. The sensing cells are connected with the vibratory cells through a neural feedback loop, which is regulated by the brain. This loop is normally adjusted just below the onset of self- oscillation, which gives the ear its spectacular sensitivity and selectivity. If something changes, it's easy for the delicate adjustment to cross the barrier of oscillation and tinnitus results. Evidence has been found that the brain reprograms its nerve cells based on sensory loss. If the brain changes its response as a result of some hearing loss, then this could be the cause of tinnitus.

Current Tinnitus Treatments There are many different forms of tinnitus treatments available today for patients ranging from herbal remedies to cochlear implants With most methods of treatment, a great deal of time and patience is required for the therapy to be effective

Bone Conduction Conduction of sound through the bones of the skull to the inner ear A transducer is used to convert an electrical signal into mechanical vibrations Vibrations are conducted through the skull bones to the cochlea, which interprets and sends the signal to the brain

Why Use Bone Conduction? Humans typically cannot hear ultrasound ( > 20 kHz) through basic air conduction, but can perceive sound at frequencies up to 108 kHz through bone conduction It has been suggested that the reprogramming of the brain could be reversed with high frequency stimulation. Bone conduction has many applications in the medical and communications industries such as headphones, hearing aids, cell phones, and communications systems used in high-noise environments

The Tests Used Kyma X and the Capybara 320 to run tests Kyma X allows us to adjust sound filters and the value of the ultrasonic frequency

Amplitude Modulation (AM) Variation of the amplitude of a carrier wave that is of a carrier wave that is multiplied (modulated) multiplied (modulated) with an input signal with an input signal When the carrier wave is modulated with the input modulated with the input signal, it’s amplitude varies signal, it’s amplitude varies in the same manner as the in the same manner as the input input

AM in Frequency Domain Frequency components of the input signal are reproduced at the carrier frequency

The Tests Live input given to subject in sound booth Subject wore headphones which gave clean signal, and a transducer which delivered processed signal Objective was to make speech sound as intelligible and pleasant as possible so that patients will stay with treatment The longer a patient undergoes therapy, the better

What We Tried Searched for proper filtering algorithms and appropriate value for carrier Multiple Carriers at different values – decreased intelligibility Placement of Ultrasonic Transducer – depends on individual Number of Transducers (one vs. two) – one was easier to understand; the two transducers seemed to produce an echo or delay within the head

Sine Wave vs. Square Wave “jar”

Carrier Suppression “twins”

Our Device

The Not-So-Secret Part

References M. Lenhardt et. al. High Frequency Sound Treatment of Tinnitus VCU. 22 July M. Lenhardt et. al. Human Ultrasonic Speech Perception. Science. 253, (1991). About Tinnitus American Tinnitus Association. 22 July < M. Lenhardt et. al. Tinnitus Improvement with Ultra-High-Frequency Vibration Therapy. International Tinnitus Journal. 11, 1, (2005).

Acknowledgements Dr. Martin Lenhardt, mentor Alan Madsen Josh Slane Dr. Allison Johnson and the Howard Hughes Medical Institute