NOVEMBER 2010 • VOL. 63 • NO. 11 New approaches to tinnitus management THE HEARING JOURNAL 21 Patterned sound therapy for the treatment of tinnitus By Kelly M. Reavis, Janice E. Chang, and Fan-Gang Zeng USING SOUND TO CURE TINNITUS Sound therapy, via either acoustic or electric stimula- tion, uses external sounds to provide short- and long- term relief from tinnitus. The interactions between external sounds and tinnitus are well established, as the external sounds can not only induce tinnitus, but can alter its perception as well. Excessive exposure to loud sounds is the single great- est risk associated with tinnitus onset, and for those with tinnitus, sound overexposure may exacerbate it. However, sounds used at safe levels can be highly beneficial to an individual with tinnitus. Sounds can not only distract a person’s attention away from tinnitus, but also affect the overall quality of the tinnitus. In some cases, people report noticeable changes in tinnitus pitch or quality following exposure to certain external sound sources. For example, a variety of sounds, ranging from con- stant, low-level background sounds mimicking running water to intermittent sounds mimicking fire crackling have been used to mask the overall perception of tin- nitus. 1 Additionally, many tinnitus sufferers who use hearing aids or cochlear implants to treat a concomitant hearing loss have reported a reduction in their overall tinnitus percept, with some even reporting complete elimination of their tinnitus. 2,3 It is not surprising, then, that sound therapy has become a vital component in most tinnitus treatment plans. Over the years we have gone from perceiving tin- nitus as a disease of the ear to understanding it as a disorder of the brain. A clear example is that some tin- nitus sufferers who have had their auditory nerve sev- ered still have significant tinnitus. While it is still generally believed that insult to the peripheral auditory system is a necessary factor in triggering tinnitus, recent evidence suggests that tinnitus is caused by abnormal activities resulting from cortical re-organization. 4 Our approach is to introduce cortically interesting sounds to positively alter these abnormal neural activ- ities for the purpose of tinnitus suppression. Different from steady-state sounds such as pure tones and noises, which produce mostly onset and offset responses in the cortex, the temporally patterned sounds we use, such as amplitude- and frequency-modulated signals, pro- duce highly synchronized and robust cortical responses. 5,6 Therefore, we hypothesize that temporally patterned sounds may be more effective than steady- state sounds in tinnitus suppression. Figure 1 shows the time waveform of a pure tone (1A) and two dynamic sounds, namely, amplitude and frequency modulation (1B and 1C, respectively). Figure 1A is a plot of a pure tone in which both the frequency and amplitude remain constant. Figure 1B is the same pure tone with amplitude modulation: The amplitude is varied over time while frequency remains constant. The degree of the amplitude changes can be described in terms of a modulation rate, or how fast the change in amplitude occurs, and modulation depth, or how much the amplitude increases and decreases. Figure 1C is the pure tone with frequency modulation: The frequency is varied over time while amplitude remains constant. Similarly, how fast the frequency varies over time can be described in terms of modula- tion rate and how much the frequency varies can be described in terms of modulation depth. These time- varying signals are interesting to the brain and evoke strong cortical responses. TINNITUS SUPPRESSION We systematically investigated to see if temporally patterned sounds would suppress tinnitus. These patterned sounds can be delivered acoustically via Figure 1. The time waveform of a pure tone (1A) is shown, along with two dynamic sounds, amplitude and frequency modulation (1B and 1C, respectively). A) Pure tone B) Amplitude-modulation C) Frequency-modulation