About Tinnitus

Tinnitus Cause

Tinnitus is the perception of sound in the absence of acoustic stimulus.  In most cases, it is directly related to insults to the peripheral auditory system (i.e. the cochlea).  The following is a discussion of the most current understanding of tinnitus pathophysiology and is critical for understanding the basis for our tinnitus rehabilitation program. 

The auditory system is tonotopically organized, meaning the spatial relations in the cochlea that correspond to specific tones are translated into preserved neural organization patterns that are maintained throughout the auditory cortex.  This tonotopic organization is analogous to the keyboard of a piano. If you were to take the cochlear membrane and flatten it out, the location of the low tones would be where the apex of the cochlea is, and the location of the high tones would be where the base of the cochlea is.

In the auditory cortex, the brain receives a constant and steady source of neuronal input from all frequencies.  If electrodes were placed in the brain in a person with normal hearing, you would hear the steady crackling of spontaneous neuronal firing.  The way that the brain interprets sound is by picking up changes in this steady state of background firing.

There are two things that occur during tinnitus pathogenesis.  First, the spontaneous firing rate in the area in the brain that corresponds with the damaged region of the cochlea actually increases.  This region has been termed the “lesion projection zone” (LPZ).  In the piano analogy, if a set of keys on the keyboard are damaged, the insult would be reflected as a hyperactive spontaneous firing rate in the LPZ.  This hyperactivity happens fairly quickly.   

The second thing that occurs is that the tones that border the damaged zone in the cochlea become associated with the hyperactivity occurring in the LPZ.  Essentially, the tone that people hear when they perceive tinnitus actually corresponds to these border regions, the so-called “lesion edge frequencies” (LEFs).  Hence, the hyperactive spontaneous firing rate in the LPZ becomes associated with the LEFs, and the brain interprets this as the apprehension of sound, i.e. tinnitus (Figure 2).

It is noteworthy that both steps are needed for tinnitus to develop.  Further, we know that not all people with hearing loss develop tinnitus, despite clear evidence of injury to the auditory periphery.  Further, these associations can be transient in the acute setting, but not develop into permanent associations.  Most of us have had the experience of tinnitus after exposure to toxic levels of noise, but the apprehension of tinnitus is impermanent.  This aspect of tinnitus pathogenesis is the basis for our hypothesis that prompt intervention with customized sound therapy after exposure to toxic noise may actually prevent the development of clinically significant tinnitus.

There is a third component to tinnitus pathogenesis that is equally important to the above events, and this is the creation of pathologic neural networks between the auditory system and the limbic system.  It is important to note that while 10% of the population in industrialized countries have tinnitus, in only 25% of these is tinnitus considered clinically significant. Hence, it is this critical development of associations between the auditory cortex and the limbic system that differentiates the simple precept of tinnitus from clinically significant tinnitus.  The goal of tinnitus rehabilitation is the eradication of these pathologic neural networks.

Customized Sound Therapy

Sound therapy in tinnitus management (i.e. masking) is the strategy of presenting an external sound to induce suppression of the spontaneous firing in the LPZ, and hence provide tinnitus relief.  Traditional (non-customized) masking efforts have presented broadband noises, most typically white noise.  However, it is established that targeted (customized) acoustic energy at the LEF provides more effective masking than broad-based acoustic energy.  In other words, the more closely the masking sound corresponds with the LEF, the more effective is the tinnitus suppression.

Another disadvantage to traditional “non-customized” masking strategies is that because they use broadband noise, they essentially cripple the subject while the masking therapy is being used.  This sets limits on the amount of time a subject is able to have the hyperactivity in the LPZ suppressed, and ultimately, on the rate and degree of tinnitus rehabilitation.

The BeyondTinnitus Therapy Program is designed to address all levels of tinnitus pathology.  It is a two stage program. 

Our Solution

Harmonic Sound Therapy

Mind:Set Technologies has developed an new customized masking strategy called Harmonic Sound Therapy.  It is specifically designed to deliver targeted acoustic energy to the LPZ/LEF, yet at the same time allow significant portions of the hearing spectrum to remain unmasked.  This design, along with our use of AirDrives headphones, makes it possible to have dramatically increased exposure to the therapeutic sound because the ambient acoustic space is left open.

Harmonic Sound Therapy is designed to exploit the neuroanatomical organization of the “pitch cortex”.   Importantly, when patients are being tested to identify their tinnitus tone, they often mistake their true tinnitus tone for the tone an octave below.  This phenomenon is called “octave confusion”.  The reason why people do this can be explained by the organization of the “pitch cortex”.   

In Western musicology, there are 12 distinct notes that are defined before the pattern repeats itself.  Interestingly, in different cultures, there are a different number of “defined keys”, but the octave relationship is constant.  It turns out that the brain is also organized this way.  There is a special part of the brain that processes pitch which we will call the “pitch cortex” and it is organized like a helix.  (Figure 4)

The essence of Harmonic Sound Therapy is to use stimulation of the LEF and its sub-octave tones (i.e. tones that are in octave intervals lower than the tinnitus frequency) to decrease hyperactivity in the LPZ via the “pitch cortex”.  (Figure 5)

We stimulate sub-harmonic tones to the tinnitus frequency (i.e. the LEF) that avoids the noxious quality that would result if we stimulated the tinnitus frequency alone. 

At Mind:Set Technologies, we have used extensive patient testing to find the combination of sub-harmonic tones that lead to a masking sound that is on the one hand the most comfortable to listen to, and at the same time gives the most therapeutic benefit.  Now in reality, this is not a “tone” per se, but a band of structured noise that surrounds the tinnitus frequency and its sub-harmonics.  Each Harmonic Sound File will be different for each person. 

Our on-line protocol takes into account the tinnitus frequency, the right-left balance, and the difference in hearing from low to high tones to create a customized Harmonic Masking File for each user.  The end result is a file that sounds much like running water in the background, but the result is rather amazing.  Those who use these customized masking sounds feel as if the file “brings their head into balance”, almost as if they are not listening to anything at all. 

 

Because Harmonic Masking only targets the regions of the hearing spectrum that involve the tinnitus frequency and its sub-harmonics, the remaining portions of the hearing spectrum are allowed to pass through to the ear.  This is revolutionary, because it enables people to use their therapeutic sound files during the course of their everyday activities.  Of course, this pass-through phenomenon would not be possible if it were not for AirDrives Technology.