Tinnitus and hearing loss are intimately related. Hearing loss may be the main cause of a person’s tinnitus while tinnitus can diminish a person’s ability to hear. Since the two go hand in hand, it is important to understand their relationship and how each impacts the management and treatment of the other.
If a tree fell in the woods…
If a tree fell in the woods and no one was there to hear it, would it make a sound? This ancient, perplexing question actually has a straightforward answer: no. Sounds are only sounds because of the biological structures that process them. Until a “sound” reaches the ear it is only a pressure wave or disturbance. The wave strikes the eardrum, which moves three small bones in the middle ear, which in turn move fluid within the cochlea. Depending on the frequency of the pressure wave, hair cells within the cochlea are disturbed emitting electrical signals to the brain. The brain processes these electrical signals as sounds. The brain assigns them a quality and a meaning. Without a functioning auditory system, there would be no sound, only pressure waves.
When hearing is lost
Why the philosophical and scientific discussion? It helps to frame a discussion of hearing loss. As alluded to above, the auditory system is complex. As a complex system, there are a number of ways in which it can go awry. When the auditory system does go awry, it can lead to decreased hearing or deafness (It can also cause tinnitus, as we will see). Something as simple and treatable as impacted earwax in an ear canal can cause deafness. A punctured (perforated) eardrum prevents pressure waves from being converted to mechanical energy. Abnormal bone growth or infection can keep the tiny bones in the middle ear from moving smoothly. If they cannot move, the bones cannot transmit the movements of the eardrum. Loud noises and certain drugs can damage and destroy the cochlea, more specifically the hair cells contained within. A number of neurological problems can disrupt the nerves involved in hearing—all leading to some degree of deafness.
The brain needs input
The brain works best when it gets constant input. When one has lost hearing, the input from the nerves that carry information about sound are no longer providing the brain with as much input as it would like. When the brain is deprived of electrical input from nerves, like auditory nerves, strange things happen.
To help illustrate the point, consider someone that has suffered the loss of an arm. When the nerves to the arm are severed, the nerves wither and die, all the way up to the brain. Obviously these nerves no longer provide input to the brain about heat, pain, or touch. Some amputees suffer a curious disorder called phantom limb syndrome in which the person feels pain, burning, or other sensations in the lost limb. This is not a pain in the stump that remains—this is pain in the portion of the limb that is no longer there.
Hearing loss and tinnitus
While it is not a perfect analogy, tinnitus that is associated with hearing loss is roughly similar to phantom limb syndrome in a lost limb. When the input from the cochlea to the brain is diminished, tinnitus may be caused by abnormal electrical activity that is generated in its place. The abnormal electrical activity in tinnitus and hearing loss is thought to be twofold. One, nerves coming from the cochlea are actually hyperactive, though not necessarily corresponding to sound input coming from the world. Instead of “hearing” distinct sounds, these nerves create the sensation of strange sounds like ringing, humming, or buzzing. Two, the area of the brain that is responsible for hearing, the auditory cortex, gets bigger (in a manner of speaking). More cortex devoted to lost nerves makes for some strange noises (consistent with tinnitus).
These neurological changes actually create a paradox, of sorts. A large portion of patients suffering from tinnitus also suffer because of hyperacusis. Hyperacusis is a condition in which sounds over a certain frequency are overly loud and even painful.When you consider the changes that occur in hearing loss and tinnitus, it is not difficult to imagine how hyperacusis is related as well. If hearing loss leads to aberrant neuronal input to the brain, even soft sounds are sent the auditory cortex in a massive assault, which the brain registers as a loud (or painfully loud) sound.
The solution to hearing loss, hyperacusis, and tinnitus might rest in Tinnitus Retraining Therapy and related treatments. Tinnitus Retraining Therapy seeks to retrain the auditory system to process sounds normally and undo the abnormal connections in the brain. Some Tinnitus Retraining Therapy devices use a hearing aid along with a noise generator to help improve a patient’s ability to hear but also to minimize tinnitus. The white noise generated in Tinnitus Retraining Therapy tends to cause the brain to “habituate” or get used to the tinnitus sound. When hyperacusis is one of the symptoms, the noise therapy is sometimes hindered by the volume that can be used. However if an audible, but not painful sound can be used to retrain the auditory system, it can correct both tinnitus and hyperacusis.
Taking the idea of stimulation one step further is research into cochlear implants. Cochlear implants are devices that convert sound waves entering the ear into electrical impulses that are sent to the brain. Cochlear implants have been pioneered for use in patients with congenital or acquired deafness, but the principle of how they work seems to lend itself to the treatment of tinnitus as well.
One treatment that has been tried for decades is electrical stimulation of the ear. By providing electrical stimulation of the cochlea, the auditory cortex is almost directly stimulated. This gives the brain the input it craves, but could also overwhelm the neuronal pathways that underlie the tinnitus sound. Both are helpful.
As it stands right now, a cochlear implant is not a primary treatment for tinnitus. The devices are quite expensive and are not indicated as sole treatment of tinnitus. However, in patients that are candidates for cochlear implants because of hearing loss and also have tinnitus, the implanted devices may provide a cure for both conditions.