Chances are you or someone you know suffers from tinnitus, a phantom sound described as a continuous ringing, buzzing or whistling. This sound is perceived within the ears or the head that occurs without any external source of sound. However, it is not the ear that is responsible for tinnitus though it may be one factor. Instead, the cause of a person’s tinnitus can be found in the brain. Normally, hearing sounds of any kind only occur when sound waves enter the ear canal. Vibrate the eardrum which moves the middle ear bones. Stimulating the cochlea which finally triggers a nerve signal that goes to the brain. Sound information in the brain is processed in a very specific brain area known as the auditory cortex. The auditory cortex is divided up into areas that are responsible for processing different pitches in a similar way to keys on a piano. Under normal circumstances, there is always a baseline of on-going neural activity. When sound is present, however, the neural activity increases above baseline. When there are no sounds present, this activity is at a baseline that establishes your neural code for silence. Anything which causes us to lose our hearing can disrupt this internal keyboard. This disruption could be caused by medication, loud noises, or just getting older. With fewer cochlear cells relaying information, incoming sounds generate weaker nerve signals. To compensate, the brain devotes more energy to monitoring the hearing pathway. Just like one might adjust the knobs of an old analog TV or radio if it is hard to hear music, the brain modifies neural activity while also tweaking the tuning knob to get a clearer signal. Increasing this background neural activity is intended to help process weak auditory inputs but it can also modify the baseline for silence such that a lack of sound no longer sounds silent at all. Similarly, turning the volume knob of a TV or radio way up where silence ideally should be present, a constant hiss from the speaker will be heard instead.
Ultimately, with reduction of neural activity in the keyboard areas of the auditory cortex affected by hearing loss, the nerves that make up the area can start to fire spontaneously in an overactive and unregulated way. This is called neural synchronization.This abnormal overactivity is what causes the perception of tinnitus. Just like phantom limb pain may occur after an arm or leg amputation, think of tinnitus as a phantom sound after a sound amputation. Over time, this abnormal activity becomes permanent. This abnormal neural synchrony does not remain limited to the auditory center. Brain areas regulating attention, emotions and stress are also affected. The faulty signals in all these areas together causes a psychological loop that allow the tinnitus tone to invade into our consciousness and influence the individual level of stress and anxiety experienced by each person as well as the perceived volume and invasiveness of the tinnitus. Treatment is geared towards addressing some or all of these factors depending on test results and how bothersome the tinnitus is. Hearing aids can boost the auditory signal if significant hearing loss is present. Acoustic neuromodulators can potentially reduce and reverse the neural synchrony. Sound therapy uses noises like rain, birdsong, or ocean waves to mask tinnitus and reduce stress. Diet changes like eliminating salt intake can also improve tinnitus as well. If there is a large component of stress and anxiety associated with tinnitus, a vicious circle among these components can occur leading to significant psychological distress. Medications typically used to treat anxiety often cause tinnitus as a side effect. As such, counseling interventions like tinnitus retraining therapy are used to break this tinnitus cycle. Other interventions like cognitive behavioral therapy allow people to re-evaluate their relationship with tinnitus in order to decouple the sound association with anxiety and stress without the need for medications.