Causes of Subjective Tinnitus

The “source” of most subjective tinnitus is not known. It is easy to attribute the responsibility to the hair cells, saying that they malfunction and instead of detecting sound they operate abnormally producing electrical signals which are then perceived as sound. This is difficult to prove scientifically, and although this must be true for some patients, it cannot be used as a general explanation.

However, there are some specific causes of subjective tinnitus that need to be excluded. This is applicable especially in tinnitus found in one ear, where, among other causes, diseases of the middle ear and the mastoid antrum should be excluded. The investigation includes physical examination and imaging techniques such as computed tomography or magnetic resonance imaging.

Tinnitus in one ear accompanied by hearing disorder is caused in some cases of acoustic neuroma. This is most likely when there is sensorineural hearing loss on the same side. The ideal way to discover if the patient has these annoying but benign tumors is to refer the patient for an MRI. This review provides enough information to confirm that the patient has a tumor or other disease in the head, in which case the tinnitus is called “idiopathic”, which practically means without yet known etiology.

As technology improves and our understanding of the mechanisms of tinnitus increases, the group of idiopathic tinnitus, which consists of the majority, will be less, since specific causes of the problem will be found. Each time a clear justification will be determined, specific treatment regimens will be available.

However, at present for people with idiopathic tinnitus without hearing loss, the only thing we can say is that in a post route from the cochlea to the auditory cortex abnormal electrical signals are caused. For patients with hearing loss and tinnitus alternative mechanisms to explain the tinnitus have been proposed: From the hair cells in the cochlea and inwards, the hearing system is a network of electric fuses, connectors, reinforcing devices, filters, etc. Each electrical system has within it the so-called “electrical noise”. This is easily demonstrated using a Hi-Fi amplifier that is turned to maximum volume without having installed a CD or cassette to play, so even if the system is too expensive, you will hear some noise through the speakers.

There will always be a background electrical noise in the system of hearing, but normally you cannot hear it because your brain sets a threshold level that causes it. That is, to hear a sound signal it should be above the threshold of background sounds. People have a wide range of hearing thresholds.

When hearing loss occurs, regardless of etiology, it may be enough to prevent normal external sounds to reach the brain. The “silence” in a frequency scale recognized as hearing loss is certified by the brain. Our world is not silent (it may be quiet, but silence is extremely difficult to achieve) and the absence of sound means that our first warning system fails to record changes. Therefore, the brain reacts by lowering the threshold to “listen” more and by doing so it enters the levels of internal sounds, and thus the person also hears the functions of their own ear.

Most people with normal hearing, if placed in a perfectly silent room (soundless chamber) for experimental reasons, will develop tinnitus, which disappears when they return to a normal noisy environment. The phenomenon occurs every time the experiment is repeated, but most people do not like the feeling of absolute silence because it causes them a feeling of fear and discomfort. This probably happens because they now do not have hearing as an early warning system and they feel vulnerable at the brainstem of primitive animals.