Around 15% of the population suffers from tinnitus. This sensation of hearing a buzzing, ringing, swishing or clicking noise in one or both of the ears although no other sound is emanating from the immediate environment has recently been studied by a team of researchers from the Cyclotron Research Centre of the University of Liège and the ENT department of the University Hospital of Liège. The study looks at the problem from the perspective of functional magnetic resonance imaging and has been published in PLoS ONE.

Among those who suffer from tinnitus (around 15% of the population), only 10 to 20 percent suffer from it to the point that it alters their quality of life. In this case, tinnitus can leave a comorbidity in its wake in the form of irritability, (and therefore tiredness), concentration problems and depression. “Tinnitus is sometimes very difficult to live with and has already led to suicide”, indicates Professor Philippe Lefèbvre, head of the Ear Nose and Throat Department of the University Hospital of Liège.  “Certainly, in the case of a patient suffering from depression, it is sometimes mooted as the cause of the depression, while the problem may be much deeper”

Tinnitus is mostly accompanied by noises of 10 to thirty decibels. However, much more exceptionally, these noises can be equivalent to about 70 or 80 decibels – a normal conversation is at about 55 decibels. In those who do not feel handicapped by their tinnitus a phenomenon called habituation comes into play: the brain filters the parasitical information to the extent that the “phantom noises” are banished to the subconscious. As Professor Lefebvre points out, it is the same mechanism which prevents us from focusing our attention on the ticking of a clock or the rubbing of our clothes against the body.

Subjective evaluation  

In fact there are two types of tinnitus. Described as “objective”, the first are in the minority (perhaps 5% of cases). With the aid of his stethoscope, a doctor can hear them. They are generally the result of a vascular deformation (for example, a blowing noise can be heard around the carotid) and for this reason are of the pulsatile kind as they are synchronized with the beating of the heart, or call to mind the idea of swishing, (blood flow). “To get rid of this kind of tinnitus, the underlying problem must be dealt with- for example, by treating the shrinking of the carotid artery”, explains Philippe Lefèbvre.

Most cases of tinnitus are “subjective” therefore. Linked to a malfunctioning of the auditory pathway, they are only experienced by the individual suffering from them. They are grouped into two main categories. The first includes tinnitus caused by an increase in the frequency of potential action discharges in the cochlea (ciliated cells, neurons). Put another way, the ear starts to send signals which do not respond to any external stimulus. The second category consists of tinnitus whose primary cause is a deterioration of hearing acuity, particularly with age. What is actually happening? The deterioration in the function of the auditory pathway is accompanied by a reduction of inhibitions in the cerebral cortex. At least that is the most likely hypothesis. This suggests that the brain attempts to compensate for the loss of hearing by increasing its activity and this generates “phantom sounds”.