Tinnitus. An MRI study on brain mechanisms

PhD ceremony: Ms. K. Boyen, 12.45 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: Tinnitus. An MRI study on brain mechanisms

Promotor(s): prof. P. van Dijk

Faculty: Medical Sciences

Tinnitus, or ‘ringing in the ears’, is the percept of a sound that is only heard by the patient. It is often associated with hearing loss. In this thesis, a number of studies investigated the human brain in tinnitus patients by means of structural and functional Magnetic Resonance Imaging (MRI).

A voxel-based morphometry approach was used to compare gray matter in a hearing-impaired group of subjects suffering from tinnitus to a hearing-impaired control group. Tinnitus was associated with gray matter increases in the left primary auditory cortex and several areas belonging to the limbic lobe. Comparing the same groups revealed that tinnitus is accompanied by a significantly decreased functional correlation between the auditory cortex and inferior colliculus as compared to the hearing-impaired controls. Many patients are able to modulate their tinnitus by both movements and pressure applied to the head, neck and face. The results of previous brain imaging studies show that modulated tinnitus corresponds to an increased level of activity throughout the central auditory system. We explored the relation between the loudness of modulated tinnitus due to eye movements and brain activity. An increase in loudness corresponded to an increase of activity in the auditory cortex, inferior colliculus and cochlear nucleus, but not in the medial geniculate body. Both the latter result as the weaker functional connection may be interpreted as an abnormal functioning of the thalamus in tinnitus patients.