Functional Magnetic Resonance Imaging of the central auditory system in tinnitus patients and healthy controls.

Tinnitus is the perception of meaningless sound in the absence of an external
or internal acoustic stimulus (Lockwood et al., 1998;Melcher et al., 2000;Henry
et al., 2005;Bauer and Brozoski, 2006). It affects 7 to 19 % of the adult
population and it prevents 1% from leading a normal life (Chung et al.,
1984;Coles, 1984;Davis, 1989;Davis and Rafaie, 2000;Nondahl et al., 2002;Henry
et al., 2005). 80% of tinnitus patients have accompanying observed hearing
loss, induced by aging or by noise (Stouffer and Tyler, 1990; Lockwood et al.,
2002;Nondahl et al., 2002;Eggermont, 2003;Heller, 2003;Schwaber, 2003;Crummer
and Hassan, 2004;Eggermont and Roberts, 2004;Davis and Rafaie, 2000).
Despite the high prevalence and morbidity of tinnitus, the pathophysiology of
the disorder is poorly understood. It is thought that tinnitus is the result of
functional reorganization of auditory neural pathways and tonotopic maps of the
central auditory system following peripheral receptor damage. However, little
is known about the exact neural abnormalities underlying tinnitus. One possible
theory on the neural correlates of tinnitus includes increased spontaneous
discharge rate of neurons in auditory cortex and auditory brainstem, and
increased synchronization of spontaneous activity of several cortical neurons
(Eggermont and Roberts, 2004). The mechanism underlying an increase of
spontaneous discharge rate and synchronization is thought to be reduced
(lateral) inhibition which is the consequence of the decreased output from
damaged cochlear regions. There are only few human imaging studies on tinnitus
and these studies confirmed the correlation of increased activity with the
tinnitus percept (Lockwood et al., 1998; Giraud et al. 1999; Melcher et al.
2000).

The proposed study is designed to investigate the neural substrates of tinnitus
using functional Magnetic Resonance Imaging (fMRI). The study is part of the
diagnostic and research program *Diagnosis and treatment of tinnitus with
emphasis on rehabilitation and plasticity* of the department of
Otorhinolaryngology (ORL) of the University Medical Center Utrecht.

The aim of this study is to compare the activation in the central auditory
system in tinnitus patients with the normal system of healthy controls. The
hypothesis is the presence of abnormally high spontaneous activity in the
auditory cortical areas in tinnitus patients. More specifically, we will
investigate the tonotopic maps of the primary and secondary auditory cortex
since the hyperactivity is likely to occur in the specific frequency band of
the tinnitus sound. For the experimental conditions, we will use acoustic
stimuli consisting of different frequencies to stimulate the different
tonotopic maps.

Observation study using 1 patient group and 2 control groups.

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