Audiometric evaluation of tinnitus inhibition by cochlear implant stimulation.

Subjective tinnitus is the perception of sounds in the absence of a physical
sound source. It can only be perceived by the patient himself. The prevalence
of tinnitus is 4.4% -20% in the general population and 66-100% in the
population of cochlear implant candidates. A key hypothesis in the pathogenesis
of subjective tinnitus is that it arises as a response of the central auditory
system to peripheral hearing loss. Peripheral hearing loss results in a
decrease of afferent input to the brainstem. This may result in an increase of
spontaneous neural activity at several levels in the auditory brainstem and
cortex, which is believed to potentially cause tinnitus. Several authors
described the positive effect of electrical stimulation of the ear on tinnitus,
with success rates ranging from 4-87%.The first report of subjective tinnitus
being suppressed by electric stimulation through a cochlear implant was in
1976. After that several researchers have confirmed these results, showing that
suppression of tinnitus occurs in 40-86% of the cochlear implant recipients.
The mechanism by which electrical stimulation reduces tinnitus is still
unclear. Increase in neural activity (masking) seem to play an important part,
but also some (central) nervous system effect seems to play a part in the
influence of electric stimulation on tinnitus suppression. In this study we
will investigate the influence of various kinds of electrical stimulation by
cochlear implants on tinnitus. These experiments may identify stimulus
strategies that are potentially successful as a treatment of chronic tinnitus.

To evaluate the efficacy of various masking strategies in cochlear implants as
a treatment for tinnitus in patients with profound hearing loss.

parametric exploratory study

A listening experiment will be performed. It consists of several runs. In each
run, the subject listens to a stimulus for a certain amount of time. He records
the loudness of the stimulus and the loudness of the tinnitus on a scale from 0
to 10 (with 0 being very weak and 10 being very strong), once every 15 seconds.
This recording starts 1 minute prior to the stimulus onset, and last until the
tinnitus has come to its original loudness after the end of the stimulus. The
electrical stimuli will differ in: pulse rate, stimulation electrode,
amplitude, and duration.

It is expected that patients will not experience disadvantage of this
experiment. The burden that is additional to standard care is the time and
effort that patients have to put in this experiment. Patients have to come to
the hospital for an additional visit. The listening experiment is done once in
each patient and will take approximately 120 minutes, including frequent
breaks.