Functional Connectivity in the Central Auditory System; Optimization of the Acoustic Environment

In the last decade is has become possible to study the functioning of the
central auditory system in the human brain by means of functional MRI (fMRI).
Using this method, the brain activity that occurs in response to a presented
stimulus can be mapped. However, conventional stimulus-related fMRI experiments
are hardly applicable in some cases, for example when the subject's sound
perception cannot be controlled properly. This is for instance the case in
tinnitus patients that perceive unremitting sounds in the absence of any
external sound sources ('ringing in the ears').
Recently, methodologic studies have appeared describing new fMRI methods that
are not aimed at determining activation in brain areas, but that focus on
connectivity between brain areas. Due to this difference, such methods depend
less upon well-defined stimulus conditions, which may make them very
appropriate to study the aforementioned tinnitus patients.
When investigating the central auditory system using fMRI, specific problems
arise because of the presence of scanner noise. During measurements,
MR-scanners produce very intense acoustic noise, which is perceived by the
subject and thus interferes with the neural activity in the auditory brain
areas. For conventional fMRI-setups, practical measures exist to minimize the
influence of this noise. However, it is yet unknown whether these measures are
equally suitable in the context of new connectivity related fMRI methods.

The objective of this study is to determine the influence of ambient noises
upon the characteristics of fMRI signals that are of relevance in connectivity
measurements.
The study will focus on the influence on the statistical properties of
measurable fMRI signals of scanner noise in particular. Additionally, the
effectiveness of so-called sparse acquisition paradigms will be compared to
that of continuous paradigms (sparse paradigms are common in conventional fMRI
setups to limit the influence of scanner noise). Finally, it will be studied
whether it is advantageous to excite the central auditory system by means of
sound presentations on behalf of determining connectivity parameters.

After inclusion, the subject will undergo a clinical hearing test to verify
that their hearing is normal. Hereafter, subject will participate in an fMRI
session. Apart from a number of orienting anatomical scans, this will consist
of series of functional acquisitions that are capable of detecting brain
activation and connectivity. These series will comprise blocks of sparse and
continuous acquisitions, that will be randomly alternated. In addition, sound
fragments will be presented during some blocks, while no sound will be audible
in other blocks (except for the scanner noise). The subjects are instructed to
memorize the sound fragments during the blocks with sound presentation. In a
task that is performed immediately after the fMRI session, a series of sound
fragments will be presented in which the subject is asked to indicate whether
these are familiar from the previous fMRI session or not.
To assess the reproducibility of the measurements, half of the subjects will be
requested to participate in an identical fMRI session on a later day.

The burden will consist of participation in a hearing test of approx. 10
minutes, followed by an fMRI session and sound recognition task of 2 hours
(taken together). Half the subjects will participate a second time in an
identical fMRI session and sound recognition task.
Risks are naught.