Functional MR Studies of vestibular and visual interaction

Interaction between the vestibular and visual systems can be simulated by
providing caloric vestibular stimulation. When the subject*s eyes are closed,
this induces a strong sense of rotation. But when the subject*s eyes are open,
a mismatch is created between the vestibular system (sense of rotation) and the
visual system (sense of stability). When cold water is used to provide the
stimulation, slow phase eye movements (i.e., nystagmus) are resulted towards
the side on which the stimulus is given and hence induced a perception of
rotation rotating away (around the vertical body axis) from that side.
However, when warm water is used, the slow phase eye movements are moving away
from the side on which the stimulus is given and hence induced a perception of
rotation rotating (around the vertical body axis) from that side .

Current approaches to study human brain activation of vestibular stimulation
use of blood-flow measurement with Single Photon Emission Computed Tomography
(SPECT), functional Magnetic Resonance Imaging (fMRI) and Positron Emission
Tomography (PET). These imaging studies of caloric vestibular response in
humans have combined unilateral stimulation or bilateral stimulation with the
combination of gas, cold water or hot water as the stimulant. These studies
have always been done with the subjects* eyes closed. Up to now, however, a
few comparisons have been made between unilateral and bilateral stimulations
and between eyes-closed and eyes-open conditions.

In this study we used fMRI to measure the blood oxygenated level dependent
(BOLD) response during caloric vestibular stimulation. We setout to
investigate the involvement of the cortical and sub-cortical brain areas during
visual-vestibular interaction and compare the difference between the eyes
closed and eyes open conditions with unilateral or bilateral stimulation with
cold and warm water.

Primary Objective: To investigate the involvement of the cortical and
sub-cortical brain areas during visual-vestibular interaction and

Secondary Objective: To compare the difference between the eyes closed and eyes
open conditions with unilateral or bilateral stimulation with cold and warm
water.

A volunter will be scanned twice for one hour. During the scansession cold or
warm water will be injected in one or both ears.

In this study we used fMRI to measure the blood oxygenated level dependent
(BOLD) response during caloric vestibular stimulation. fMRI is a
non-invasive imaging technique. Brain activity in fMRI is based on the
observation that increased neural activity leads to an increase in localized
cerebral blood flow, blood volume, and blood oxygenation.

Each fMRI study and for each volunteer has 2 experiments and will last for 1
hour each.
During the experiment warm or cold water will be injected into the ear of the
volunteer and this would induce a sensation of rotation to the volunteer. The
sensation will only last for a minute or two.