Progress toward the development of a
neurovestibular prosthesis
Daniel
M. Merfeld
Abstract:
Disorders of the peripheral vestibular system are relatively common and
often result in severely impaired mobility, blurred vision and
debilitating attacks of vertigo and motion sickness. Presently, little
can be done to resolve these symptoms when they are chronically present.
While data are limited, prevalence of profound vestibular problems appears
about the same as profound hearing loss. Preliminary research in the area
of vestibular neuroprosthetics alongside the success of the cochlear
implant, provides hope that providing motion cues via electrical
stimulation may eventually help some patients suffering severe vestibular
impairment. We have developed and tested a prosthetic device that senses
angular head velocity and uses this information to modulate the rate of
current pulses applied to the vestibular nerve via an electrode. In this
talk, I will present our preliminary findings demonstrating the
feasibility of a vestibular prosthesis.
In three squirrel monkeys, the lateral canals were plugged bilaterally and
our prosthesis was secured to the animal's head with the angular velocity
sensor parallel to the axis of the lateral canals. The stimulating
electrode was placed near the ampullary nerve of one lateral canal. When
rotated in the dark, the animals responded with an appropriate
vestibulo-ocular reflex (VOR), which adapted over time, providing evidence
that the CNS was utilizing the information provided electrically. In
another experiment, a guinea pig was provided chronic constant-rate
stimulation and responded with a brisk nystagmus that adapted away after
about a day. When the stimulation was removed, a brisk nystagmus in the
opposite direction was measured, again lasting about a day. These
findings demonstrate adaptation to the constant rate stimulation. When
the stimulation was alternately turned on and off weekly, the nystagmus
response began to decay more rapidly, eventually decaying just a few
seconds after the device was turned on or off. This indicates that with
repetitive application of chronic stimulation, the animal learned to adapt
rapidly to the present state (on or off) of stimulation. Such "switching"
will be important for users of vestibular prosthetics so they don't feel
disoriented when they remove the device to sleep, shower, etc. While
preliminary work suggests clinical potential, many technical challenges
must be addressed prior to clinical use.
Recommended readings:
1. Wall C, 3rd, Merfeld DM, Rauch SD, Black FO (2002) Vestibular
prostheses: the engineering and biomedical issues. J Vestib Res 12:95-113.
2. Lewis RF, Gong W, Ramsey M, Minor L, Boyle R, Merfeld DM (2002)
Vestibular adaptation studied with a prosthetic semicircular canal. J
Vestib Res 12:87-94.
3. Gong W, Merfeld D (2002) System design and performance of a unilateral
semicircular canal prosthesis. IEEE Transactions on Biomedical Engineering
49:175-181.
4. Gong W, Merfeld D (2000) A prototype neural semicircular canal
prosthesis using patterned electrical stimulation. Annals of Biomedical
Engineering 28:572-581.