Rutgers Discovery Offer Potential for Improved Cochlear Implants
Editor: Scientists at Rutgers are unraveling the mysteries of some
proteins that work their magic deep within the cochlea, and what they're
finding offers promise for improved hearing technology, including cochlear
implants!
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A Rutgers University team led by neuroscientist Robin Davis is opening
new doors to improved hearing for the congenitally or profoundly deaf.
Their findings could lead to a new generation of cochlear implants.
Cochlear implants today operate with varying degrees of success in
different patients. Some may be able to hear sounds like the rush of
traffic or the crash of thunder. Others can do even better, detecting
voice and understanding speech while still being unable to appreciate
music. With the latest research, across-the-board improvement may be
within reach.
Davis' work is important for engineers and surgeons in designing new
cochlear implants. "The significance of our work lies in the fact that we
can change an element in a very peripheral part of the sensory system that
can have an impact all the way into the brain," Davis said.
Cochlear implants, also known as "bionic ears," are surgically inserted
into the snail-shell shaped structure - the cochlea - within the inner
ear. Ordinarily, hair cells line the cochlea and convert acoustic signals
into electrical signals that nerves then carry to the brain. Where some
hair cells exist, sounds can be amplified with a hearing aid. Where the
hair cells are missing or damaged - a condition generally associated with
severe hearing impairment - an implant may be used to replace their
function.
Davis, a professor in the Department of Cell Biology and Neuroscience
of Rutgers' School of Arts and Sciences, works with mouse cochlear tissue
cultured in the laboratory. The spiraled cochlea is unwound and laid out
in a line. Davis described the hair cells as being analogous to the keys
of a piano and the nerves to which they attach - the spiral ganglion
neurons that connect to the brain - are the piano's strings.
"Our studies have revealed that spiral ganglion auditory neurons
possess a rich complexity that is only now beginning to be understood,"
said Davis.
The researchers found that two neurotrophin proteins in the cochlea -
brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) -
figure prominently in the relay of sound messages to the brain. Research
by Davis and her team, begun more than six years ago, is now producing
insights into precisely how these multidimensional proteins operate in the
cochlea. These most recent findings appear in the Dec. 19 issue of The
Journal of Neuroscience.
While neurotrophins have historically been prized for the survival
value they impart to nerve cells, the researchers found that in the
cochlea they do a great deal more. Their presence in relative proportions
transforms the spiral ganglion neurons into either fast-firing
transmitters to carry high pitched sound messages to the brain, or
slow-firing carriers for the transmission of lower pitched signals. The
neurotrophins accomplish this at the molecular level by tightly regulating
a newly-defined and complex series of signaling proteins.
Davis explained that one end of the cochlea is home to the
slower-firing neurons characterized by a preponderance of NT-3, while the
other cochlear end is rich in BDNF, making those neurons faster-firing.
Both neurotrophins are present in gradients throughout the range, but at
any specific locale their amounts vary relative to each other - lots of
BDNF and a little NT-3 in the high frequency transmitters, for example,
and the reverse as you move toward the other end.
In one possible remedial approach, Davis described how the
neurotrophins could potentially be pumped into a newly-designed cochlear
implant and released through graduated ports along its length.
