Hearing implant knows where it goes.

Engineers out to improve the performance of cochlear implants have developed a version with sensors that may aid a surgeon in installing the device optimally.

Cochlear implants can restore hearing to people with deafness caused by damage to vibration-sensing cells (SN: 12/10/05, p. 371). The devices translate sounds into electric signals that travel to a narrow probe covered with electrodes. That probe, inserted into the coiled inner ear tube known as the cochlea, directly stimulates auditory nerve fibers.

When installing any cochlear implant, a surgeon threads its electrode-studded probe into the cochlea's inward-spiraling interior. The farther in that the electrodes go, the wider the range of frequencies that the listener can detect--and the better he or she will hear, says Kensall D. Wise of the University of Michigan in Ann Arbor. However, surgeons typically insert the probes so cautiously that the electrodes don't reach optimal depths.

A prototype implant developed by Wise and his Michigan colleagues Mayurachat Gulari and Jianbai Wang includes piezoelectric sensors in the probe. These sensors generate electrical signals in response to mechanical forces. The unusual micro-fabricated implant is also exceptionally slim and packs more electrodes onto its surface than conventional implants do.

A sensor at the tip of the probe responds when it bumps the cochlear wall, so surgeons can make adjustments during insertion, Wise says. Signals from sensors along the probe indicate how coiled it has become and so reveal how far into the cochlea it has penetrated, he adds. A surgeon could therefore guide a probe deep into the cochlea while minimizing destructive contact with the channel's walls, says Wise.

Wang discussed the new implants, which are currently being tested in animals, at the IEEE International Electron Devices meeting last month in Washington, D.C.--P.W.