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Low-power chip keeps cochlear implants out of sight

Posting in Healthcare
  
Hundreds of thousands of people around the world depend on cochlear implants to hear. However, existing versions of these types of implants -- which electrically stimulate the auditory nerve -- require a skull-mounted sensor. A disk-shaped transmitter (about an inch in diameter) is affixed to the skull, and a wire extends down to a microphone and power source, which look like a large hearing aid around the ear.

Now, MIT researchers have developed a low-power signal-processing chip, which could lead to a cochlear implant that doesn’t require any exterior hardware. 

Rather than use an external microphone to gather sound, the new implant would use the natural microphone of the middle ear. Okay, a quick anatomy lesson, from the MIT News Office

Delicate bones in the middle ear, known as ossicles, convey the vibrations of the eardrum to the cochlea, the small, spiral chamber in the inner ear that converts acoustic signals to electrical. In patients with middle-ear implants, the cochlea is functional, but one of the ossicles -- the stapes -- doesn’t vibrate with enough force to stimulate the auditory nerve. 
cochlea from Grays Anatomy.png
A middle-ear implant uses a tiny sensor to detect vibrations of the ossicles and an actuator to drive the stapes accordingly. The new cochlear implant would use the same type of sensor, but the signal generated travels to a microchip implanted in the ear -- which then converts it to an electrical signal, passing it on to an electrode in the cochlea. 

To do away with the skull-mounted hardware, the team had to lower the power requirements of the converter chip. MIT News explains

The key was to specify a new waveform -- the basic electrical signal emitted by the chip, which is modulated to encode acoustic information -- that is more power-efficient to generate but still stimulates the auditory nerve in the appropriate way.

The implant would be wirelessly recharged and could run for about eight hours on each charge. The researchers also have a prototype charger that plugs into a cellphone and can recharge the chip in two minutes.“The idea with this design is that you could use a phone, with an adaptor, to charge the cochlear implant, so you don’t have to be plugged in,” says study coauthor Anantha Chandrakasan of MIT. “Or you could imagine a smart pillow, so you charge overnight, and the next day, it just functions.”

The work was presented at the International Solid-State Circuits Conference this week. 


Image: cochlea from Gray’s Anatomy via Wikimedia

— By on February 13, 2014, 9:13 PM PST

Janet Fang

Contributing Editor

Janet Fang has written for Nature, Discover and the Point Reyes Light. She is currently a lab technician at Lamont-Doherty Earth Observatory. She holds degrees from the University of California, Berkeley and Columbia University. She is based in New York. Follow her on Twitter. Disclosure