Magnet implants – to (re)gain a fifth sense

Did you know that the main reason for hearing problems and deafness is hair loss? And that magnets can be part of the rescue?

Following last week’s post on magnet implants, I will now show you an example where magnet implants are truly functional, and are already in use: cochlear implants, advanced hearing aids.

Cochlea is the fancy name for the inner ear. As you know sound waves enter the ear through the outer ear, goes through the ear canal and reaches middle ear where the eardrum, hammer, anvil and the stirrup starts vibrating in a chain. The vibrations reach the inner ear, the cochlea, where the mechanical energy is converted into electrical signals that nerv cells can transport to the brain so that we can make sense of the sounds.

So, I mentioned that hair loss can lead to hearing problems?

The cochlea is a spiralling tube that is filled with fluid and lined with sensory cells, aka ‘hair cells’, through the whole tube. The hair cells have varying sensitivity to sound frequencies; high pitch tones are absorbed in the base of the spirall, and base tones further in, in the apex. When the vibrations from a sound enters the cochlea, the liquid starts moving, and the surface of the hair cell moves correspondingly. These movements creates tension differences which produce electrical signals that are passed along the hearing nerve to the brain.

It’s all very nicely animated in this video by Med-El (from which the description above is taken):

Screen Shot 2015-06-10 at 11.12.41

Hearing problems can be due to defects and damages in either the outer, middle, or inner ear. Most are related to the inner ear, and the lack of, or damaged, hair cells in the cochlea!

Damaged hair cells can cause distorted hearing, tinnitus, and deafness. It is also the reason why humans get worse hearing when growing old, becausethe hair cells can get damaged by noise, drugs, infections etc, and they can’t regrow.

Under an electron microscope, it can look like this:

heatlthyAndDamagedHairCells-1.jpg

image source: wi-cancer.info

Luckily, there is help to be found: the cochlear implant. Unlike the ear, there are only two parts of it, the external and the internal. The external part consists of a microphone that picks up sound, and a speech processor that digitizes the sound into signals which are then transmitted into the (internal) cochlear implant by a transmitting coil. On the inside, in the actual implant, there is an internal processor placed behind the ear (fixed in a bone), that picks up the message and sends electrical energy to an array of up to 22 electrodes that has been inserted into the cochlea and replaced the hair cells in the job of stimulating the auditory nerve fibers in there.

CIdiagram_MAESTRO Cross Section_720

Image source: cochlear-implant.co.uk

The surgery takes a couple of hours and the patient can normally go home on the same day. After 1–4 weeks of healing, the implant is “activated” by connecting the external part to the internal device, via magnets on each sides! (shown more clear below)

Print

Image source: nyee.edu

The initial results of the implant vary widely, and post-implantation therapy is required as well as time for the brain to adapt to hearing new sounds.

Hearing with the implant is not exactly like normal hearing; voices can sound static, robotic or cartoonish. You can try it out on this site.

Remember, 22 electrodes have been given the task to replace 16000 hair cells which is quite a challenge, so there are ideas to increase the number of electrodes. Most patients only get the implant on one ear, but studys suggest that it might help to get one on the second ear as well. This would give stereo hearing and help in sound localisation, and it might even make music appreciable.

The implant is only for people with severe hearing problems, or that are deaf. It is for adults who have been able to hear before, and learnt how to process sounds, or for children who have not passed the critical time where humans learn this, so preferably before the age of 2-3. (Kids who lack an auditory nerve can get auditory brainstem implant, which is similar but the signal goes straight to the brainstem instead of the cochlea.)

The implant is quite expensive so it is more frequent in richer countries. The cost for the implant should however be related to what is saved on special-education costs that are no longer needed. In 2000 it was stated that 1/10 children born deaf in the US had cochlear implants, and the number was expected to grow fast.

Hopefully it will, because:

Seeing the reaction of someone regaining their sense of hearing is truly something.
Or an infant that hear it’s parents’ voices for the first time.

 

Read more:

http://en.wikipedia.org/wiki/Cochlear_implant

http://www.cochlear.com/wps/wcm/connect/sv/home/understand/hearing-and-hl/hl-treatments/cochlear-implant

http://www.nidcd.nih.gov/health/hearing/pages/coch.aspx

 

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