Tuesday, March 18, 2008

The Brain and Cochlear Implants

At birth, the brain is basically a blank canvas. It has some major pre-wiring, but most of the work has yet to be done. The primary goal of the newborn brain is to learn how to think. As time goes on, it switches gears into thinking to learn. The vast majority of the neural synaptic connections that are made during a person's lifetime occur during the first year. In the first 3 years or so, the entire structure of the brain is laid out. The foundation is formed. That is when language acquisition occurs. As language is learned, it in turn helps create more of the foundation. Visual language is learned separately from oral language. While the two can support and assist each other, if either is delayed, that language cannot assist in basic brain development.

The auditory center of the brain REQUIRES sound and language in order to develop. And it generally requires the same amount of time as the rest of the brain, about 3 years. The longer sound and verbal language is delayed, the less brain development occurs in the auditory center. For those with mild to moderate hearing loss, a hearing aid is usually adequate in providing that basic verbal language acquisition. For those babies with a severe to profound loss, hearing aids simply cannot supply the needed input in all frequencies. If any frequency is missing, then that area of the auditory center does not develop.

The reason many older kids and adults don't do as well with their cochlear implants as infants and toddlers do, is that they are past the point where the auditory center can do much development. If they had adequate auditory brain development as infants (a progressive loss, good use of hearing aids, etc…) then they will probably do quite well with the implant. If the auditory center did not get full development, then no matter how well the implant works, the brain simply is not capable of making sense of the sound. Thus, it becomes meaningless noise. This is a simplified version, showing two ends of the spectrum. The more developed the auditory center is or can become, the better the implant works.

So while children with a mild to moderate loss, or those who get good results with hearing aids have time on their sides, those with a severe to profound loss that don't respond well to hearing aids do not. For those babies, the clock is ticking, and time is not their friend.


No comments: