Many hearing aids work by simply amplifying incoming sound and relaying it into the ears of the person hard of hearing. For those with more severe hearing loss, such a device is not always sufficient. A cochlear implant can be a solution (although many deaf people don’t feel the need). It completely skips the damaged parts of the ear by recording sounds from the environment then transmitting them directly to the auditory nerve.
On the receiving end of this artificial signal is the deaf person’s auditory cortex, a part of the brain that is no longer accustomed to receiving this kind of input – instead, visual areas will have recruited the regions normally employed in auditory processing. As a result, a deaf person’s visual processing is better than average and they have enhanced visual attention, which is essential in sign language. The underlying mechanism is neuroplasticity and is the characteristic that enables the brain to be the incredibly adaptive organ it is. Thanks to neuroplasticity, blind people can use echolocation for spatial awareness, and limb amputees will be able to control their prosthesis with their brain.
In a new study, a group of French and Swiss researchers described the role of such neuroplasticity in the speed a deaf person’s brain can adapt to the installation of a cochlear implant. They measured brain activity and speech comprehension right after the operation, and again six months later and found, predictably, that increased activity in targets brain regions correlated to an increase in patients’ speech comprehension scores. Interestingly, they also found that patients whose visual processing areas were more active at the start showed better speech comprehension recovery than other patients.
Before the patients in the study received their cochlear implants, they relied more on visual input for the processing of language than hearing people do. The researchers concluded that as the patients’ hearing recovers after the installation of the implants, their visual processing helps in processing auditory information. As a consequence, when their visual processing is already better at the outset, their speech comprehension has a higher potential for recovery.
his study has important implications for deaf people trying to decide whether cochlear implants are a viable option. For many, they have had a massive impact on their lives, so the decision is not an easy one to make, but knowing more about the role of neuroplasticity in the recovery of hearing may help visual processing activity become one more tool to use when deciding on a deaf person’s suitability for cochlear implants.