Hearing through sight

November 8, 2013
Hearing through sight
Fig implants cochleaires X-ray image of a cochlear implant. Credit: CERCO and Purpan Hospital

Cochlear implants allow adults who have become profoundly deaf to recover the ability to understand speech. However, recovery differs between individuals. Activating the visual regions of the brain has proved essential to the satisfactory recovery of hearing, according to a new study by the Centre de Recherche Cerveau et Cognition (CERCO, CNRS/Université Toulouse III - Paul Sabatier), carried out in close collaboration with the ENT department at Hôpital Purpan in Toulouse. The more the area of the brain responsible for vision is activated immediately after implantation, the better the individual's speech understanding performance six months later. There is therefore a synergy between sight and hearing, resulting in a gradual improvement in the decoding of speech. These findings, which have just been published in Brain, illustrate the crucial role of brain plasticity. And they may make it possible to develop diagnostic tools for specific rehabilitation.

Cochlear are an effective alternative for people suffering from profound deafness (with a hearing threshold greater than 90 decibels) to emerge from a silent world. Implanted in the inner ear during a surgical procedure, these auditory neural prostheses transform external sounds into electrical impulses that directly stimulate the , leading to a marked recovery of hearing capacity. On average, people who, after becoming deaf, could only recognize one in five words before implantation are able to distinguish more than 80% of words afterwards. However, the degree of recovery may vary on an individual basis.

What is the origin of this disparity? The signal delivered by the implant is significantly degraded, thus obliging patients to develop adaptive strategies. Their performance will therefore depend on how their brain adapts in order to decode the signal. The CERCO scientists estimated that the brain's capacity for plasticity may play a fundamental role in the success of rehabilitation using a cochlear implant. To support this hypothesis, they wondered whether it was possible to identify the brain regions whose activation is essential to a good recovery, as well as predict the potential for recovery of patients, based on the state of activity of these regions at the time of implantation.

Their study concerned 10 patients who had become deaf in adulthood after language acquisition, and who had recently received an implant. The scientists performed a PET (positron emission tomography) brain imaging session immediately after insertion of the implant: they then recorded the level of activation in each region of the brain during a simple test (which involved identifying whether the "sound" perceived was a word or not). Six months later, the research team measured the degree of recovery of the same patients using more elaborate word recognition tests. The final stage consisted in drawing a correlation diagram for each brain region under study. The researchers thus evidenced two types of brain regions. The first group notably included the visual cortex and prefrontal cortex, which are associated with language learning and production: the greater the activation of these regions at the time of implantation, the higher the degree of recovery six months later.

Surprisingly, the brain regions processing visual information were thus correlated to auditory rehabilitation. Thus, the stronger the activation in patients' visual cortex at the time of implantation, the better they could understand speech six months later. According to the scientists, this result was linked to the fundamental role of lip reading in auditory speech recovery. Vision thus supplies additional information that is crucial to understanding language, particularly in noisy environments where patients with sometimes find it difficult to distinguish words. Sight and hearing act together and in total synergy, thus helping to gradually improve patients' ability, as they recover, to decipher the words coded by the implant.

These results highlight the crucial role of in implanted patients. This role could also be key in any other rehabilitation mechanism using a neural prosthesis (affecting vision or motor functions, for example). In addition, these findings could make it possible to predict the level of recovery that an implanted patient will achieve. Based on objective imaging data, it may be possible to implement individual, more or less intensive speech therapy rehabilitation, relying on an adapted strategy aimed at familiarizing each patient with the implant (hearing, lip reading and/or visual-auditory interactions). The efficacy of this type of targeted rehabilitation should help rationalize the cost of caring for these patients.

Explore further: World-first device offers new insight into life with a cochlear implant

More information: "Visual activity predicts auditory recovery from deafness after adult cochlear implantation." Kuzma Strelnikov, Julien Rouger, Jean-François Demonet, Sebastien Lagleyre, Bernard Fraysse, Olivier Deguine and Pascal Barone. Brain (2013). Published online on October 17, 2013 and in print in December 2013. DOI: 10.1093/brain/awt274

Related Stories

World-first device offers new insight into life with a cochlear implant

October 30, 2013
A new imaging device will be launched on Macquarie University's campus today, helping researchers in the ARC Centre of Excellence in Cognition and its Disorders (CCD) and HEARing Cooperative Research Centre (CRC) better understand ...

New strategy lets cochlear implant users hear music

October 9, 2013
For many, music is a universal language that unites people when words cannot. But for those who use cochlear implants—technology that allows deaf and hard of hearing people to comprehend speech—hearing music remains extremely ...

Two bionic ears are better than the sum of their parts

September 20, 2012
Cochlear implants—electronic devices surgically implanted in the ear to help provide a sense of sound—have been successfully used since the late 1980's. But questions remain as to whether bilateral cochlear implants, ...

Scientists track the genes behind hearing loss

September 24, 2013
Tens of millions of Europeans suffer from a hearing impairment of some degree. They range from the one child in 1,000 who is born deaf, to the many whose hearing is declining as they grow older.

Deaf brain processes touch differently, study shows

July 10, 2012
People who are born deaf process the sense of touch differently than people who are born with normal hearing, according to research funded by the National Institutes of Health. The finding reveals how the early loss of a ...

Recommended for you

Brain stimulation may improve cognitive performance in people with schizophrenia

July 24, 2017
Brain stimulation could be used to treat cognitive deficits frequently associated with schizophrenia, according to a new study from King's College London.

New map may lead to drug development for complex brain disorders, researcher says

July 24, 2017
Just as parents are not the root of all their children's problems, a single gene mutation can't be blamed for complex brain disorders like autism, according to a Keck School of Medicine of USC neuroscientist.

Bird songs provide insight into how developing brain forms memories

July 24, 2017
Researchers at the University of Chicago have demonstrated, for the first time, that a key protein complex in the brain is linked to the ability of young animals to learn behavioral patterns from adults.

Research identifies new brain death pathway in Alzheimer's disease

July 24, 2017
Alzheimer's disease tragically ravages the brains, memories and ultimately, personalities of its victims. Now affecting 5 million Americans, Alzheimer's disease is the sixth leading cause of death in the U.S., and a cure ...

Illuminating neural pathways in the living brain

July 24, 2017
Using light alone, scientists from the Max Planck Institute of Neurobiology in Martinsried are now able to reveal pairs or chains of functionally connected neurons under the microscope. The new optogenetic method, named Optobow, ...

Working around spinal injuries: Rehabilitation, drug treatment lets rats recover some involuntary movement

July 24, 2017
A new study in rats shows that changes in the brain after spinal cord injury are necessary to restore at least some function to lower limbs. The work was published recently in the journal eLife.

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Nov 08, 2013
Great news.
The motion of lips to aid a construct of the signals processed in the brain send via the auditory nerve.
Is the motion we must use to read (scanning) a contributing precursor to this (in people lacking impairment) improved ability of motion constructs?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.