Two scientists used brain-imaging techniques to visualize the brain’s activity and view the reorganization of brain circuits while people start to lose their hearing. This allowed them to predict the success or failure of a cochlear implant amongst people who have become profoundly deaf in their adult life.

Diane Lazard, an ear, nose and throat surgeon at the Institut Vernes in Paris, and Anne-Lise Giraud, a neuroscientist at the University of Geneva's Faculty of Medicine, used functional neuroimaging to visualize the brain’s activity and see the reorganization of brain circuits while people start to lose their hearing.

Their study, published in Nature Communications, defines a cochlear implant as an electric device designed to counter the loss of hearing linked to an inner ear deficiency, either congenital or acquired. This device helps the majority of users to significantly improve their ability for oral understanding, yet there are a handful of adult patients who do not see improvements.

“The test went like this. We presented some visual stimuli to the subjects, in the form of written word, and asked them to determine whether two words, without the same orthographic ending, rhymed or not—for instance wait and gate. Subjects would then have to recourse to their memory of sounds and, using fMRI techniques, we observed the neural networks in action,” said Giraud in a press release. 

While the researchers expected their subjects to be slower and less accurate than those in a control group of people without difficulty of hearing, they found that certain deaf people completed the task more quickly and accurately than the controls. For "super-readers," whose brain circuits are in the right hemisphere and organized differently, cochlear implants led to poor results. For other deaf people who had the same speed during tasks as controlled subjects, they would benefit more from the implants.

This research points to the essential role played by the interactions between the auditory and visual systems in the success or failure of cochlear implants.