Phonological processing in post-lingual deafness and cochlear implant outcome

Cochlear implants work well, yet the outcome is not fully accounted by the data routinely available to the clinician, and remains unpredictable. A more in-depth understanding of the neural mechanisms that determine the clinical recovery after cochlear implantation is warranted, as they may provide the background for an accurate individual prognosis. In this study in post-lingually deaf adults, we show that while clinical data offer only prognosis trends, fMRI data can prospectively distinguish good from poor implant performers. We show that those deaf cochlear implant (CI) candidates who will become good performers rely on a dorsal phonological route when performing a rhyming task on written regular words. In contrast, those who will become poor performers involve a ventral temporo-frontal route to perform the same task, and abnormally recruit the right supramarginal gyrus, a region that is contralateral to classical phonological regions. These functional patterns reveal that deafness either enhances “normal” phonological processing, or prompts a substitution of phonological processing by lexico-semantic processing. These findings thus suggest that a simple behavioral pre-operative exploration of phonological strategies during reading, to determine which route is predominantly used by CI candidates, might fruitfully inform the outcome.