Auditory- and visual-speech evoked activation of the superior temporal gyrus contralateral to the cochlear implant predicts speech understanding outcomes

Objective: Speech discrimination outcomes vary widely in cochlear implant recipients, but reasons for this variability are not well explained by patient history factors alone. Neuroplastic reorganisation after both deafness and cochlear implant switch-on can affect how new recipients adapt to electrical hearing. In this study, we evaluate the associations between speech understanding outcomes and stimulus evoked activation of cortical language processing areas. Design: 43 newly implanted post-lingually deaf adult cochlear implant recipients were recruited to the longitudinal study. Participants attended two research visits: the first conducted within one-month of device switch-on, and the second conducted one-year after device switch-on. At each visit, we evaluated speech understanding outcomes in noise and cortical activation using functional near infrared spectroscopy during a passive listening task, during which a story was told in either an auditory or visual-speech (lip-reading) condition. Results: We found statistically significant correlations between poorer speech understanding outcomes one year post device switch-on and large activations in the superior temporal gyrus contralateral to the device in response to both auditory- (F(1, 30) = 11.297, R2 = 0.274, p = 0.002) and visual-speech (F(1, 30) = 18.216, R2 = 0.38, p < 0.001) stimuli tested within one-month of switch-on. However, these significant associations were not observed using activation data from the one-year mark. Furthermore, we found no association between changes in activation of the superior temporal gyrus contralateral to the device and changes in speech understanding outcomes over the first year of implant use. Conclusions: Our evidence highlights that neuroplastic changes which occur following adult-onset deafness play an important role in how cochlear implant recipients adapt to their devices after switch-on. The relationship between neuroimaging measures made within one-month after device switch-on and speech understanding outcomes at one-year can potentially enable triaging of recipients to improve clinical management of implant recipients.