The mismatch negativity (MMN) brain response to sound frequency changes in adult cochlear implant recipients: a follow-up study

Conclusion: Plasticity of auditory pitch discrimination driven by cochlear implant (CI) use uring a 2.5-year follow-up was indicated by an enhancement of the amplitude of mismatch negativity (MMN) event-related brain potential (ERP) to pure tone frequency changes. Objectives: To follow up changes in MMN elicited to frequency and duration changes in tones during 2.5 years of CI use and to compare MMN results with audiometric speech recognition scores (SRSs). Methods: Postlingually deafened adults with Cochlear Nucleus CI-22 and spectra processor with SPEAK strategy were recruited. MMN was measured at 1 and 2.5 years after CI activation. Repetitive 100 ms standard tones with a frequency of 500, 1000, 2000 or 4000 Hz in separate sequences were delivered to participants concentrating on a silent movie. Deviant tones occurring infrequently among standard tones were 20% lower in frequency or 50% shorter in duration than the standards. Speech recognition ability was followed with SRSs. Results: Both time from CI activation and the frequency range of tones had significant effects on the MMN amplitude. A significant enhancement was observed for theMMNelicited by 3200 Hz deviant tones among 4000 Hz standards. Also SRSs significantly increased with time and correlated with MMN amplitudes to the 3200 Hz deviants in both measurements.