Cortical Reorganization and Multisensory Adaptation in Deaf ness and After Cochlear Implantation. A Systematic Literature Review

Abstract

Hearing loss reshapes the way the brain processes sound and vision. The central auditory system can reorganize after deafness and after cochlear implantation. This review brings together the evidence on cortical reorganization and multisensory adaptation in deaf people and in cochlear implant users.The aim was to synthesize studies that examined brain plasticity and audiovisual processing across different forms of hearing loss and to identify the themes that link these studies.A systematic search framework was applied across major databases. Studies were screened against defined inclusion and exclusion criteria. Fifteen studies formed the final corpus. Data were extracted on population and method and outcome and were synthesized through a thematic approach.The corpus covered cochlear implant users and people with single sided or asymmetric or unilateral hearing loss and typical hearing controls. Five themes emerged. These were cortical reorganization and audiovisual integration and speechreading rehabilitation and speech in noise outcomes and voice processing. Methods included positron emission tomography and functional magnetic resonance imaging and functional near infrared spectroscopy alongside behavioral testing.The evidence indicates that the deprived and the restored auditory brain recruits visual and multisensory resources to support speech understanding. These findings carry practical value for rehabilitation planning after cochlear implantation.