This lecture introduces the use of Functional Near-Infrared Spectroscopy (FNES) in understanding deafness and brain plasticity, particularly in cochlear implant patients. The instructor explains how FNES works, its advantages, limitations, and clinical applications. The lecture covers the correlation between FNES data and speech understanding, as well as the potential for FNES to improve clinical management of patients with implanted medical devices. Various studies and results are discussed, highlighting the importance of addressing both peripheral and central limitations in speech understanding. The lecture concludes with insights into potential strategies for modulating unusual brain activity and improving speech outcomes in cochlear implant users.