MONITORING THE COCHLEAR MICROENVIRONMENT USING ELECTROCHEMICAL SENSING WITH A COCHLEAR IMPLANT

Cochlear implants (CIs) are highly successful neural prostheses that compensate for hearing loss by electrically stimulating the auditory nerve. Additionally, CIs can serve as electrochemical sensors, as recently demonstrated in acutely implanted rats. This novel application enables monitoring of the cochlear microenvironment and electrode condition. Here, we investigate the influence of different anesthetics on electrochemical CI sensing and investigate the feasibility of such measurements in the awake state. Adult deafened Wistar rats were bilaterally implanted with 3-electrode CI arrays and underwent several months of sound lateralization training and electrochemical measurements. Measurements included electrode characterization by cyclic voltammetry and intracochlear oxygen sensing using combined chronoamperometric and potentiometric methods. Experiments were conducted under isoflurane anesthesia, ketamine/xylazine anesthesia, and in the awake state. CI sensing using standard CI electrodes was feasible under all conditions for up to 5 months without affecting behavioral lateralization training. Electrode characterization showed comparable features in ketamine/xylazine-anesthetized and awake states, whereas sensing characteristics were substantially altered under isoflurane anesthesia. Furthermore, stable and reproducible measurements of intracochlear oxygen levels were obtained over several months. The electrochemical sensing in awake rats did not induce behavioral changes during measurements. These findings demonstrate that long-term electrochemical sensing is possible with standard implant electrodes, enabling monitoring of the cochlear microenvironment not only under anesthesia but also in awake animals. This approach provides access to processes at the neuron–implant interface, including foreign body responses, and represents a step toward the clinical translation of intracochlear electrochemical sensing in human CI users.