CORTICAL ACTIVATION IN PROFOUNDLY DEAF PATIENTS DURING COCHLEAR IMPLANT STIMULATION DEMONSTRATED BY H2O-15 PET

Cochlear implants (CIs) are used to provide sensations of sound to profoundly deaf patients. The performance of the CI is assessed mainly by the subjective reports of patients. The aim of this study was to look for objective cortical responses to the stimulation of the CI. Two postlingually and two prelingually deaf patients were investigated by positron emission tomography (PET) using O-15-labeled water ((H2O)-O-15) to determine the region cerebral blood flow (rCBF). Instead of quantifying rCBF in absolute terms, it was estimated by referring the regional tissue concentration of (H2O)-O-15 to the mean whole brain concentration. CI stimulation encoded from white noise and sequential words led to an increased rCBF in the primary and secondary (Wernicke) auditory cortex. Relative elevations of up to 33% were observed bilaterally, although they were higher contralateral to the CI. These results were obtained not only in the postlingually deaf patients but also in two patients who had never been able to hear. Thus, it could be demonstrated that PET measurements of cerebral (H2O)-O-15 distribution yield objective responses of the central auditory system during electrical stimulation by CIs in profoundly deaf patients.