REGIONAL CEREBRAL ACTIVATION DURING AUDITORY-STIMULATION IN PATIENTS WITH COCHLEAR IMPLANTS

Objective: To evaluate a possible change in the regional cerebral blood flow (rCBF) in the language-related cortical areas of the brain during stimulation of a cochlear implant. Methods: The rCBF was measured by single-photon emission tomography and inhalation of Xenon Xe 133, providing information on the regional functional level of the brain. A supplementary single-pho ton emission tomographic scan was also performed, using technetium Te 99m hexamethylpropyleneamineoxime as a flow marker. The rCBF was measured during rest (baseline) and during auditory stimulation by presenting white noise and running speech to the ear with the implant. Patients: Five deaf patients who had undergone intracochlear or extracochlear implantation surgery. Results: As in subjects with normal hearing, notable activation was not found in the relevant primary auditory cortex on stimulation with white noise. Two of the patients with implants had an increase in the rCBF in the relevant contralateral hemisphere on stimulation with running speech, but in the other three patients, a notable increase was not detected. This lack of increase in the rCBF on speech stimulation was consistent with the lack of speech recognition experienced by the subjects when using the implant. In one subject, the implant had a beneficial effect on speech understanding that was associated with a significant increase in the cerebral blood flow in the Broca's speech area and Wernicke's second speech area. Conclusions: Although the results are preliminary, the single-photon emission tomographic technique may be useful when evaluating the function of a cochlear implant. The method may also help select patients and/or ears for cochlear implantation. Four of five patients had functional defects of auditory relevant cortical areas, suggesting that their deafness might be associated with central impairment in addition to their cochlear defects.