Preoperative functional assessment of auditory cortex in adult cochlear implant users

Objectives: To explore functional neuroanatomical responses to auditory sti mulation before and after implantation. Study Design: A prospective study o f three cochlear implant candidates (pure-tone averages of 90 dB HL or grea ter bilaterally and hearing in noise test [HINT] performances of <40%) in w hich regional cerebral blood flow (rCBF) was assessed using single photon e mission computed tomography (SPECT), Methods: Candidates watched a 15-minut e videotaped story under four conditions: audio presented monaurally in the right and left ears (aided), audio presented binaurally (aided), and visua l-only presentation of the story. Five minutes into each story, 20 to 25 mC i of technetium 99m (Tc-99m) hexamethyl-propyleneamine-oxime (HMPAO) (Cerat ec; Nycomed Amersham, Princeton, NJ, U.S.A) was injected over a 30-second p eriod to ensure that subjects were unaware of tracer administration, Subjec ts were scanned for 20 minutes using a PRISM 3000 gamma camera (Picker Inte rnational, Cleveland, OH, U.S.A). Data were normalized and do-registered, a nd subtraction images were compiled. Subtraction images contrasted activati on patterns generated under the visual-only control condition to the audito ry activation states acquired monaurally and binaurally. Results: Right and left ear monaural stimulation in normal hearing subjects resulted in signi ficant bilateral activation of Brodmann areas 41, 42, 21, 22, and 38, Altho ugh substantial intersubject response variability was noted, subjects gener elly failed to bilaterally activate these areas under monaural hearing aid presentations; however, bilateral activation of areas 41 and 22 was noted u nder binaural presentations. Conclusions: Despite relatively similar hearin g losses in each ear, significant differences in preoperative auditory cort ex activation were observed between ears, These data suggest that functiona l brain imaging provides a useful tool for exploring the responsiveness of the auditory cortex in cochlear implant candidates.