Functional brain imaging of speech perception via electrical stimulation

In order to examine factors contributing to speech perception performance variations in cochlear implant users, single photon emission computed tomography (SPECT) was used to examine cortical activity (regional cerebral blood flow, rCBF) elicited by the electrical stimulation of multichannel cochlear implants. Normal hearing (N = 9) and cochlear implant (N = 8) subjects watched a 15 minute video-taped story under two conditions: audio presented monaurally to the left ear (implanted for cochlear implant subjects), and a visual only presentation. Left monaural stimulation in normal hearing subjects produced significant bilateral activation of Brodmann areas 41, 42, 22, 21, and 38. Cochlear implant subjects with relatively high levels of open-set speech perception demonstrated bilateral activation of cortex; however, the extent of activation was significantly less than that observed for normal hearing individuals, particularly in auditory association cortex (Brodmann areas 22, 21, 38). Individuals with minimal open set speech perception scores demonstrated unilateral activation of the cortex on the hemisphere contralateral to the ear of implantation, with minimal auditory association cortex activation.