Cochlear implant efficiency in pre- and postlingually deaf subjects. A study with H2(15)O and PET

We used 15O-labelled water in a PET study to test the efficiency of cochlear implants (CIs) in transmitting auditory information to the brain in 10 profoundly deaf subjects. Five were postlingually deaf, and five were prelingually deaf. All the subjects were right-handed. White noise and verbal stimuli, delivered through the CIs, were used for cortical activation. Similar tasks were performed by six right-handed hearing subjects as a control group. In the postlingually deaf subjects, verbal stimulation activated the transverse temporal gyri (primary auditory cortices) mainly on the side contralateral to the CI. The left posterior superior temporal gyrus (Wernicke's area), and the left inferior frontal gyrus (Broca's area) were also activated irrespective of stimulated side. The location of these activated foci was the same as that of the control group. White noise stimulation led to an increase of regional cerebral blood flow (rCBF) only in the primary auditory cortices of the postlingually deaf subjects, only on the side contralateral to the CI, and the intensity of activation was less than that obtained with verbal stimulation. In the prelingually deaf subjects, Wernicke's area and Broca's area were significantly activated by verbal stimulation, whereas there was no activation in the primary auditory cortices. White noise did not activate the primary auditory cortex in the prelingually subjects. These findings suggest that cortical representation of language is not dependent on early auditory experience, while processing in the primary auditory cortices is experience-dependent. The postlingually deaf subjects had a greater increase of rCBF in the Broca's and Wernicke's areas and better sentence comprehension than the prelingually deaf subjects, which suggest a parallel relation between rCBF increase and the ability to recognize spoken language. H2(15)O-PET with auditory stimulation is an effective means of objectively quantifying the response of auditory and association cortices after CIs in deaf subjects.