COCHLEAR IMPLANT EFFICIENCY IN PRELINGUALLY AND POSTLINGUALLY DEAF SUBJECTS - A STUDY WITH (H2O)-O-15 AND PET

We used O-15-labelled water in a PET study to test the efficiency of c ochlear implants (CIs) in transmitting auditory information to the bra in in 10 profoundly deaf subjects. Five were postlingually deaf and fi ve were prelingually deaf All the subjects were right-handed White noi se and verbal stimuli, delivered through the CIs, were used for cortic al activation. Similar tasks were performed by six right-handed hearin g subjects as a control group. In the postlingually deaf subjects, ver bal stimulation activated the transverse temporal gyri (primary audito ry cortices) mainly on the side contralateral to the CI. The left post erior superior temporal gyrus (Wemicke's area), and the left inferior frontal gyrus (Broca's area) were also activated irrespective of stimu lated side. The location of these activated foci was the same as that of the control group. White noise stimulation led to an increase of re gional cerebral bloodflow (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 w ith verbal stimulation. In the prelingually deaf subjects, Wernicke's area and Broca's area were significantly activated by verbal stimulati on, whereas there was no activation in the primary auditory cortices. White noise did not activate the primary auditory cortex in the prelin gually subjects. These findings: suggest that cortical representation of language is not dependent on early auditory experience, while proce ssing in the primary auditory cortices is experience-dependent. The po stlingually deaf subjects had a greater increase of rCBF in the Broca' s and Wernicke's areas and better sentence comprehension than the prel ingually deaf subjects, which suggests a parallel relation between rCB F increase and the ability to recognize spoken language. (H2O)-O-15-PE T with auditory stimulation is apt effective means of objectively quan tifying the response of auditory and association cortices after CIs in deaf subjects.