Cross-modal reorganization in cochlear implanted deaf patients: a brain imaging Pet study
J. Rouger, B. Fraysse, O. Deguine, Pascal Barone
Symposium Talk
Last modified: 2008-05-14
Abstract
Cochlear implants (CI) are neuroprostheses designed to restore speech perception in case of profound hearing loss. In a recent publication (Rouget et al PNAS 2007), we first demonstrated that deaf cochlear implant listeners developed high speech-reading skills during their period of deafness and maintained it several years after implantation, in spite of the progressive recovery of their auditory functions. Secondly, we showed that CI deaf patients present an over-normal ability to combine auditory and visual information synergistically, i.e. with a better performance than would be predicted by a simple probabilistic combination of the independent sensory streams.
To investigate more precisely the neural mechanisms underlying these cross-modal compensations in CI patients, we performed a longitudinal PET study. Cochlear implant patients (n = 11) were scanned few days after the implant onset and less than one year later, at the time their auditory speech comprehension score was greater than 80%. Speech comprehension was screened in visual-only (speechreading) and audiovisual conditions.
In cochlear-implant patients, visual speech induced activations of classical fusiform and occipital visual areas, as well as over-activations in associative auditory areas within the posterior STS (known to be involved in phonological processing), and in the right posterior inferior prefrontal region while showing deactivation of Broca’s area.
Audiovisual speech induced a potentiation of the associative auditory areas, showing an increase in observed activations. Remarkably, the leftward lateralization of speech and language processing observed in control subjects was not present in cochlear-implant patients, who showed a strong right lateralization in the first months following the implant onset. Moreover, as deaf people learn to use their cochlear implant, speech activations evolved to a more balanced lateralization.
Taken together, our data show that CI users quickly develop specific strategies of speech comprehension in order to process the coarse information provided by the cochlear prosthesis while the cortical networks involved in audiovisual speech integration underwent a progressive reorganization within a short time period of few months after implantation.
To investigate more precisely the neural mechanisms underlying these cross-modal compensations in CI patients, we performed a longitudinal PET study. Cochlear implant patients (n = 11) were scanned few days after the implant onset and less than one year later, at the time their auditory speech comprehension score was greater than 80%. Speech comprehension was screened in visual-only (speechreading) and audiovisual conditions.
In cochlear-implant patients, visual speech induced activations of classical fusiform and occipital visual areas, as well as over-activations in associative auditory areas within the posterior STS (known to be involved in phonological processing), and in the right posterior inferior prefrontal region while showing deactivation of Broca’s area.
Audiovisual speech induced a potentiation of the associative auditory areas, showing an increase in observed activations. Remarkably, the leftward lateralization of speech and language processing observed in control subjects was not present in cochlear-implant patients, who showed a strong right lateralization in the first months following the implant onset. Moreover, as deaf people learn to use their cochlear implant, speech activations evolved to a more balanced lateralization.
Taken together, our data show that CI users quickly develop specific strategies of speech comprehension in order to process the coarse information provided by the cochlear prosthesis while the cortical networks involved in audiovisual speech integration underwent a progressive reorganization within a short time period of few months after implantation.