Pascal Barone - "Recovery of auditory functions in cochlear implanted deaf subjects : psychophysics and brain imaging approaches"

ABSTRACT
A cochlear implant (CI) allows post-lingual adult deaf patients to understand speech through long-term adaptative processes to build coherent percepts from the coarse information delivered by the implant. Because the success of rehabilitations relies on the functional plasticity in the auditory system, it is of crucial importance to understand the reorganization of the cortical network involved in speech comprehension that occurs during deafness and following the progressive recovery.
As a consequence of a long period of deafness and because of the crude information provided by the implant, CI users have developed compensatory strategies for speech comprehension favoring speech-reading and visuo-auditory interactions. While they are recovering the auditory function, CI patients preserve high skills of speech reading even several years after implantation. This high visual aptitude induces supranormal audiovisual integration. For example, we have shown that voice cognitive abilities that are important for social interactions (gender and speaker identification, voice emotion recognition) remain deficient in CI patients and are strongly influenced by the visual modality.
Because of the neuro-prosthesis, only PET scan (Positron emission tomography) neuro-imaging studies can be performed to visualize brain activity based on regional changes in cerebral blood flow. We will present recent evidences that the of cross-modal compensation observed at the behavioral level is accompanied by plastic changes in the visual and auditory network involved in speech integration. Visual and visuo-auditory based strategies in CI patients are expressed by cross-modal activations that affect the auditory areas of the posterior temporal cortex and the auditory voice area buried in STS. These cross-modal activations declined during the first year post-implantation in parallel with a re-activation of the speech perception/production loop involving Broca’s area, reflecting the progressive recovery of the predominance of auditory input in auditory speech processing areas.
Altogether, our findings shed lights on the importance of the synergic audiovisual integration in CI patients in fastening their progressive recovery. Consequently, speech rehabilitation strategies should explicitly include intensive audiovisual stimulation.

ABOUT PASCAL BARONE
The diverse fields of research that I have conducted have all in common a search for relationships between brain structures and functions. I have follow this quest using multiple tools (neuro-anatomy, electrophysiology, psychophysics and brain imaging) and theoretical strategies, from development to adult plasticity.
I received my Phd in 1989 (Univ. Lyon I) on a work which was pioneer in the use of sequencing paradigms to demonstrate at the neuronal level, the role of the prefrontal cortex in the control of the temporal organization of behaviors.
During postdoctoral fellowship in Dr Imig’s laboratory (Kansas Univ) my research activity aimed at the neuronal mechanisms involved in sound localization in the primary auditory cortex of the cat. I did a second postdoc with Dr Kennedy (Inserm, Lyon) before getting a CNRS position in 1996. I was exploring the neuronal mechanisms of axogenesis in the developing monkey.
Since 2001 in the CerCo (Toulouse) I conduct anatomical and electrophysiological works to demonstrate that multisensory integration can occur at early stages of sensory processing, arguing against a hierarchical model of this mechanism. This basic research conducted my interest toward clinical research in cochlear implanted deaf patients to work on cross-modal compensation and functional reorganization of the cortical network involved in speech comprehension.
Since several years, I have established a strong link with the clinical research team of Prof B. Fraysse and O. Deguine (CHU Purpan, Toulouse). Because the success of rehabilitations relies on the functional plasticity in the auditory system, our project is aimed at understanding the reorganization of the cortical network involved in speech comprehension that occurs during deafness and following the progressive recovery. Our proposal is based on a multidisciplinary approach at both a fundamental and a clinical levels, it encompasses behavioral and brain imaging (PET) studies in patients as well as in normal hearing subjects experimenting the simulation of the processing performed by a cochlear implant. Our complementary projects aim to a better understanding of hearing restoration coupled to the evaluation of rehabilitation strategies.