Auditory memory and cerebral reorganization in post-linguistically deaf adults

Transcription

1 Auditory memory and cerebral reorganization in post-linguistically deaf adults Implications for cochlear implantation outcome D Lazard, HJ Lee, E Truy, AL Giraud Ecole Normale Supérieure, Inserm U960, Paris, France Bionics Institute, Melbourne, Australia Hallym University College of Medicine, Anyang, Republic of Korea Hospices Civils de Lyon, Lyon, France

2 Introduction Phonological processing is more demanding for CI users Normal hearing controls vs. CI recipients: listening to words (PET) Phonological task Giraud et al. Brain Controls Phonological task Equal performance CI users Poor performers do not activate the superior temporal lobes nor the left inferior prefrontal cortex while listening to sentences Good Good vs. poor CI performers passively listening to sentences (PET) Poor Mortensen et al, NeuroImage, 2006

3 Neuro-functional hypothesis Stimulation Acoustic processing Phonological processing Cognitively more demanding Semantic processing Is phonological processing more difficult to achieve for postlinguistically deaf subjects and CI recipients? Are poor performers able to access the phonological content of the vocoded speech?

4 Investigation of phonological processing in deaf subjects candidates for a cochlear implantation

5 Experimental Paradigm Durations of deafness - Duration of hearing loss: date of beginning of moderate hearing loss or date of first hearing aids -Duration of auditory deprivation: date from which oral communication became extremely difficult despite optimal hearing aid rehabilitation

6 Experimental paradigm Phonological task in deaf adults and normal hearing controls : Cochlear Implantation 6 months Time fmri Rhyming task CI performance Word recognition scores (%) Poisson Garçon Non parametric tests

7 Phonological task in controls Left hemisphere Normal hearing subjects use the dorsal network = the phonological route Lazard et al. NeuroImage 2010

8 Phonological task in CI candidates Whole brain correlation with CI speech scores Left hemisphere Dorsal route <=> good performance Positive Correlation with CI performance Negative Correlation with CI performance Ventral route <=> poor performance Poor performers over-activate the semantic route when performing a phonological task Lazard et al. NeuroImage 2010

9 Phonological task in CI candidates Whole brain correlation with duration of hearing loss Left hemisphere Negative correlation with HL Positive Correlation with CI performance Positive correlation with HL Negative Correlation with CI performance The involvement of the dorsal route decreases in subjects with longer durations of hearing loss The activation of the left inferior frontal region increases with longer durations of hearing loss Lazard et al. NeuroImage 2010

10 Patients > Controls during the phonological task Overactivation of the right posterior temporal cortex Right hemisphere Contrast estimate rho = -0.88, p = 0.02 (n=8) Patients > Controls Deleterious adaptation? Contrast estimate Lazard et al. NeuroImage Phonological scores (%) rho = -0.77, p = 0.06 (n=7) CI performance (%)

11 The right posterior temporal cortex Usually processes prosody, para-linguistic & environmental sounds = Non-speech sound processing Right hemisphere Hickok et al. J Neurophysiol 2009 Lewis et al. Cerebral Cortex 2004 Halpern & Zatrorre. Cereb Cortex 1999

12 Posterior temporal cortices Left: phonological processing Right: non-speech sound processing Hickok et al. J Neurophysiol 2009 Lewis et al. Cerebral Cortex 2004 Halpern & Zatrorre. Cereb Cortex 1999

13 Posterior temporal cortices Comparative involvements in phonology and non-speech sound processing Cochlear Implantation 6 months Time fmri Rhyming and Imagery tasks Poisson Garçon CI performance Word recognition scores (%)

14 Phonological processing Left Contrast estimates P C * Right Contrast estimates P C ** Deaf subjects over-activate the posterior temporal cortices - left: more diffcult task - right: pathological reorganization Lazard et al HBM in press

15 Non-speech sound processing Left Contrast estimates P C ** Right Contrast estimates P C ** Deaf subjects do not activate the posterior temporal cortices: the right area is not recruited anymore for sound imagery Lazard et al HBM in press

16 Post-hoc correlation with durations of deafness Contrast estimates (AU) Left p=0.04; rho=-0.77; n=7 p=0.07; rho=-0.58; n= Duration of auditory deprivation (m) Phonology Sound imagery Contrast estimates (AU) Right p=0.05; rho=0.78; n=7 p=0.02; rho=-0.73; n= Duration of hearing loss (y) The physiological activations decrease with deafness while the right phonological overactivation increases. The right modifications start earlier than the left modifications.

17 Post-hoc correlation with CI performance Contrast estimates (AU) Left p=0.02; rho=0.85; n=7 p=0.77; rho=-0.10; n= Speech scores with the CI (%) Phonology Sound imagery Contrast estimates (AU) Right p=0.04; rho=-0.77; n=7 p=0.03; rho=0.66; n= Speech scores with the CI (%) The physiological activations correlate positively with CI outcomes The right phonological reorganization is maladaptive

18 Conclusion - Phonological and non-speech sound processing deteriorate with increasing durations of deafness = are not kept active by auditory inputs - The decline of non-speech sound processing releases cognitive resources that may be recycled to process phonology = Specific cerebral reorganization that aims to help oral communication

19 Conclusion This plasticity may be maladaptive relying on non-dedicated areas All types of auditory processing should be trained in order to keep active functional analytic networks

20 Perspectives 1. Cognitive rehabilitation from the beginning of moderate HL: based on phonological unit segmentation and auditory memory 2. Preoperative screening using behavioral tests: revealing patients using mainly their ventral semantic route to offer them a specific rehabilitation enhancing the dorsal route