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The Journal of Neuroscience, July 18, 2007, 27(29):7838-7846; doi:10.1523/JNEUROSCI.0154-07.2007

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Development/Plasticity/Repair
Evidence of a Tonotopic Organization of the Auditory Cortex in Cochlear Implant Users

Jeanne Guiraud,^1,3,6 Julien Besle,^2,6 Laure Arnold,⁵ Patrick Boyle,⁵ Marie-Hélène Giard,^2,6 Olivier Bertrand,^2,6 Arnaud Norena,^1,6 Eric Truy,^1,4,6 and Lionel Collet^1,3,6

¹CNRS UMR 5020, Neurosciences and Sensorial Systems Laboratory, Lyon, F-69000, France, and ²INSERM, U821, Lyon, F-69500, France, Departments of ³Audiology and Otorhinolaryngology and ⁴Otolaryngology and Head and Neck Surgery, Edouard Herriot University Hospital, Lyon, F-69000, France, ⁵Clinical Research Department, Advanced Bionics, Cambridge CB22 5LD, United Kingdom, and ⁶ Université Lyon, Lyon, F-69000, France

Correspondence should be addressed to Jeanne Guiraud, Département d'Audiologie et ORL, Pavillon U, Hôpital Edouard Herriot, 5 place d'Arsonval, 69437 Lyon cedex 03, France. Email: jeanne_guiraud{at}hotmail.com

Deprivation from normal sensory input has been shown to alter tonotopic organization of the human auditory cortex. In this context, cochlear implant subjects provide an interesting model in that profound deafness is made partially reversible by the cochlear implant. In restoring afferent activity, cochlear implantation may also reverse some of the central changes related to deafness. The purpose of the present study was to address whether the auditory cortex of cochlear implant subjects is tonotopically organized. The subjects were thirteen adults with at least 3 months of cochlear implant experience. Auditory event-related potentials were recorded in response to electrical stimulation delivered at different intracochlear electrodes. Topographic analysis of the auditory N1 component (85 ms latency) showed that the locations on the scalp and the relative amplitudes of the positive/negative extrema differ according to the stimulated electrode, suggesting that distinct sets of neural sources are activated. Dipole modeling confirmed electrode-dependent orientations of these sources in temporal areas, which can be explained by nearby, but distinct sites of activation in the auditory cortex. Although the cortical organization in cochlear implant users is similar to the tonotopy found in normal-hearing subjects, some differences exist. Nevertheless, a correlation was found between the N1 peak amplitude indexing cortical tonotopy and the values given by the subjects for a pitch scaling task. Hence, the pattern of N1 variation likely reflects how frequencies are coded in the brain.

Key words: cortical tonotopy; cochlear implant; pitch perception; N1 topography; modeling; plasticity

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Received Jan. 15, 2007; revised May 29, 2007; accepted June 9, 2007.

Correspondence should be addressed to Jeanne Guiraud, Département d'Audiologie et ORL, Pavillon U, Hôpital Edouard Herriot, 5 place d'Arsonval, 69437 Lyon cedex 03, France. Email: jeanne_guiraud{at}hotmail.com

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