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Cerebral Cortex Advance Access published online on November 11, 2009
Cerebral Cortex, doi:10.1093/cercor/bhp222
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© The Author 2009. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

Cortical Representation of Interaural Time Difference in Congenital Deafness

J. Tillein1,2, P. Hubka3,4, E. Syed1, R. Hartmann5, A.K. Engel1 and A. Kral1,3

1 Laboratory of Auditory Neuroscience, Department of Neurophysiology and Pathophysiology, University Medical Center Hamburg-Eppendorf, D-20246 Hamburg, Germany, 2 MedEl Elektromedizinische Geräte GmbH, A-6020 Innsbruck, Austria, 3 Laboratory of Auditory Neuroscience, Department of Experimental Otology, ENT Clinics, Medical University D-30625 Hannover, Germany, 4 Institute of Pathological Physiology, Comenius University School of Medicine, SK-81108 Bratislava, Slovak Republic, 5 Institute of Sensory Physiology and Neurophysiology, J.W.Goethe University Hospital, D-60590 Frankfurt am Main, Germany

Address correspondence to Dr A. Kral, Department of Experimental Otology, ENT-Clinics, Medical University Hannover, 30625 Hannover, Germany. Email: a.kral{at}uke.uni-hamburg.de

Binaural cues are required for localization of sound sources. In the present paper, representation of binaural cues has been investigated in the adult auditory cortex. Hearing and congenitally deaf cats were stimulated through binaural cochlear implants and unit responses were collected in the subregion of field A1 showing the largest amplitudes of evoked local field potentials. Sensitivity to interaural time difference (ITD) in the range from –600 to 600 µs was tested at intensities of 0–10 dB above hearing threshold. Template ITD functions were fitted to the data and parameters of ITD functions were compared between deaf and hearing animals. In deaf animals, fewer units responded to binaural stimulation, and those that responded had smaller maximal evoked firing rate. The fit to the template ITD functions was significantly worse in deaf animals, and the modulation depth in ITD functions was smaller, demonstrating a decrease in ITD sensitivity. With increasing binaural levels, hearing controls demonstrated systematic changes in ITD functions not found in deaf animals. Bimodal responses, likely related to precedence effect, were rare in deaf animals. The data demonstrate that despite some rudimentary sensitivity to interaural timing, cortical representation of ITDs is substantially altered by congenital auditory deprivation.

Key Words: auditory deprivation • binaural • cochlear implant • development • spatial hearing

J. Tillein and P. Hubka contributed to the study equally.


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