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The Journal of Neuroscience, May 27, 2009, 29(21):7065-7078; doi:10.1523/JNEUROSCI.6072-08.2009

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Behavioral/Systems/Cognitive
Realignment of Interaural Cortical Maps in Asymmetric Hearing Loss

Steven W. Cheung,¹ Ben H. Bonham,¹ Christoph E. Schreiner,¹ Benoit Godey,² and David A. Copenhaver¹

¹Coleman Memorial Laboratory and Keck Center for Integrative Neuroscience, Department of Otolaryngology-Head and Neck Surgery, University of California, San Francisco, San Francisco, California 94143-0342, and ²Laboratoire IDM, UPRES-EA 3192, Faculté de Médecine, Université de Rennes I, CS 34317, 35043 Cedex, Rennes, France

Correspondence should be addressed to Dr. Steven W. Cheung, Otology, Neurotology, and Skull Base Surgery, University of California, San Francisco, Parnassus Avenue, San Francisco, CA 94143-0342. Email: scheung{at}ohns.ucsf.edu

Misalignment of interaural cortical response maps in asymmetric hearing loss evolves from initial gross divergence to near convergence over a 6 month recovery period. The evolution of left primary auditory cortex (AI) interaural frequency map changes is chronicled in squirrel monkeys with asymmetric hearing loss induced by overstimulating the right ear with a 1 kHz tone at 136 dB for 3 h. AI frequency response areas (FRAs), derived from tone bursts presented to the poorer or better hearing ears, are compared at 6, 12, and 24 weeks after acoustic overstimulation. Characteristic frequency (CF) and minimum threshold parameters are extracted from FRAs, and they are used to quantify interaural response map differences. A large interaural CF map misalignment of CF 1.27 octaves at 6 weeks after overstimulation decreases substantially to CF 0.62 octave at 24 weeks. Interaural cortical threshold map misalignment faithfully reflects peripheral asymmetric hearing loss at 6 and 12 weeks. However, AI threshold map misalignment essentially disappears at 24 weeks, primarily because ipsilateral cortical thresholds have become unexpectedly elevated relative to peripheral thresholds. The findings document that plastic change in central processing of sound stimuli arriving from the nominally better hearing ear may account for progressive realignment of both interaural frequency and threshold maps.

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Received Dec. 21, 2008; revised April 20, 2009; accepted April 25, 2009.

Correspondence should be addressed to Dr. Steven W. Cheung, Otology, Neurotology, and Skull Base Surgery, University of California, San Francisco, Parnassus Avenue, San Francisco, CA 94143-0342. Email: scheung{at}ohns.ucsf.edu

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