Submitted on November 6, 2007
Accepted on January 15, 2008
Sound Localization Deficits During Reversible Deactivation of Primary Auditory Cortex and/or the Dorsal Zone
Shveta Malhotra1, G. Christopher Stecker2, John C Middlebrooks3, and Stephen G Lomber4*
1 School of Behvaioral and Brain Sciences, University of Texas at Dallas, Richardson, Texas, United States
2 Speech & Hearing Sciences, University of Washington, Seattle, Washington, United States
3 Kresge Hearing Institute, Ann Arbor, Michigan, United States; Kresge Hearing Institute, United States
4 Dept. of Physiology, University of Western Ontario, London, Canada
* To whom correspondence should be addressed. E-mail: steve.lomber{at}uwo.ca.
We examined the contributions of primary auditory cortex (AI) and the dorsal zone of auditory cortex (DZ) to sound localization behavior during separate and combined unilateral and bilateral deactivation. Cats learned to make an orienting response (head movement and approach) to a 100-ms broad-band noise burst emitted from a central speaker or one of 12 peripheral sites (located in front of the animal, from left 90˚ to right 90˚, at 15˚ intervals) along the horizontal plane. Following training, each cat was implanted with separate cryoloops over AI and DZ bilaterally. Unilateral deactivation of AI or DZ or simultaneous unilateral deactivation of AI and DZ (AI/DZ) resulted in spatial localization deficits confined to the contralateral hemifield. Simultaneous bilateral deactivation of both AI and DZ resulted in sound localization performance dropping from near-perfect to chance (7.7% correct) across the entire field. However, unlike the profound sound localization deficit that occurs when AI and DZ are deactivated together, deactivation of either AI or DZ alone produced partial and field-specific deficits. For AI, bilateral deactivation resulted in higher error rates (performance dropping to ~45%) but relatively small errors (mostly within 30 degrees of the target). In contrast, bilateral deactivation of DZ produced somewhat fewer errors (performance dropping only to ~60% correct), but the errors tended to be larger, often into the incorrect hemifield. Therefore, individual deactivation of either AI or DZ produced specific and unique sound localization deficits.
