Malhotra Shveta, Stecker G Christopher, Middlebrooks John C, Lomber Stephen G
Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada.
J Neurophysiol. 2008 Apr;99(4):1628-42. doi: 10.1152/jn.01228.2007. Epub 2008 Jan 16.
We examined the contributions of primary auditory cortex (A1) and the dorsal zone of auditory cortex (DZ) to sound localization behavior during separate and combined unilateral and bilateral deactivation. From a central visual fixation point, cats learned to make an orienting response (head movement and approach) to a 100-ms broadband noise burst emitted from a central speaker or one of 12 peripheral sites (located in front of the animal, from left 90 degrees to right 90 degrees, at 15 degrees intervals) along the horizontal plane. Following training, each cat was implanted with separate cryoloops over A1 and DZ bilaterally. Unilateral deactivation of A1 or DZ or simultaneous unilateral deactivation of A1 and DZ (A1/DZ) resulted in spatial localization deficits confined to the contralateral hemifield, whereas sound localization to positions in the ipsilateral hemifield remained unaffected. Simultaneous bilateral deactivation of both A1 and DZ resulted in sound localization performance dropping from near-perfect to chance (7.7% correct) across the entire field. Errors made during bilateral deactivation of A1/DZ tended to be confined to the same hemifield as the target. However, unlike the profound sound localization deficit that occurs when A1 and DZ are deactivated together, deactivation of either A1 or DZ alone produced partial and field-specific deficits. For A1, bilateral deactivation resulted in higher error rates (performance dropping to approximately 45%) but relatively small errors (mostly within 30 degrees of the target). In contrast, bilateral deactivation of DZ produced somewhat fewer errors (performance dropping to only approximately 60% correct), but the errors tended to be larger, often into the incorrect hemifield. Therefore individual deactivation of either A1 or DZ produced specific and unique sound localization deficits. The results of the present study reveal that DZ plays a role in sound localization. Along with previous anatomical and physiological data, these behavioral data support the view that A1 and DZ are distinct cortical areas. Finally, the findings that deactivation of either A1 or DZ alone produces partial sound localization deficits, whereas deactivation of either posterior auditory field (PAF) or anterior ectosylvian sulcus (AES) produces profound sound localization deficits, suggests that PAF and AES make more significant contributions to sound localization than either A1 or DZ.
我们研究了初级听觉皮层（A1）和听觉皮层背侧区（DZ）在单侧和双侧失活单独及联合作用期间对声音定位行为的贡献。猫从中央视觉注视点出发，学会对从中央扬声器或沿水平面12个外周位置（位于动物前方，从左90度到右90度，间隔15度）之一发出的100毫秒宽带噪声爆发做出定向反应（头部移动和靠近）。训练后，给每只猫双侧A1和DZ上方分别植入冷冻环。单侧失活A1或DZ，或同时单侧失活A1和DZ（A1/DZ）会导致空间定位缺陷局限于对侧半视野，而对同侧半视野位置的声音定位则不受影响。同时双侧失活A1和DZ会导致整个视野内声音定位表现从接近完美降至随机水平（正确率7.7%）。A1/DZ双侧失活期间出现的错误往往局限于与目标相同的半视野。然而，与A1和DZ一起失活时出现的严重声音定位缺陷不同，单独失活A1或DZ会产生部分且特定于视野的缺陷。对于A1，双侧失活导致错误率更高（表现降至约45%），但错误相对较小（大多在目标的30度范围内）。相比之下，DZ双侧失活产生的错误略少（表现降至仅约60%正确），但错误往往更大，常常进入错误的半视野。因此，单独失活A1或DZ会产生特定且独特的声音定位缺陷。本研究结果表明DZ在声音定位中起作用。连同先前的解剖学和生理学数据，这些行为数据支持A1和DZ是不同皮层区域的观点。最后，单独失活A1或DZ会产生部分声音定位缺陷，而后听觉场（PAF）或前外侧沟（AES）单独失活会产生严重声音定位缺陷，这一发现表明PAF和AES对声音定位的贡献比A1或DZ更大。
