Department of Neurobiology and Behavior, University of California at Irvine, Irvine, California;
J Neurophysiol. 2013 Nov;110(9):2140-51. doi: 10.1152/jn.00219.2013. Epub 2013 Aug 14.
The rat is a widely used species for study of the auditory system. Psychophysical results from rats have shown an inability to discriminate sound source locations within a lateral hemifield, despite showing fairly sharp near-midline acuity. We tested the hypothesis that those characteristics of the rat's sound localization psychophysics are evident in the characteristics of spatial sensitivity of its cortical neurons. In addition, we sought quantitative descriptions of in vivo spatial sensitivity of cortical neurons that would support development of an in vitro experimental model to study cortical mechanisms of spatial hearing. We assessed the spatial sensitivity of single- and multiple-neuron responses in the primary auditory cortex (A1) of urethane-anesthetized rats. Free-field noise bursts were varied throughout 360° of azimuth in the horizontal plane at sound levels from 10 to 40 dB above neural thresholds. All neurons encountered in A1 displayed contralateral-hemifield spatial tuning in that they responded strongly to contralateral sound source locations, their responses cut off sharply for locations near the frontal midline, and they showed weak or no responses to ipsilateral sources. Spatial tuning was quite stable across a 30-dB range of sound levels. Consistent with rat psychophysical results, a linear discriminator analysis of spike counts exhibited high spatial acuity for near-midline sounds and poor discrimination for off-midline locations. Hemifield spatial tuning is the most common pattern across all mammals tested previously. The homogeneous population of neurons in rat area A1 will make an excellent system for study of the mechanisms underlying that pattern.
老鼠是研究听觉系统的常用物种。尽管老鼠在近中线处具有相当尖锐的辨别能力，但它们在声源位置的辨别方面表现出无能为力。我们测试了一个假设，即老鼠声音定位心理物理学的那些特征在其皮质神经元空间敏感性的特征中是明显的。此外，我们寻求皮质神经元活体空间敏感性的定量描述，以支持体外实验模型的发展，以研究空间听觉的皮质机制。我们评估了在麻醉的大鼠初级听觉皮层（A1）中单个和多个神经元反应的空间敏感性。在 360°的水平平面上，在神经阈值以上 10 到 40 dB 的水平上，在自由场噪声爆发中变化。在 A1 中遇到的所有神经元都表现出对大脑对侧半区的空间调谐，即它们对大脑对侧声源位置的反应强烈，对靠近额中线的位置反应急剧下降，对同侧的声源则反应较弱或没有反应。在 30 dB 的声级范围内，空间调谐非常稳定。与老鼠心理物理结果一致，对尖峰计数的线性判别分析表现出对近中线声音的高空间灵敏度和对离中线位置的差的辨别能力。半区空间调谐是之前测试的所有哺乳动物中最常见的模式。老鼠 A1 区中同质的神经元群体将成为研究该模式的基础机制的优秀系统。
