Oregon Hearing Research Center, Oregon Health and Science University, Portland, Oregon; and Biomedical Engineering Department, Johns Hopkins University, Baltimore, Maryland
Biomedical Engineering Department, Johns Hopkins University, Baltimore, Maryland.
J Neurophysiol. 2014 Jun 15;111(12):2624-33. doi: 10.1152/jn.00885.2013. Epub 2014 Mar 26.
Accurate sound localization is based on three acoustic cues (interaural time and intensity difference and spectral cues from directional filtering by the pinna). In natural listening conditions, every spatial position of a sound source provides a unique combination of these three cues in "natural alignment." Although neurons in the central nucleus (ICC) of the inferior colliculus (IC) are sensitive to multiple cues, they do not favor their natural spatial alignment. We tested for sensitivity to cue alignment in the nucleus of the brachium of the IC (BIN) in unanesthetized marmoset monkeys. The BIN receives its predominant auditory input from ICC and projects to the topographic auditory space map in the superior colliculus. Sound localization cues measured in each monkey were used to synthesize broadband stimuli with aligned and misaligned cues; spike responses to these stimuli were recorded in the BIN. We computed mutual information (MI) between the set of spike rates and the stimuli containing either aligned or misaligned cues. The results can be summarized as follows: 1) BIN neurons encode more information about auditory space when cues are aligned compared with misaligned. 2) Significantly more units prefer aligned cues in the BIN than in ICC. 3) An additive model based on summing the responses to stimuli with the localization cues varying individually accurately predicts the alignment preference with all cues varying. Overall, the results suggest that the BIN is the first site in the ascending mammalian auditory system that is tuned to natural combinations of sound localization cues.
精确的声音定位基于三个声学线索（两耳间时间和强度差异以及耳廓方向滤波的频谱线索）。在自然聆听条件下，声源的每个空间位置都提供了这三个线索的独特组合，呈现“自然对齐”。尽管下丘脑中核（ICN）的神经元对多个线索敏感，但它们并不偏爱其自然的空间对齐。我们在未麻醉的狨猴中测试了内臂核（BIN）对线索对齐的敏感性。BIN 主要接收来自 ICN 的听觉输入，并投射到上丘的拓扑听觉空间图。在每只猴子中测量的声音定位线索用于合成具有对齐和不对齐线索的宽带刺激；在 BIN 中记录对这些刺激的尖峰反应。我们计算了尖峰率集与包含对齐或不对齐线索的刺激之间的互信息（MI）。结果可以总结如下：1）当线索对齐时，BIN 神经元对听觉空间的编码信息更多。2）与 ICN 相比，BIN 中有更多的神经元更喜欢对齐的线索。3）基于对每个线索单独变化的刺激的响应求和的加法模型可以准确预测所有线索变化时的对齐偏好。总体而言，结果表明 BIN 是哺乳动物听觉系统中第一个对声音定位线索的自然组合进行调谐的部位。
