Biomedical Engineering Department, Johns Hopkins University, Baltimore, Maryland 21205, USA.
J Neurosci. 2013 Feb 27;33(9):3891-904. doi: 10.1523/JNEUROSCI.3437-12.2013.
The spatial location of sounds is an important aspect of auditory perception, but the ways in which space is represented are not fully understood. No space map has been found within the primary auditory pathway. However, a space map has been found in the nucleus of the brachium of the inferior colliculus (BIN), which provides a major auditory projection to the superior colliculus. We measured the spectral processing underlying auditory spatial tuning in the BIN of unanesthetized marmoset monkeys. Because neurons in the BIN respond poorly to tones and are broadly tuned, we used a broadband stimulus with random spectral shapes (RSSs) from which both spatial receptive fields and frequency sensitivity can be derived. Responses to virtual space (VS) stimuli, based on the animal's own ear acoustics, were compared with the predictions of a weight-function model of responses to the RSS stimuli. First-order (linear) weight functions had broad spectral tuning (approximately three octaves) and were excitatory in the contralateral ear, inhibitory in the ipsilateral ear, and biased toward high frequencies. Responses to interaural time differences and spectral cues were relatively weak. In cross-validation tests, the first-order RSS model accurately predicted the measured VS tuning curves in the majority of neurons, but was inaccurate in 25% of neurons. In some cases, second-order weighting functions led to significant improvements. Finally, we found a significant correlation between the degree of binaural weight asymmetry and the best azimuth. Overall, the results suggest that linear processing of interaural level difference underlies spatial tuning in the BIN.
声音的空间位置是听觉感知的一个重要方面，但空间的表示方式还不完全清楚。在初级听觉通路上没有发现空间图谱。然而，在桥脑臂核（BIN）中发现了一个空间图谱，该核为上丘提供了主要的听觉投射。我们测量了未麻醉的狨猴 BIN 中听觉空间调谐的光谱处理。由于 BIN 中的神经元对音调的反应很差，并且具有广泛的调谐，因此我们使用了具有随机光谱形状的宽带刺激（RSS），从中可以得出空间感受野和频率敏感性。基于动物自身耳朵声学的虚拟空间（VS）刺激的反应与 RSS 刺激反应的权重函数模型的预测进行了比较。一阶（线性）权重函数具有广泛的光谱调谐（约三个八度），在对侧耳中为兴奋性，在同侧耳中为抑制性，偏向高频。对两耳时间差和光谱线索的反应相对较弱。在交叉验证测试中，一阶 RSS 模型准确地预测了大多数神经元的测量 VS 调谐曲线，但在 25%的神经元中不准确。在某些情况下，二阶加权函数会导致显著改善。最后，我们发现双侧权重不对称的程度与最佳方位之间存在显著相关性。总的来说，结果表明，BIN 中的空间调谐是基于两耳水平差的线性处理。
