Chase Steven M, Young Eric D
Center for Hearing Sciences, Department of Biomedical Engineering, Johns Hopkins University, Baltimore, Maryland 21205, USA.
J Neurosci. 2005 Aug 17;25(33):7575-85. doi: 10.1523/JNEUROSCI.0915-05.2005.
The auditory system uses three cues to decode sound location: interaural time differences (ITDs), interaural level differences (ILDs), and spectral notches (SNs). Initial processing of these cues is done in separate brainstem nuclei, with ITDs in the medial superior olive, ILDs in the lateral superior olive, and SNs in the dorsal cochlear nucleus. This work addresses the nature of the convergence of localization information in the central nucleus of the inferior colliculus (ICC). Ramachandran et al. (1999) argued that ICC neurons of types V, I, and O, respectively, receive their predominant inputs from ITD-, ILD-, and SN-sensitive brainstem nuclei, suggesting that these ICC response types should be differentially sensitive to localization cues. Here, single-unit responses to simultaneous manipulation of pairs of localization cues were recorded, and the mutual information between discharge rate and individual cues was quantified. Although rate responses to cue variation were generally consistent with those expected from the hypothesized anatomical connections, the differences in information were not as large as expected. Type I units provide the most information, especially about SNs in the physiologically useful range. Type I and O units provide information about ILDs, even at low frequencies at which actual ILDs are very small. ITD information is provided by a subset of all low-frequency neurons. Type V neurons provide information mainly about ITDs and the average binaural intensity. These results are the first to quantify the relative representation of cues in terms of information and suggest a variety of degrees of cue integration in the ICC.
耳间时间差(ITD)、耳间声级差(ILD)和频谱凹陷(SN)。这些线索的初始处理在脑干的不同核团中进行,ITD由内侧上橄榄核处理,ILD由外侧上橄榄核处理,SN由蜗背侧核处理。这项研究探讨了下丘中央核(ICC)中定位信息汇聚的本质。Ramachandran等人(1999年)认为,V型、I型和O型的ICC神经元分别主要从对ITD、ILD和SN敏感的脑干核团接收输入,这表明这些ICC反应类型对定位线索应具有不同的敏感性。在此,记录了对成对定位线索同时进行操作时的单神经元反应,并对放电率与各个线索之间的互信息进行了量化。尽管对线索变化的速率反应通常与假设的解剖学连接所预期的一致,但信息差异并不像预期的那么大。I型神经元提供的信息最多,尤其是在生理有用范围内关于SN的信息。I型和O型神经元提供关于ILD的信息,即使在实际ILD非常小的低频情况下也是如此。ITD信息由所有低频神经元的一个子集提供。V型神经元主要提供关于ITD和双耳平均强度的信息。这些结果首次从信息角度量化了线索的相对表征,并表明ICC中存在多种程度的线索整合。