Chase Steven M, Young Eric D
Center for Hearing Sciences, Department of Biomedical Engineering, Johns Hopkins University, Baltimore, Maryland 21205, USA.
J Neurosci. 2006 Apr 12;26(15):3889-98. doi: 10.1523/JNEUROSCI.4986-05.2006.
To preserve multiple streams of independent information that converge onto a neuron, the information must be re-represented more efficiently in the neural response. Here we analyze the increase in the representational capacity of spike timing over rate codes using sound localization cues as an example. The inferior colliculus receives convergent input from multiple auditory brainstem nuclei, including sound localization information such as interaural level differences (ILDs), interaural timing differences (ITDs), and spectral cues. Virtual space techniques were used to create stimulus sets varying in two sound-localization parameters each. Information about the cues was quantified using a spike distance metric that allows one to separate contributions to the information arising from spike rate and spike timing. Spike timing enhances the representation of spectral and ILD cues at timescales averaging 12 ms. ITD information, however, is carried by a rate code. Comparing responses to frozen and random noise shows that the temporal information is mainly attributable to phase locking to temporal stimulus features, with an additional first-spike latency component. With rate-based codes, there is significant confounding of information about two cues presented simultaneously, meaning that the cues cannot be decoded independently. Spike-timing-based codes reduce this confounded information. Furthermore, the relative representation of the cues often changes as a function of the time resolution of the code, implying that information about multiple cues can be multiplexed onto individual spike trains.
为了保留汇聚到单个神经元上的多个独立信息流，这些信息必须在神经反应中以更高效的方式重新呈现。在此，我们以声音定位线索为例，分析尖峰时间相对于发放率编码在表征能力上的提升。下丘从多个听觉脑干核接收汇聚输入，包括诸如耳间声级差（ILD）、耳间时间差（ITD）和频谱线索等声音定位信息。利用虚拟空间技术创建了在两个声音定位参数上各自变化的刺激集。关于这些线索的信息使用尖峰距离度量进行量化，该度量允许区分尖峰发放率和尖峰时间对信息的贡献。尖峰时间在平均12毫秒的时间尺度上增强了频谱和ILD线索的表征。然而，ITD信息由发放率编码携带。比较对冻结噪声和随机噪声的反应表明，时间信息主要归因于对时间刺激特征的锁相，还有一个额外的首个尖峰潜伏期成分。对于基于发放率的编码，同时呈现的两个线索的信息存在显著混淆，这意味着这些线索无法被独立解码。基于尖峰时间的编码减少了这种混淆信息。此外，线索的相对表征常常随编码的时间分辨率而变化，这意味着关于多个线索的信息可以被复用在单个尖峰序列上。
