Cluster of Excellence "Hearing4all", Department for Neuroscience, University of Oldenburg, Oldenburg, Germany.
Department of Biology, Humboldt-Universität zu Berlin, Berlin, Germany.
PLoS Biol. 2015 Mar 11;13(3):e1002096. doi: 10.1371/journal.pbio.1002096. eCollection 2015 Mar.
The senses of animals are confronted with changing environments and different contexts. Neural adaptation is one important tool to adjust sensitivity to varying intensity ranges. For instance, in a quiet night outdoors, our hearing is more sensitive than when we are confronted with the plurality of sounds in a large city during the day. However, adaptation also removes available information on absolute sound levels and may thus cause ambiguity. Experimental data on the trade-off between benefits and loss through adaptation is scarce and very few mechanisms have been proposed to resolve it. We present an example where adaptation is beneficial for one task--namely, the reliable encoding of the pattern of an acoustic signal-but detrimental for another--the localization of the same acoustic stimulus. With a combination of neurophysiological data, modeling, and behavioral tests, we show that adaptation in the periphery of the auditory pathway of grasshoppers enables intensity-invariant coding of amplitude modulations, but at the same time, degrades information available for sound localization. We demonstrate how focusing the response of localization neurons to the onset of relevant signals separates processing of localization and pattern information temporally. In this way, the ambiguity of adaptive coding can be circumvented and both absolute and relative levels can be processed using the same set of peripheral neurons.
动物的感觉器官面临着不断变化的环境和不同的背景。神经适应是调整对不同强度范围的敏感性的一个重要工具。例如，在一个安静的夜晚，我们的听觉比白天在大城市中面对众多声音时更为敏感。然而，适应也会消除有关绝对声音水平的可用信息，从而可能导致歧义。关于适应过程中权衡利弊的实验数据很少，并且提出的机制很少能够解决这个问题。我们提出了一个例子，其中适应对一项任务是有益的——即可靠地编码声信号的模式——但对另一项任务则是有害的——即定位相同的声刺激。通过神经生理学数据、建模和行为测试的组合，我们表明，在蝗虫听觉通路的外围，适应可以实现幅度调制的强度不变编码，但同时，会降低用于声音定位的可用信息。我们展示了如何使定位神经元对相关信号的起始的反应集中，从而在时间上分离定位和模式信息的处理。通过这种方式，可以避免自适应编码的歧义，并且可以使用同一组外围神经元来处理绝对和相对水平。
