Seidl Armin H, Grothe Benedikt
Max Planck Institute of Neurobiology, D-82152 Martinsried, Germany
J Neurophysiol. 2005 Aug;94(2):1028-36. doi: 10.1152/jn.01143.2004. Epub 2005 Apr 13.
Sound localization is one of the most important tasks performed by the auditory system. Differences in the arrival time of sound at the two ears are the main cue to localize low-frequency sound in the azimuth. In the mammalian brain, such interaural time differences (ITDs) are encoded in the auditory brain stem; first by the medial superior olive (MSO) and then transferred to higher centers, such as the dorsal nucleus of the lateral lemniscus (DNLL), a brain stem nucleus that gets a direct input from the MSO. Here we demonstrate for the first time that ITD sensitivity in gerbils undergoes a developmental maturation after hearing onset. We further show that this development can be disrupted by altering the animal's acoustic experience during a critical period. In animals that had been exposed to omnidirectional white noise during a restricted time period right after hearing onset, ITD tuning did not develop normally. Instead, it was similar to that of juvenile animals 3 days after hearing onset, with the ITD functions not adjusted to the physiological range. Animals that had been exposed to omnidirectional noise as adults did not show equivalent abnormal ITD tuning. The development presented here is in contrast to that of the development of neuronal representation of ITDs in the midbrain of barn owls and interaural intensity differences in ferrets, where the representations are adjusted by an interaction of auditory and visual inputs. The development of ITD tuning presented here most likely depends on normal acoustic experience and may be related to the maturation of inhibitory inputs to the ITD detector itself.
声音定位是听觉系统执行的最重要任务之一。声音到达双耳的时间差异是在方位上定位低频声音的主要线索。在哺乳动物大脑中，这种双耳时间差异（ITD）在听觉脑干中进行编码；首先由内侧上橄榄核（MSO）编码，然后传递到更高的中枢，如外侧丘系背核（DNLL），这是一个直接从MSO接收输入的脑干核团。在这里，我们首次证明沙鼠的ITD敏感性在听力开始后经历发育成熟。我们进一步表明，在关键期改变动物的声学体验会破坏这种发育。在听力开始后紧接着的一段受限时间内暴露于全向白噪声的动物中，ITD调谐没有正常发育。相反，它类似于听力开始后3天的幼年动物，ITD功能未调整到生理范围。成年后暴露于全向噪声的动物没有表现出同等的异常ITD调谐。这里呈现的发育与仓鸮中脑ITD的神经元表征以及雪貂双耳强度差异的发育形成对比，在那里表征通过听觉和视觉输入的相互作用进行调整。这里呈现的ITD调谐发育很可能依赖于正常的声学体验，并且可能与ITD探测器本身抑制性输入的成熟有关。
