Gold J I, Knudsen E I
Department of Neurobiology, Stanford University, Stanford, California 94305-5125, USA.
J Neurophysiol. 2001 Apr;85(4):1575-84. doi: 10.1152/jn.2001.85.4.1575.
In the midbrain sound localization pathway of the barn owl, a map of auditory space is synthesized in the external nucleus of the inferior colliculus (ICX) and transmitted to the optic tectum. Early auditory experience shapes these maps of auditory space in part by modifying the tuning of the constituent neurons for interaural time difference (ITD), a primary cue for sound-source azimuth. Here we show that these adaptive modifications in ITD tuning correspond to changes in the pattern of connectivity within the inferior colliculus. We raised owls with an acoustic filtering device in one ear that caused frequency-dependent changes in sound timing and level. As reported previously, device rearing shifted the representation of ITD in the ICX and tectum but not in the primary source of input to the ICX, the central nucleus of the inferior colliculus (ICC). We applied the local anesthetic lidocaine (QX-314) iontophoretically in the ICC to inactivate small populations of neurons that represented particular values of frequency and ITD. We measured the effect of this inactivation in the optic tecta of a normal owl and owls raised with the device. In the normal owl, inactivation at a critical site in the ICC eliminated responses in the tectum to the frequency-specific ITD value represented at the site of inactivation in the ICC. The location of this site was consistent with the known pattern of ICC-ICX-tectum connectivity. In the device-reared owls, adaptive changes in the representation of ITD in the tectum corresponded to dramatic and predictable changes in the locations of the critical sites of inactivation in the ICC. Given that the abnormal representation of ITD in the tectum depended on frequency and was likely conveyed directly from the ICX, these results suggest that experience causes large-scale, frequency-specific adjustments in the pattern of connectivity between the ICC and the ICX.
在仓鸮的中脑声音定位通路中，听觉空间图谱在下丘外侧核（ICX）中合成，并传递至视顶盖。早期听觉经验部分地通过改变组成神经元对耳间时间差（ITD，一种声源方位的主要线索）的调谐来塑造这些听觉空间图谱。在这里，我们表明ITD调谐中的这些适应性改变与下丘内连接模式的变化相对应。我们用一个声学滤波装置饲养仓鸮，该装置会导致声音时间和强度随频率变化。如先前报道的那样，装置饲养使ICX和视顶盖中ITD的表征发生了偏移，但在下丘中央核（ICC），即ICX的主要输入源中却没有。我们通过离子电泳法将局部麻醉药利多卡因（QX - 314）应用于ICC，以灭活代表特定频率和ITD值的小群神经元。我们测量了这种灭活对正常仓鸮以及用该装置饲养的仓鸮的视顶盖的影响。在正常仓鸮中，ICC中一个关键部位的灭活消除了视顶盖对ICC中灭活部位所代表的频率特异性ITD值的反应。该部位的位置与已知的ICC - ICX - 视顶盖连接模式一致。在用装置饲养的仓鸮中，视顶盖中ITD表征的适应性变化与ICC中灭活关键部位位置的显著且可预测的变化相对应。鉴于视顶盖中ITD的异常表征取决于频率且可能直接从ICX传递而来，这些结果表明经验会导致ICC和ICX之间连接模式发生大规模的、频率特异性的调整。
