Keller Georg B, Hahnloser Richard H R
Institute of Neuroinformatics, University of Zurich/ETH Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
Nature. 2009 Jan 8;457(7226):187-90. doi: 10.1038/nature07467. Epub 2008 Nov 12.
Songbirds are capable of vocal learning and communication and are ideally suited to the study of neural mechanisms of complex sensory and motor processing. Vocal communication in a noisy bird colony and vocal learning of a specific song template both require the ability to monitor auditory feedback to distinguish self-generated vocalizations from external sounds and to identify mismatches between the developing song and a memorized template acquired from a tutor. However, neurons that respond to auditory feedback from vocal output have not been found in song-control areas despite intensive searching. Here we investigate feedback processing outside the traditional song system, in single auditory forebrain neurons of juvenile zebra finches that were in a late developmental stage of song learning. Overall, we found similarity of spike responses during singing and during playback of the bird's own song, with song responses commonly leading by a few milliseconds. However, brief time-locked acoustic perturbations of auditory feedback revealed complex sensitivity that could not be predicted from passive playback responses. Some neurons that responded to playback perturbations did not respond to song perturbations, which is reminiscent of sensory-motor mirror neurons. By contrast, some neurons were highly feedback sensitive in that they responded vigorously to song perturbations, but not to unperturbed songs or perturbed playback. These findings suggest that a computational function of forebrain auditory areas may be to detect errors between actual feedback and mirrored feedback deriving from an internal model of the bird's own song or that of its tutor. Such feedback-sensitive spikes could constitute the key signals that trigger adaptive motor responses to song disruptions or reinforce exploratory motor gestures for vocal learning.
鸣禽具备发声学习和交流的能力，非常适合用于研究复杂感觉和运动处理的神经机制。在嘈杂的鸟群中进行发声交流以及学习特定的歌曲模板，都需要具备监测听觉反馈的能力，以便将自身发出的声音与外部声音区分开来，并识别发育中的歌声与从导师那里习得并记忆的模板之间的不匹配之处。然而，尽管进行了深入搜索，在歌曲控制区域中尚未发现对发声输出的听觉反馈做出反应的神经元。在此，我们研究了传统歌曲系统之外的反馈处理过程，研究对象是处于歌曲学习后期发育阶段的幼年斑胸草雀的单个听觉前脑神经元。总体而言，我们发现鸟类在唱歌期间和播放自己的歌曲期间的尖峰反应具有相似性，歌曲反应通常会提前几毫秒出现。然而，听觉反馈的短暂时间锁定声学扰动揭示了复杂的敏感性，这无法从被动播放反应中预测出来。一些对播放扰动做出反应的神经元对歌曲扰动没有反应，这让人联想到感觉运动镜像神经元。相比之下，一些神经元对反馈高度敏感，因为它们对歌曲扰动反应强烈，但对未受扰动的歌曲或受扰动的播放没有反应。这些发现表明，前脑听觉区域的一种计算功能可能是检测实际反馈与源自鸟类自身歌曲或其导师歌曲内部模型的镜像反馈之间的误差。这种对反馈敏感的尖峰可能构成关键信号，触发对歌曲干扰的适应性运动反应，或加强用于发声学习的探索性运动姿态。
