Organismic and Evolutionary Biology, University of Massachusetts Amherst, Amherst, MA, USA.
Center for Neuroendocrine Studies, University of Massachusetts Amherst, Amherst, MA, USA.
Dev Neurobiol. 2021 Mar;81(2):123-138. doi: 10.1002/dneu.22802. Epub 2021 Jan 29.
Encoding of conspecific signals during development can reinforce species barriers as well as set the stage for learning and production of species-typical vocalizations. In altricial songbirds, the development of the auditory system is not complete at hatching, so it is unknown the degree to which recently hatched young can process auditory signals like birdsong. We measured in vivo extracellular responses to song stimuli in a zebra finch (Taeniopygia guttata) secondary auditory forebrain region, the caudomedial nidopallium (NCM). We recorded from three age groups between 13 days post-hatch and adult to identify possible shifts in stimulus encoding that occur before the opening of the sensitive period of song motor learning. We did not find differences in putative cell type composition, firing rate, response strength, and selectivity across ages. Across ages narrow-spiking units had higher firing rates, response strength, accuracy, and trial-by-trial reliability along with lower selectivity than broad-spiking units. In addition, we showed that stimulus-specific adaptation, a characteristic of adult NCM, was also present in nestlings and fledglings. These results indicate that most features of secondary auditory processing are already adult-like shortly after hatching. Furthermore, we showed that selectivity for species-specific stimuli is similar across all ages, with the greatest fidelity in temporal coding in response to conspecific song and domesticated Bengalese finch song, and reduced fidelity in response to owl finch song, a more ecologically relevant heterospecific, and white noise. Our study provides the first evidence that the electrophysiological properties of higher-order auditory neurons are already mature in nestling songbirds.
在发育过程中对同种信号进行编码不仅可以加强物种之间的障碍，还可以为学习和产生物种典型的发声奠定基础。在晚成鸟类中，听觉系统在孵化时并未完全发育，因此尚不清楚刚孵化的幼鸟在多大程度上能够像鸟类一样处理听觉信号。我们在斑胸草雀（Taeniopygia guttata）的次级听觉前脑区域即尾侧中脑背核（NCM）中测量了对歌曲刺激的活体细胞外反应。我们记录了孵化后 13 天至成年的三个年龄组的反应，以确定在鸣禽运动学习敏感期开放之前可能发生的刺激编码变化。我们没有发现不同年龄组之间假定的细胞类型组成、放电率、反应强度和选择性有差异。在所有年龄组中，窄峰放电单位的放电率、反应强度、准确性和逐次试验的可靠性均高于宽峰放电单位，而选择性则低于宽峰放电单位。此外，我们还表明，刺激特异性适应是成年 NCM 的特征，在雏鸟和幼鸟中也存在。这些结果表明，在孵化后不久，次级听觉处理的大多数特征已经类似于成年鸟类。此外，我们还表明，对物种特异性刺激的选择性在所有年龄段都相似，对同种鸣禽和驯化的虎皮鹦鹉鸣曲的反应具有最大的时间编码保真度，而对猫头鹰雀鸣曲的反应保真度降低，对更具生态相关性的异源种和白噪声的反应保真度降低。我们的研究首次提供了证据，表明在巢雏鸣禽中，高级听觉神经元的电生理特性已经成熟。
