综述与专论: 鸣禽模型在语言学习中承担独特的生物学角色

鸣禽鸣唱与人类语言相似，是一种复杂的发声学习行为，并受脑中一组相互联系的神经核团调控。该组核团与人类发声控制相关脑区具有一定程度的结构同源性，并可能共享某些发声学习调控机制。因此，鸣禽成为研究发声学习神经机理的重要模式动物，不仅对鸟类语言学习，也可为揭示人类语言学习的神经过程和语言障碍的治疗提供重要参考借鉴。本文基于本课题组长期坚持的研究方向，较系统地概述了国内外鸣禽鸣唱行为研究的历史、重要发现和进展，及其为相关中枢神经系统疾病治疗带来的启示。     

中枢胆碱能系统投射支配鸣禽鸣唱控制系统并调控鸣唱行为

鸣禽因其独特的习得性鸣唱行为,成为了研究运动学习的理想模型。现已证实,鸣禽的鸣唱行为受前脑内的鸣唱控制系统直接调控。有证据显示,鸣唱控制系统内有胆碱能递质及其受体分布,其中发声运动核团接受来自基底前脑中枢胆碱能系统的胆碱能神经支配,其可通过胆碱能递质影响发声运动核团的神经活动,进而影响鸣唱行为。在哺乳动物中的研究证实,中枢胆碱能系统参与了对运动行为和运动学习神经过程的调控。了解中枢胆碱能系统对鸣禽鸣唱行为的调控作用,有助于更好地理解鸣禽鸣唱运动控制和鸣唱学习记忆的神经机制,并可从比较生理学的角度,为研究其它动物感觉运动和学习记忆的神经过程,乃至人类语言产生的神经过程提供重要参考。本文对迄今国内外在胆碱能递质对鸣禽发声运动核团作用受体的选择性及其对神经元活动影响的研究进展进行了综述,为揭示中枢胆碱能系统调控鸣禽鸣唱行为的神经机理提供有价值的线索。     

鸣禽端脑发声运动通路的电生理学特性

鸣禽是除了人类以外极少数具有发声信号学习能力的动物,其已成为研究运动序列控制和学习记忆神经过程的理想模型。鸣禽端脑中的高级发声中枢(high vocal center)、弓状皮质栎核(robust nucleus of the arcopallium)和脑干中的运动核团构成了控制发声的运动通路。该文对鸣禽端脑发声运动通路的电生理学特性及其在发声控制和鸣唱学习中的作用进行了全面的分析综述。     

鸟类的发声器官及其调控机制

鸟类是具有复杂声行为的动物,其拥有特殊的发声器官--鸣管.尽管鸣禽与非鸣禽的发声特性和发声器官解剖学差异较大,但是两者发声运动控制模式相似.文章综述了近年来鸟类鸣声研究的新进展,重点比较了鸣禽和非鸣禽发声器官的结构功能特点和发声特性调控的异同.作为一种动物模型,鸟类发声系统能为人类语言学习等研究提供借鉴.     

多巴胺系统调控鸣禽鸣唱相关神经核团及鸣唱行为

鸣禽的鸣唱与人类的语言产生相似,是一种复杂的习得性行为.因此,鸣禽可以作为研究人类语言学习与产生的重要模式动物.鸣禽鸣唱受到相互联系的鸣唱控制核团调控.多巴胺作为脑内重要的神经递质,参与调控哺乳动物多种活动.多巴胺及其受体在鸣禽鸣唱相关神经核团大量分布.近期研究表明,多巴胺通过调控鸣唱相关核团,促进鸣禽幼年期鸣曲学习、成年期鸣曲保持以及求偶性鸣唱的产生.本文结合本课题组的研究工作,对近年鸣禽多巴胺系统调控鸣唱相关神经核团及鸣唱行为的研究进展进行了综述,并提出了多巴胺信号调控鸣禽鸣唱学习行为的潜在机制.     

鸟类的发声系统和调控机制

鸟类是具有复杂声行为的动物,其拥有特殊的发声器官——鸣管。尽管鸣禽与非鸣禽的发声特性和发声器官解剖学差异较大,但是两者发声运动控制模式相似。文章综述了近年来鸟类呜声研究的新进展,重点比较了呜禽和非鸣禽发声器官的结构功能特点和发声特性调控的异同。作为一种动物模型,鸟类发声系统能为人类语言学习等研究提供借鉴。     

鸣禽前脑基底神经节X区与语言学习

成年鸣禽鸣唱语句的形成和维持依赖于听觉反馈。X区是鸣禽前脑回路的一个重要核团,对鸣禽的发声学习和语言结构的稳定有重要作用。X区在解剖结构、电生理学以及神经化学等方面的特性与哺乳类基底神经节极为相似。对鸣禽前脑X区的研究有助于揭示人类语言学习的中枢机制。本文对近年来鸣禽X区的相关研究进展,包括鸣禽X区的结构特征、电生理特性及神经化学特征予以阐述。     

鸣禽发声学习行为的神经生物学机制

鸣禽发声学习的控制系统主要由一条直接神经通路和一条辅助神经通路组成,由前脑控制发声学习的最高中枢ＨＶＣ、旁嗅叶的Ｘ区和巨细胞核外侧部（ｌＭＡＮ）组成的辅助通路,对鸟类发声学习行为的发育和调制具有重要作用。发声控制系统中神经元类型、数量及再生与更替、神经组构及其重组、神经介质和受体的分布等差异,决定了鸣禽在发声学习行为表现的差异以及性双态性。本文对近年鸟类控制发声学习行煌神经生物学机制的进展作了较为     

鸟鸣及其鸣唱控制系统发育可塑性研究进展

鸟类的鸣唱控制系统已成为研究神经系统与学习、行为和发育相关的一个重要模型。鸣禽鸣唱学习行为的神经基础为脊椎动物复杂习得行为的解剖学功能定位提供了一个范例。它也可为我们研究人类语言学习记忆提供借鉴,对近年来在鸟类鸣唱及其呜唱控制系统发育可塑性方面的研究进展进行了综述。     

致聋对鸣禽鸣唱行为的影响

鸣禽的鸣啭系统已是当今研究学习和记忆的重要模型。鸣禽的鸣啭学习包括2个阶段：感觉学习期和感觉-运动学习期,以及鸣唱运动和鸣唱学习2条通路。鸣禽的鸣唱行为依赖于听觉反馈系统,现已经证明致聋会使鸣曲结构发生变化,主要对近年来在致聋与鸣唱行为的影响及一些电生理变化研究方面进行介绍。     

Vocal Dueting and the Pair Bond

A possible mechanism is suggested that would link pair-specific dueting to pairbonding as an adaptive strategy. Working out a complex duet is interpreted as a kind of investment, more advantageous than other pre-mating investments and satisfying the partner's coyness.     

Vocal communication of simulated pain

While evidence suggests that pain cries produced by human babies and other mammal infants communicate pain intensity, whether the pain vocalisations of human adults also encode pain intensity, and which acoustic characteristics influence listeners’ perceptions, remains unexplored. Here, we investigated how trained actors communicated pain by comparing the acoustic characteristics of nonverbal vocalisations expressing different levels of pain intensity (mild, moderate and severe). We then performed playback experiments to examine whether vocalisers successfully communicated pain intensity to listeners, and which acoustic characteristics were responsible for variation in pain ratings. We found that the mean and range of voice fundamental frequency (F0, perceived as pitch), the amplitude of the vocalisation, the degree of periodicity of the vocalisation and the proportion of the signal displaying non-linear phenomena all increased with the level of simulated pain intensity. In turn, these parameters predicted increases in listeners’ ratings of pain intensity. We also found that while different voice features contributed to increases in pain ratings within each level of expressed pain, a combination of these features explained an impressive amount of the variance in listeners’ pain ratings, both across (76%) and within (31–54%) pain levels. Our results show that adult vocalisers can volitionally simulate and modulate pain vocalisations to influence listeners’ perceptions of pain in a manner consistent with authentic human infant and nonhuman mammal pain vocalisations, and highlight potential for the development of a practical quantitative tool to improve pain assessment in populations unable to self-report their subjective pain experience.     

Vocal attractiveness and voluntarily pitch-shifted voices

Previous studies have found that using software to pitch shift people's voices can boost their perceived attractiveness to opposite-sex adults: men prefer women's voices when pitch-shifted up, and women prefer men's voices when pitch-shifted down. In this study, we sought to determine whether speakers could affect their perceived vocal attractiveness by voluntarily shifting their own voices to reach specific target pitches (+20 Hz or −20 Hz, a pitch increment that is based on prior research). Two sets of Chinese college students participated in the research: 115 who served as speakers whose voices were recorded, and 167 who served as raters who evaluated the speakers' voices. We found that when female speakers increased their pitch they were judged as more attractive to both opposite-sex and same-sex raters. An additional unexpected finding was that male speakers tended to rate other males who shifted their voice up in pitch as more attractive. These findings suggest that voluntary pitch shifts can affect attractiveness, but that they do not fully match the patterns observed when pitch shifting is done digitally.     

Vocal communication in frogs

The robust nature of vocal communication in frogs has long attracted the attention of natural philosophers and their biologically inclined successors. Each frog species produces distinctive calls that facilitate pre-mating reproductive isolation and thus speciation. In many terrestrial species, a chorus of simultaneously calling males attracts females to breeding sites; reproductive females then choose and locate one male, using distinctive acoustic cues. Males compete with each other vocally and sometimes physically as well. Anuran acoustic signaling systems are thus subject to the strong pressures of sexual selection. We are beginning to understand the ways in which vocal signals are produced and decoded by the nervous system and the roles of neurally active hormones in both processes.     

Vocal Tract Morphology Determines Species-Specific Features in Vocal Signals of Lemurs (Eulemur)

The source-filter theory describes vocal production as a two-stage process involving the generation of a sound source, with its own spectral structure, which is then filtered by the resonant properties of the vocal tract. This theory has been successfully applied to the study of animal vocal signals since the 1990s. As an extension, models reproducing vocal tract resonance can be used to reproduce formant patterns and to understand the role of vocal tract filtering in nonhuman vocalizations. We studied three congeneric lemur species —Eulemur fulvus, E. macaco, E. rubriventer— using morphological measurements to build computational models of the vocal tract to estimate formants, and acoustic analysis to measure formants from natural calls. We focused on call types emitted through the nose, without apparent articulation. On the basis of anatomical measurements, we modeled the vocal tract of each species as a series of concatenated tubes, with a cross-sectional area that changed along the tract to approximate the morphology of the larynx, the nasopharyngeal cavity, the nasal chambers, and the nostrils. For each species, we calculated the resonance frequencies in 2500 randomly generated vocal tracts, in which we simulated intraspecific length and size variation. Formant location and spacing showed significant species-specific differences determined by the length of the vocal tract. We then measured formants of a set of nasal vocalizations (“grunts”) recorded from captive lemurs of the same species. We found species-specific differences in the natural calls. This is the first evidence that morphology of the vocal tract is relevant in generating filter-related acoustic cues that potentially provide receivers with information about the species of the emitter.