鸣禽鸣啭学习研究进展

禽的鸣啭表现出一种复杂的学习过程，鸣禽学习鸣啭的过程可以分为两个阶段．在感觉学习期，幼鸟必须听到成鸟的鸣啭，并形成鸣啭模板记忆；在感觉运动学习期，鸣禽通过听觉反馈与模板匹配逐步建立稳定的鸣啭．对近年来鸣禽鸣啭学习过程的研究进展进行综述．     

光声成像技术在鸣禽脑中的应用

鸣禽鸣啭学习与记忆机制的研究是当今神经科学领域的一个特色分支,近年来该研究迅猛发展.光声成像是一种新型无损脑功能成像技术.该文首次采用光声成像技术对鸣禽斑胸草雀脑进行研究,以期为揭示鸣禽鸣唱机制提供新的手段.     

鸣禽发声学习记忆的神经机制

鸣禽鸣啭控制系统已成为研究神经系统与学习记忆关系的重要模型.鸣啭系统在发育中所表现出的神经和行为变化的特点,为深入理解语言学习敏感期、突触联系的再分布、结构特化以及细胞死亡与神经发生机制提供了宝贵的信息.综述了国内外这一领域的研究进展.     

鸣禽前脑鸣啭控制核团内胆碱能神经元的分布

高级发声中枢（HVC）和古纹状体粗核（RA）是位于鸣禽前脑的两个主要鸣啭控制核团，以中国北方地区常见的两种鸣禽栗鹂（Emberiza rutila)和燕雀（Fingilla montifringilla）为材料，应用免疫组化方法，对两种鸣禽HVC和RA内胆碱能神经元的胞体大小和密度进行了观察、发现ChAT样免疫反应具有性别差异。这一结果提示胆碱能神经元可能在鸣啭的产生和学习过程中发挥着重要的作用。     

鸣禽鸣啭控制核团内GABA能神经元的分布研究

应用免疫组化方法对鸣禽粟鹀(Emberiza rutila)鸣啭控制核团内GABA能神经元的分布进行了研究，在高级发声中枢(HVC，high vocal center)，古纹状体粗核(RA，the robust nucleus of the archistrialum)，X区(Arca X)3个前脑核团内有GABA样免疫反应出现．HVC和RA中GABA能神经元胞体大小存在性别和季节间的差异．结果提示GABA能神经元可能参与了鸣禽鸣啭的产生和鸣啭学习。     

两种鸣禽鸣啭控制核团体积的季节性变化

用Ｎｉｓｓｌ染色和ＨＥ染色,通过定量分析研究了鸣禽粟巫和燕雀鸣啭控制核团体积的季节性变化,同时对睾丸体积的季节性变化进行了观察,结果表明,鸣禽前脑三个主要鸣啭相关核团上纹状体腹侧尾核,古纹状体粗核,旁嗅叶的Ｘ区的体积存在显著的季节性差异。睾丸的体积和重量亦呈显著的季节性变化,这些结果揭示,鸣禽鸣啭能力的季节性变化是受鸣啭控制核团体积和睾酮水平季节性变化的影响。     

界面核和高级发声中枢与鸣禽鸣曲的学习和维持

鸣禽鸣唱和人类语言都是经过后天学习而获得的。幼鸟在学习鸣唱时先记住教习曲模板，再通过发声反馈比较自鸣曲和模板并调整发声输出，成年后同样需要听觉反馈来维持自鸣曲的特征和稳定。因此，鸣禽听觉系统和运动系统对刺激的感觉运动整合过程是非常重要的。近年研究发现，感觉期幼鸟编码记忆模板的过程需要NIf-HVC投射的参与，同时这一突触联系与维持成年鸣禽可塑性鸣曲空间特征和鸣曲节律至关重要，其中，NMDAR、AchR和NE可能参与调节NIf-HVC突触的效能。HVC类似于人类的Broca区，而NIf类似于人类的Spt区，因此研究NIf-HVC突触在神经环路中的作用有助于揭示人类这两个脑区在语言形成中潜在的功能，有利于探索发声过程相关的感觉运动信息整合的机制     

栗鹀前脑发声控制核团体积的性别差异

栗鹀属于鸣禽类的一种,是东北常见的鸟类之一。本文对鸣禽栗鹀前脑发声核制核团HVc与RA进行了测量,并加以比较。结果表明,前脑HVc与RA核团体积存在着明显的性别差异。雄鸟的核团体积均大于雌鸟(P<0.05)。这表明造成栗鹀鸣啭能力的性别差异是由其神经结构的形态不同造成的。     

鸣禽鸟脑的季节可塑性

呜禽鸟的发声控制脑区具有明显的季节可塑性变化，它是鸣啭季节差异的神经基础．目前鸣禽成鸟的发声控制系统已成为研究中枢神经系统形态和功能可塑性的重要模型．本文着重就引起发声控制核团或脑区体积改变的诱导因素和触发体积改变的机制进行探讨．     

鸣禽前脑发声神经核团的神经元再生

神经元再生作为特有的发育现象,在成年鸣禽前脑中,由侧脑室壁区产生的细胞经过迁移、替换、分化到达前脑高级发声中枢和发声学习中枢,加入原有神经回路。鸣禽利用这些再生的神经元,参与发声,学习记忆的感知与运动过程,在人类脑损伤的修复机制方面给予借鉴和启示。     

Performance variability enables adaptive plasticity of 'crystallized' adult birdsong

Significant trial-by-trial variation persists even in the most practiced skills. One prevalent view is that such variation is simply 'noise' that the nervous system is unable to control or that remains below threshold for behavioural relevance. An alternative hypothesis is that such variation enables trial-and-error learning, in which the motor system generates variation and differentially retains behaviours that give rise to better outcomes. Here we test the latter possibility for adult bengalese finch song. Adult birdsong is a complex, learned motor skill that is produced in a highly stereotyped fashion from one rendition to the next. Nevertheless, there is subtle trial-by-trial variation even in stable, 'crystallized' adult song. We used a computerized system to monitor small natural variations in the pitch of targeted song elements and deliver real-time auditory disruption to a subset of those variations. Birds rapidly shifted the pitch of their vocalizations in an adaptive fashion to avoid disruption. These vocal changes were precisely restricted to the targeted features of song. Hence, birds were able to learn effectively by associating small variations in their vocal behaviour with differential outcomes. Such a process could help to maintain stable, learned song despite changes to the vocal control system arising from ageing or injury. More generally, our results suggest that residual variability in well learned skills is not entirely noise but rather reflects meaningful motor exploration that can support continuous learning and optimization of performance.     

Decrystallization of adult birdsong by perturbation of auditory feedback.

Young birds learn to sing by using auditory feedback to compare their own vocalizations to a memorized or innate song pattern; if they are deafened as juveniles, they will not develop normal songs. The completion of song development is called crystallization. After this stage, song shows little variation in its temporal or spectral properties. However, the mechanisms underlying this stability are largely unknown. Here we present evidence that auditory feedback is actively used in adulthood to maintain the stability of song structure. We found that perturbing auditory feedback during singing in adult zebra finches caused their song to deteriorate slowly. This 'decrystallization' consisted of a marked loss of the spectral and temporal stereotypy seen in crystallized song, including stuttering, creation, deletion and distortion of song syllables. After normal feedback was restored, these deviations gradually disappeared and the original song was recovered. Thus, adult birds that do not learn new songs nevertheless retain a significant amount of plasticity in the brain.     

How sleep affects the developmental learning of bird song

Sleep affects learning and development in humans and other animals, but the role of sleep in developmental learning has never been examined. Here we show the effects of night-sleep on song development in the zebra finch by recording and analysing the entire song ontogeny. During periods of rapid learning we observed a pronounced deterioration in song structure after night-sleep. The song regained structure after intense morning singing. Daily improvement in similarity to the tutored song occurred during the late phase of this morning recovery; little further improvement occurred thereafter. Furthermore, birds that showed stronger post-sleep deterioration during development achieved a better final imitation. The effect diminished with age. Our experiments showed that these oscillations were not a result of sleep inertia or lack of practice, indicating the possible involvement of an active process, perhaps neural song-replay during sleep. We suggest that these oscillations correspond to competing demands of plasticity and consolidation during learning, creating repeated opportunities to reshape previously learned motor skills.     

Contributions of an avian basal ganglia-forebrain circuit to real-time modulation of song

Cortical-basal ganglia circuits have a critical role in motor control and motor learning. In songbirds, the anterior forebrain pathway (AFP) is a basal ganglia-forebrain circuit required for song learning and adult vocal plasticity but not for production of learned song. Here, we investigate functional contributions of this circuit to the control of song, a complex, learned motor skill. We test the hypothesis that neural activity in the AFP of adult birds can direct moment-by-moment changes in the primary motor areas responsible for generating song. We show that song-triggered microstimulation in the output nucleus of the AFP induces acute and specific changes in learned parameters of song. Moreover, under both natural and experimental conditions, variability in the pattern of AFP activity is associated with variability in song structure. Finally, lesions of the output nucleus of the AFP prevent naturally occurring modulation of song variability. These findings demonstrate a previously unappreciated capacity of the AFP to direct real-time changes in song. More generally, they suggest that frontal cortical and basal ganglia areas may contribute to motor learning by biasing motor output towards desired targets or by introducing stochastic variability required for reinforcement learning.     

Projection neurons within a vocal motor pathway are born during song learning in zebra finches

Many birds learn song during a restricted 'sensitive' period. Juveniles memorize a song model, and then learn the pattern of muscle contractions necessary to reproduce the song. Of the neural changes accompanying avian song learning, perhaps the most remarkable is the production of new neurons which are inserted into the hyperstriatum ventralis pars caudalis (HVc), a region critical for song production. We report here that in young male zebra finches many of the new neurons incorporated into the HVc innervate the robust nucleus of the archistriatum (RA) which projects to motor neurons controlling the vocal musculature. Furthermore, far fewer of these new neurons are incorporated into the HVc of either adult males that are beyond the sensitive learning period, or young females (who do not develop song). Thus, a major portion of the vocal motor pathway is actually created during song learning. This may enable early sensory experience and vocal practice to not only modify existing neuronal circuits, but also shape the insertion and initial synaptic contacts of neurons controlling adult song.     

The role of sex steroids in the acquisition and production of birdsong

Male birdsong is generally regarded as a secondary sexual characteristic under the control of gonadal steroids. Song typically waxes and wanes with the seasonal cycle of testicular growth and regression and decreases after adult castration. Testosterone therapy reinstates song, induces it in females, augments it in intact males, and spring testosterone profiles correlate with seasonal song production. Thus, testosterone has been viewed as a major factor in song acquisition and production acting either directly, or after aromatization within the brain. We show here, however, that song learning and early phases of the development of singing both take place in castrated male birds with no significant levels of testosterone in their blood plasma. Testosterone seems to be required for song crystallization, however. Oestradiol was unexpectedly still present after castration, evidently from a non-testicular source, throughout the period of male song acquisition.     

Female visual displays affect the development of male song in the cowbird

The role of social stimulation in avian vocal learning is well documented. The separate contribution of social, as opposed to vocal, stimulation has been difficult to address, however, because in almost all cases both tutor and pupil sing. The opportunity to isolate such effects arose in cowbirds (Molothrus ater ater) after discovering that males housed with non-singing female cowbirds made vocal changes which related directly to the female preferences for native song. Here we report how females communicate with males about songs. We describe a visual display by females, a wing stroke, that is elicited by specific vocalizations. The songs that trigger wing strokes are in turn highly effective releasers of copulatory postures, and thus this previously unnoticed female display has biological significance. The data not only provide the first evidence of the tutorial role of male-female interactions during song ontogeny, they also clearly implicate visual stimulation in song learning, a process that has until now been assumed to be affected only by auditory information.     

Learned kin recognition cues in a social bird

In many cooperatively breeding birds, kin selection has an important role in the evolution and maintenance of social behaviour, and 'helpers' can maximize indirect fitness gains by preferentially allocating care to close relatives. Although there is evidence for kin-biased helping behaviour in several species, the mechanism of kin recognition underlying this behaviour is poorly understood. Vocalizations are the most commonly used cues in avian recognition systems, but the effectiveness of vocal signals as reliable recognition cues must depend on how they are acquired. However, there have been no experimental studies of the development of vocal recognition cues in cooperative birds; indeed, the ontogeny of all bird vocalizations other than song is poorly known in any species. Here, we show that cooperatively breeding long-tailed tits (Aegithalos caudatus) can discriminate between kin and non-kin according to the individual-specific characteristics of contact calls, and show experimentally that individuals learn these calls from provisioning adults during the nestling period. Finally, we show that the pattern of cooperative behaviour in this species is consistent with the use of recognition cues learned through association.     

英文歌曲教学与英语口语的提高

将音乐引入课堂,运用正确的方法来学唱英文歌曲,有助于激发学生的学习英语的兴趣,增强学好英语的信心,提供练习英语口语的机会。