Doctoral Dissertation Research: The striatum in the evolution of flexibile, learned vocal communication

尽管有许多关于语言进化的假设，但人类说话能力的神经生物学起源仍然知之甚少。研究表明，纹状体是一种与大脑皮层形成复杂联系的皮质下结构，可能在发声学习的进化中很重要--发声学习是根据社会经验改变发声的能力--这是在发育过程中获得言语所必需的。纹状体也是FOXP 2表达的关键部位，FOXP 2是一种在现代人类中经历正选择的基因，并且以突变的形式负责影响语言产生的遗传性疾病。然而，迄今为止，表明纹状体在言语和语言进化中的作用的证据主要来自实验物种，如鸟类和小鼠，它们在进化上与人类相距甚远。在切特舍伍德博士的指导下，博士生塞丽娜比安奇（乔治华盛顿大学）目前的项目的目的是确定非人类灵长类动物纹状体的神经特征，这些特征可能与人类语音特征的语音学习能力的进化有关。为此，该项目使用非侵入性神经成像技术，以及死后组织学和分子分析，检查圈养黑猩猩的纹状体，其中使用学习，自愿控制发声，以吸引实验者的注意力（引起注意的发声）已被记录。具体目标包括评估产生引起注意的发声的黑猩猩的纹状体是否与不表现出这种发声表型的黑猩猩在1）形态学上不同，以及与大脑皮层的运动和语言相关区域的连接模式;和2）神经元可塑性和与突触功能和FOXP 2相关的蛋白质的表达。在进化上接近人类的动物模型中调查语音交流的神经生物学可能有助于在达尔文的语言起源框架内识别语音产生的前体，作为非人类灵长类动物大脑中现有神经结构的“修改”。作为该项目的一部分，将通过与史密森尼国家自然历史博物馆的外联方案合作，以及开发在线资源和教材，促进传播有关大脑和语言进化的知识。此外，该项目创建的组织学收藏将提供给其他研究人员。

Despite numerous hypotheses concerning language evolution, the neurobiological origins of the human capacity to speak remain little understood. Studies suggest that the striatum, a subcortical structure forming complex connections with the cerebral cortex, may be important in the evolution of vocal learning - the capacity to modify vocalizations in response to social experience - which is necessary to acquire speech during development. The striatum also is a key site of expression of FOXP2, a gene that underwent positive selection in modern humans, and, in a mutated form, is responsible for a hereditary disorder affecting language production. To date, however, evidence indicating a role of the striatum in the evolution of speech and language mainly comes from experimental species, such as birds and mice, which are evolutionarily distant from humans. The aim of the current project by doctoral student Serena Bianchi (George Washington University), under the guidance of Dr. Chet Sherwood, is to identify neural features of the non-human primate striatum that may have been associated with the evolution of the capacity for vocal learning that characterizes human speech. To this end, this project uses non-invasive neuroimaging techniques, and post-mortem histological and molecular analyses, to examine the striatum of captive chimpanzees for which the use of learned, voluntarily controlled vocalizations produced to attract the attention of the experimenter (attention-getting vocalizations) has been documented. Specific aims include assessing whether the striatum of chimpanzees who produce attention-getting vocalizations differs from chimpanzees that do not exhibit this vocal phenotype in 1) morphology, and pattern of connections with motor and language-related regions of the cerebral cortex; and 2) neuronal plasticity and expression of proteins associated with synaptic functions and FOXP2. Investigating the neurobiology of vocal communication in an animal model evolutionarily close to humans may help identify precursors to speech production within a Darwinian framework of language origins as 'descent with modifications' of existing neural structures in the non-human primate brain. As part of this project, dissemination of knowledge about the evolution of the brain and language will be fostered through collaboration with the outreach program of the Smithsonian National Museum of Natural History, and the development of on-line resources and teaching materials. In addition, the histological collection created by this project will be made available to other researchers.