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说，但人类说话能力的神经生物学起源仍然鲜为人知。研究表明，纹状体--一种与大脑皮层形成复杂连接的皮质下结构--可能在发声学习的进化中起着重要作用。发声学习是根据社会经验修改发声方式的能力，而发声学习是发育过程中获得语音所必需的。纹状体也是FOXP2基因表达的关键部位，FOXP2基因在现代人中经历了正向选择，并以突变的形式导致了一种影响语言产生的遗传性疾病。然而，到目前为止，表明纹状体在言语和语言进化中发挥作用的证据主要来自实验物种，如鸟类和老鼠，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，乔治华盛顿大学博士生瑟琳娜·比安奇目前的项目目的是识别非人类灵长类纹状体的神经特征，这些特征可能与人类语音特征的发声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和分子分析来检查圈养黑猩猩的纹状体，已经记录了为吸引实验者的注意而使用习得的、自愿控制的发声(引起注意的发声)的情况。具体目标包括评估产生注意发声的黑猩猩的纹状体是否与没有这种发声表型的黑猩猩在1)形态以及与大脑皮层运动和语言相关区域的连接模式方面的不同；以及2)神经元的可塑性和与突触功能和FOXP2相关的蛋白质的表达。在进化上接近人类的动物模型中研究发声交流的神经生物学，可能有助于在达尔文的语言起源框架内识别语言产生的前体，即非人类灵长类大脑中现有神经结构的遗传和修改。作为该项目的一部分，将通过与史密森国家自然历史博物馆的推广计划以及开发在线资源和教材来促进关于大脑和语言进化的知识的传播。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.