Division of Medical Sciences, Harvard University, Boston, Massachusetts 02115,
Department of Brain and Cognitive Sciences and McGovern Institute for Brain Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139.
J Neurosci. 2018 Sep 5;38(36):7870-7877. doi: 10.1523/JNEUROSCI.0484-18.2018. Epub 2018 Aug 13.
Neuroscience research has elucidated broad relationships between socioeconomic status (SES) and young children's brain structure, but there is little mechanistic knowledge about specific environmental factors that are associated with specific variation in brain structure. One environmental factor, early language exposure, predicts children's linguistic and cognitive skills and later academic achievement, but how language exposure relates to neuroanatomy is unknown. By measuring the real-world language exposure of young children (ages 4-6 years, 27 male/13 female), we confirmed the preregistered hypothesis that greater adult-child conversational experience, independent of SES and the sheer amount of adult speech, is related to stronger, more coherent white matter connectivity in the left arcuate and superior longitudinal fasciculi on average, and specifically near their anterior termination at Broca's area in left inferior frontal cortex. Fractional anisotropy of significant tract subregions mediated the relationship between conversational turns and children's language skills and indicated a neuroanatomical mechanism underlying the SES "language gap." whole-brain analyses revealed that language exposure was not related to any other white matter tracts, indicating the specificity of this relationship. Results suggest that the development of dorsal language tracts is environmentally influenced, specifically by early, dialogic interaction. Furthermore, these findings raise the possibility that early intervention programs aiming to ameliorate disadvantages in development due to family SES may focus on increasing children's conversational exposure to capitalize on the early neural plasticity underlying cognitive development. Over the last decade, cognitive neuroscience has highlighted the detrimental impact of disadvantaged backgrounds on young children's brain structure. However, to intervene effectively, we must know which proximal aspects of the environmental aspects are most strongly related to neural development. The present study finds that young children's real-world language exposure, and specifically the amount of adult-child conversation, correlates with the strength of connectivity in the left hemisphere white matter pathway connecting two canonical language regions, independent of socioeconomic status and the sheer volume of adult speech. These findings suggest that early intervention programs aiming to close the achievement gap may focus on increasing children's conversational exposure to capitalize on the early neural plasticity underlying cognitive development.
神经科学研究阐明了社会经济地位（SES）与幼儿大脑结构之间的广泛关系，但对于与大脑结构特定变化相关的特定环境因素的机制性知识知之甚少。一个环境因素，即早期语言暴露，预测了儿童的语言和认知技能以及以后的学业成就，但语言暴露如何与神经解剖学相关尚不清楚。通过测量幼儿（4-6 岁，27 名男性/13 名女性）的真实语言暴露，我们证实了预先注册的假设，即与 SES 无关，与成人言语的绝对数量相比，更多的成人与儿童的对话经验与左侧弓状束和上纵束的更强、更连贯的白质连通性相关，平均而言，特别是在左侧额下回的布罗卡区的前部终止处。显著束区的分数各向异性介导了对话回合与儿童语言技能之间的关系，并表明 SES“语言差距”背后存在神经解剖学机制。全脑分析表明，语言暴露与其他任何白质束都没有关系，表明这种关系具有特异性。研究结果表明，背侧语言束的发育受环境影响，特别是受早期对话互动的影响。此外，这些发现提出了一种可能性，即旨在通过家庭 SES 减轻发展劣势的早期干预计划可能侧重于增加儿童的对话暴露，以利用认知发展背后的早期神经可塑性。在过去的十年中，认知神经科学强调了不利背景对幼儿大脑结构的不利影响。然而，要进行有效的干预，我们必须知道环境方面的哪些近端方面与神经发育最密切相关。本研究发现，幼儿的真实世界语言暴露，特别是成人与儿童的对话量，与连接两个经典语言区域的左侧半球白质通路的连通强度相关，与社会经济地位和成人言语的绝对数量无关。这些发现表明，旨在缩小成就差距的早期干预计划可能侧重于增加儿童的对话暴露，以利用认知发展背后的早期神经可塑性。
