Functional Contributions of the Arcuate Fasciculus to Language Processing.

Functional Contributions of the Arcuate Fasciculus to Language Processing.

Current evidence strongly suggests that the arcuate fasciculus (AF) is critical for language, from spontaneous speech and word retrieval to repetition and comprehension abilities. However, to further pinpoint its unique and differential role in language, its anatomy needs to be explored in greater detail and its contribution to language processing beyond that of known cortical language areas must be established. We address this in a comprehensive evaluation of the specific functional role of the AF in a well-characterized cohort of individuals with chronic aphasia (n = 33) following left hemisphere stroke. To evaluate macro- and microstructural integrity of the AF, tractography based on the constrained spherical deconvolution model was performed. The AF in the left and right hemispheres were then manually reconstructed using a modified 3-segment model, and a modified 2-segment model. The normalized volume and a measure of microstructural integrity of the long and the posterior segments of the AF were significantly correlated with language indices while controlling for gender and lesion volume. Specific contributions of AF segments to language while accounting for the role of specific cortical language areas – inferior frontal, inferior parietal, and posterior temporal – were tested using multiple regression analyses. Involvement of the following tract segments in the left hemisphere in language processing beyond the contribution of cortical areas was demonstrated: the long segment of the AF contributed to naming abilities; anterior segment – to fluency and naming; the posterior segment – to comprehension. The results highlight the important contributions of the AF fiber pathways to language impairments beyond that of known cortical language areas. At the same time, no clear role of the right hemisphere AF tracts in language processing could be ascertained. In sum, our findings lend support to the broader role of the left AF in language processing, with particular emphasis on comprehension and naming, and point to the posterior segment of this tract as being most crucial for supporting residual language abilities.

当前证据有力地表明，弓状束（AF）对语言至关重要，从自发言语、词汇检索到重复和理解能力均是如此。然而，为了进一步明确它在语言中独特且有差异的作用，需要更详细地探究其解剖结构，并且必须确定它在已知皮质语言区域之外对语言处理的贡献。我们在对一组特征明确的左侧半球卒中后慢性失语症患者（n = 33）进行的综合评估中探讨了这一问题。为了评估弓状束的宏观和微观结构完整性，基于约束球形反卷积模型进行了纤维束成像。然后使用改良的3段模型和改良的2段模型对左右半球的弓状束进行手动重建。在控制性别和病变体积的情况下，弓状束长段和后段的标准化体积以及微观结构完整性的测量值与语言指标显著相关。使用多元回归分析测试了弓状束各段在考虑特定皮质语言区域（额下回、顶下小叶和颞后回）作用的情况下对语言的特定贡献。研究表明，在皮质区域贡献之外，左侧半球以下纤维束段参与语言处理：弓状束长段对命名能力有贡献；前段对流畅性和命名有贡献；后段对理解有贡献。结果凸显了弓状束纤维通路在已知皮质语言区域之外对语言障碍的重要贡献。同时，无法确定右侧半球弓状束在语言处理中的明确作用。总之，我们的研究结果支持左侧弓状束在语言处理中更广泛的作用，尤其强调理解和命名，并指出该纤维束的后段对支持残余语言能力最为关键。