腦部連結與句法處理能力側化的關係

Abstract

過去研究認為語言處理能力有左側化的傾向，其中以句法處理能力最為左側化。但語言功能性側化背後的腦部神經機制則尚未有定論，本研究以分視野 (Split Visual Field Paradigm) 的方式呈現中文詞組結合成的片語為媒介，並結合三種不同類型的測量工具 — 事件關聯電位(Event-Related Potential, ERP)、擴散磁振造影(Diffusion Tensor Imaging, DTI)、靜息狀態功能性磁振造影(Resting-state Functional Magnetic Resonance Imaging, RS-fMRI)，更全面地從處理句法時的即時腦部功能性反應、腦部白質徑結構密度、腦部靜息態的功能性連結，來探討健康的年輕人中，腦部結構性與功能性連結與側化的句法處理能力之間的關聯。 本研究包括24位慣用右手且家族史也皆為右利手的年輕人，所有受試者們皆在七個月內進行了三個部分的實驗 — 實驗一是ERP腦波實驗，實驗二與三則是DTI腦部結構與RS-fMRI靜態功能造影。實驗ㄧ過程中，受試者將先閱讀呈現在視野中央的語詞，然後閱讀出現在左或右視野的目標詞後，判斷片語通順與否，在這當中同時利用腦波紀錄右腦和左腦優勢處理句法錯誤的歷程，如同先前研究，我們發現句法處理的效果(P600 grammaticality effect)側化至左腦。實驗二與三的過程中，受試者平躺靜止，以得到腦部掃掃瞄影像。 透過結構方程模型(Structural Equation Modeling, SEM)，我們嘗試結合腦部結構、功能性連結，與側化的句法處理策略三種不同類型的資料之間的關聯。我們發現在句法處理上左腦還是主要的優勢半腦，這會受到中後區左右半腦的靜息態功能性連結強弱所影響。而前區半腦間溝通則與右腦的句法處理反應以及右腦半腦內額葉顳葉間的連結性互相影響。總體而論，我們的發現對於側化的語言能力影響因素，提供了更全面的了解。

Syntactic processing has been known as one of the most left-lateralized of brain cognitive functions. However, the underlying mechanism of the functional lateralization seems uncertain. We combined three kind of measurements, event-related potentials (ERP), diffusion tensor imaging (DTI) and resting-state functional magnetic resonance imaging (RS-fMRI) to measure the correlations between structural connectivity (SC) of white matter tracts, resting-state functional connectivity (FC) within and between hemispheres, and online functional ERP responses during the processing of Chinese grammatical judgements at the phrase level in a split visual field paradigm. We investigated the relationships between intra- and inter-hemispheric connectivity and the lateralization of syntactic processing in younger adults. Twenty-four right-handed young adults without familial sinistrality were recruited in this experiment involving ERP, DTI and rs-fMRI data, with the MRI scan at resting state conducted within 7 months of the ERP experiment. By the spilt visual field presentation, we could collect the hemisphere-biasd ERP responses. Consistent to prior researches, we found the left-lateralized ERP response. We further analyzed the role of functional connectivity in the associations between language-processing-related white-matter structures and ERP indices of syntax processing by structural equation modeling (SEM). Our main finding is that there is a dominant role of LH in syntax processing which may associated with the functional connectivity between middle-posterior part of CC connected area. Functional connectivity between anterior part of CC connected area has bidirectional association with the functional response and frontal-temporal connection of RH. Overall, through analyzing these multimodal data jointly, we bridge some knowledge gaps in our understanding of the critical factors driving a left-lateralized language processing network.