老化相關之靜息態功能連結半球不對稱性降低及語言情節記憶表現

Abstract

過去在靜息態功能性磁振造影的研究指出，預設模式網絡及警覺網絡，此二靜息態網絡特別容易受到老化作用的影響，且預設模式網絡的功能連結強度與老年人在語言情節記憶的表現有關。然而，此二靜息態網絡的功能連結是否存在左右大腦半球的差異，尚未被詳細探討。因此，本研究旨在探討靜息態功能連結在老化上的改變，特別著重在大腦半球的差異及其與語言情節記憶表現的關連性。本研究募集31 位健康年輕人，30 位健康老年人。所有受試者皆接受全套神經心理測驗評估，並使用種子相關分析方法研究靜息狀態的腦影像，最後透過相關分析方法研究靜息態功能連結與語言記憶表現的關聯性。結果顯示，老年人的左側大腦半球內及兩側大腦半球間的功能連結強度皆較年輕人弱，進而展現不對稱性下降的現象。此外，警覺網絡亦存在功能連結與特定記憶表現的關聯性，此關係並不僅存在於預設模式網絡中。本研究對於了解健康老化在靜息態功能連結的改變提供嶄新的發現，強調將大腦半球差異的因素納入未來研究之必要性，本研究亦顯示靜息狀態下大腦網絡的顯微改變與語言情節記憶表現的年齡差異密切相關，此發現為日後制定延緩及預防老化的認知訓練介入策略建構良好基礎。

Background and Objective: Previous resting-state fMRI studies have demonstrated that the default mode network (DMN) and salience network (SN) were both vulnerable to aging effects and the DMN associated with changes of verbal episodic memory in older adults. However, the relationship between the hemispheric differences in the functional connectivity (FC) of the brain networks and cognitive performance remains uncharacterized. Thus, the present study investigated age-related resting-state FC alteration, focusing on the hemisphere differences, and its association with verbal episodic memory performance. We hypothesized that the older adults would display hemispheric asymmetry reduction in RSFCs. In addition, FC strengths within and between the DMN and SN would be associated with performance on the verbal episodic memory. Methods: A sample of 61 community-dwelling healthy adults (young, n = 31, M = 22.71, SD = 2.44; old, n = 30, M = 66.97, SD = 4.20) participated in the study. All participants were administered a battery of standardized neuropsychological tests, including a verbal memory test, to assess domains of cognitive functioning as part of a larger study of cognitive aging. A seed-based analysis of the FC and statistical analysis were conducted to investigate the relationship between the FC and verbal memory performance. Results: The results revealed that the elderly demonstrated decreased both intra- and cross-hemisphere FCs compared to the young adults, therefore, resulting in hemispheric asymmetry reductions. Furthermore, not only FCs between regions within the DMN, but also FCs of brain regions in the SN were related to specific verbal episodic memory indices. Conclusion: Collectively, our findings provide valuable new information of resting-state FC in healthy aging, revealing an age-related reduced hemispheric asymmetry pattern of brain connectivity using resting fMRI, which was distinct from the task fMRI. A change in the organization of the neural networks underlying the episodic memory can also be responsible for the differences observed between young and older adults.