視覺空間位置工作記憶的老化效應： 功能性磁振造影研究

Abstract

為了探討老化對視覺空間位置工作記憶背後的神經機制，本研究使用事件關聯式設計(event-related design)的功能性磁振造影，分別量測登錄期(encoding phase)、維持期(maintenance phase)和提取期(retrieval phase)的BOLD訊號，並利用此訊號計算多尺度熵 (Multi-scale Entropy)。15位年輕人以及15位老年人參與研究，任務難度分為2、3和4個記憶數量，受試者須同時記住物體和空間資訊。神經影像實驗結果顯示，老年人與年輕人的大腦活動型態與PASA、HAROLD和ELSA模型一致，BOLD訊號複雜度則符合CRUNCH假說。在年輕人組，左腦海馬體(hippocampus)和左腦海馬旁回(parahippocampal gyrus)的活化和答題的正確度呈現負相關(r=-.466, p=0.040)。合併年輕人和老年人組，左腦梭狀迴(fusiform gyrus)和右腦島葉(insula)的活化與反應時間呈現負相關(r=-.34, p=0.033; r=-.31; p=0.0477)。此外，實驗結果亦觀察到小腦、海馬體、前扣帶迴(anterior cingulate)和基底核(basal ganglia)可能在視覺空間位置工作記憶中扮演重要角色，尤其是海馬體，其在年輕人組呈現較高的活化，但老年人組卻呈現較高的複雜度。使用多尺度熵計算fMRI訊號的複雜度可成為探討老化的方法之一，它可提供訊號變動的程度，作為老年人試圖利用補償方式維持任務表現的證據之一。

In this study, we investigated the neural correlates of age-related differences in visual-spatial working memory with BOLD signal and signal entropy utilizing event-related design fMRI. 15 healthy young adults and 15 healthy older adults performed visual-spatial working memory (VSWM) tasks with set sizes from 2 to 4. The results shows consistent neuroimaging results with PASA, HAROLD and ELSA models and consistent entropy results with CRUNCH theory in VSWM with age. Furthermore, the results demonstrated that greater activity in the left hippocampus and left parahippocampal gyrus negatively correlated with accuracy in younger adults(r=-.466, p=0.040). In both age groups, greater activity in the left fusiform gyrus and right insula negatively correlated with response time (r=-.34, p=0.033; r=-.31; p=0.0477). We observe cerebellum, hippocampus, anterior cingulate and basal ganglia may play important roles in VSWM, especially hippocampus which display greater activation in younger adults but higher entropy in older adults. We conclude that the measure of fMRI signal entropy is a complementary and potential method to investigate the aging effects