執行轉換任務時與干擾處理相關之大腦額葉紋狀體活化與年齡差異

Frontostriatal Activation Correlates of Interference Resolution in Task Switching and Age Differences

陳乃綺(Nai-Chi Chen)

指導教授 ： 湯佩芳

國立臺灣大學/醫學院/腦與心智科學研究所/碩士(2017年)

https://doi.org/10.6342/NTU201704264

摘要

研究背景：過去研究顯示，老年人在執行認知任務時，若刺激物之雙價特徵相互衝突，其干擾處理表現會比年輕人來得差，而此年齡差異在任務規則呈現動態轉換時又會更加明顯。然而，中年人雖處於認知老化的重要過渡期，其干擾處理能力仍鮮少被人探討。本研究旨在探討認知功能正常之年輕人、中年人和老年人身的行為表現以及相關神經機制，並且著重探討前額葉激—紋狀體神經活化。

研究方法：本研究使用混合事件相關區塊實驗設計，受試者在掃描期間會在非任務轉換與任務轉換兩種情境下執行數字史楚普作業，納入分析之受試者共有35位年輕人 (平均年齡25.7歲；介於20.2至33.8歲)，38位中年人 (平均年齡59.1歲；介於52.0至63.5歲) 和36位老年人 (平均年齡70.4歲；介於65.4至80.1歲)。在每次試驗題中，受試者會接受具有雙價特徵（字型大小與數值多寡）的成對數字視覺刺激，其必須根據成對數字本身的顏色線索提取相對應的任務規則，判斷數字大小並作出適當按鍵反應。在一致性刺激之試驗題中，不論是依據相關或不相關的規則，其正確反應會是相同，干擾效應不會產生；在不一致刺激之試驗題中，根據兩個規則會各自對應至不同的正確反應，因此會產生干擾效應。在非轉換情境時，單一實驗區塊中僅會一種任務規則重複試驗；在轉換情境下，兩種任務規則會在單一實驗區塊以偽隨機模式交替呈現。我們記錄並分析受試者在執行該作業時，與干擾處理相關的行為資料(正確率及反應時間)和腦活化型態。

研究成果與討論：在行為結果中，我們發現反映在正確率上的干擾效應在轉換情境時會大於非轉換情境，然而上述現象在各年齡組間並未呈現差異。在神經影像結果中，我們發現任務轉換情境下的干擾處理之紋狀體神經活化位置，會隨著老化過程由尾核逐漸轉移至殼核。此外，在任務轉換情境下，年輕人組和中年人組可藉由提升雙側額下回腦活化來執行干擾處理，然而該區域之活化在老年人組並未達到顯著提升。行為與腦活化之相關性分析結果顯示，在年輕人組中，雙側尾核活化程度越大，其行為正確率受干擾刺激之影響較小，顯示年輕人可成功使用由上而下的過濾機制進行早期干擾處理；在老年人組中，背側前扣帶迴活化程度越大，其行為正確率受干擾刺激之影響較小，顯示老年人可能較依靠警覺網路並且傾向在反應選擇階段進行干擾處理。

結論：執行轉換任務時，年輕人與中年人的前額葉—背側紋狀體神經網路之有效活化可於抑制不相關刺激時發揮重要作用，相對而言老年人較依靠警覺網路和感覺運動紋狀體來完成此任務需求。

關鍵字

老化 ； 抑制控制 ； 執行功能 ； 紋狀體 ； 數字史楚普作業 ； 功能性磁振造影

並列摘要

Background: Research showed that older adults have more difficulty than young adults with resolving interference from conflicting bivalent stimuli. This age difference could be more prominent when the relevance of stimulus features changes dynamically during task-switching. However, it remains unknown whether the middle-aged, who are in the important transitional stage of cognitive aging, would behave more similarly to the young or the older in their interference resolution ability during task-switching. Therefore, this study was aimed to investigate this effect behaviorally as well as the associated neural mechanisms, especially those pertaining to the frontostriatal activations, across cognitively normal young, middle-aged, and older adults.
Methods: We used a hybrid event-related block design of functional magnetic resonance imaging (fMRI) experiment. Participants had to perform a modified numerical Stroop task in the non-switch and switch conditions. Cognitive intact young (n=35, age= 25.7 ± 4.2 years, 20.2 - 33.8 years), middle-aged (n=38, 59.1 ± 3.4 years, 52.0-63.5 years) and older adults (n=36, 70.4 ± 4.0 years, 65.4 - 80.1 years) were enrolled in this study. In each trial, participants were presented with digit pair stimuli of bivalent attributes (i.e., physical size and numerical value) and were instructed to compare two digits and make button response according to the relevant task-rule (the physical size discrimination or numerical value discrimination rule), which was cued by color of the digit stimuli. In the congruent trials, the correct responses would be the same according to either relevant or irrelevant rule, creating no interference effects. In the incongruent trials, the correct responses would be different according to the two rules, creating the interference effects. In the non-switch condition, the physical size and numerical size rule was tested in repeated trials of two separate blocks; in the switch condition, the rules changed pseudorandomly between trials in one block. The behavioral interference effects on accuracy and reaction time (RT) and brain activations related to interference effect were recorded and analyzed.
Results & Discussion: Behaviorally, we found that the interference effect on accuracy was greater in the switch than in the non-switch condition, but there was no age difference in this interference effect between switch and non-switch conditions. Neuroimaging results revealed that during task-switching, the striatal activations for interference resolution gradually shifted from primarily the caudate in the young, to the caudate plus the putamen in the middle-aged, and to primarily the putamen in the older. In addition, while the bilateral inferior frontal gyri were significantly activated for interference resolution in the switch condition in the young and middle-aged, these two regions were not significantly activated in the same condition in the older adults. Correlation analyses between behavioral measures and brain activations showed that in the young adults, greater bilateral dorsal caudate activations were related to a smaller interference cost in behavioral accuracy, suggesting their successful use of top-down filtering mechanisms for early interference resolution; while in older adults, greater activation in the dorsal anterior cingulate was correlated with a smaller interference cost in accuracy, which may suggest their shift to rely on the salient network and interference resolving during response selection stage.
Conclusions: Effective recruitment of the prefronto-dorsostriatal network might play an important role in successful suppression of irrelevant stimuli during task-switching in young and middle-aged adults. In contrast, older adults may rely on the salient network and sensorimotor striatum to achieve this task.

並列關鍵字

aging ； inhibition control ； executive function ； striatum ； numerical Stroop task ； fMRI

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