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Frontostriatal Activation Correlates of Interference Resolution in Task Switching and Age Differences
aging,inhibition control,executive function,striatum,numerical Stroop task,fMRI,
|Publication Year :||2017|
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。
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.
|Appears in Collections:||腦與心智科學研究所|
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