太極拳運動改善中老年人轉換任務功能之療效與神經機制探討：神經認知與神經影像研究

Abstract

背景：轉換任務能力是指能彈性地轉移注意力，以因應兩種或多重任務需求的能力。轉換任務能力是一種高階執行功能，會隨著年齡增加而下降。中年期是轉換任務能力下降的轉銜期，但具有個別化差異。過去罕有研究探討中年人如何調節大腦功能性活化，以預防或因應此轉換任務能力之下降。太極拳運動訓練已被證實能有效改善老年人之轉換任務表現。然而，太極拳運動訓練如何影響轉換任務相關神經機制仍是未知。本論文之目的有三：(1) 研究一為探討年輕人、中年人、及老年人之轉換任務能力及其相關腦部功能性活化之差異，尤其著重探討中年人之神經機制；(2) 研究二為探討太極拳運動訓練是否能有效改善老年人執行轉換任務時之腦部功能性活化；(3) 研究三為探討太極拳運動訓練是否能增加轉換任務相關之特定白質神經纖維束完整性，或特定白質神經纖維完整性之基準值是否會影響中老年人在太極拳運動訓練後增進轉換任務表現之效益。 方法：研究一採用修改版的史楚普(Stroop)功能性磁振造影測試，以評估年輕人(n = 30)、中年人(n = 30)、及老年人(n = 30)在執行非轉換任務及轉換任務測試時之腦部功能性活化及行為表現，並探討其腦部活化與行為表現間之關係。研究二使用相同的功能性磁振造影測試及隨機對照試驗設計，隨機分派老年人至太極拳組(n = 16)及控制組(n = 15)，並評估老年人在12週太極拳運動介入前、後之腦部功能性活化及轉換任務表現之變化。研究三使用擴散頻譜磁振造影及隨機對照試驗設計，隨機分派中老年人至太極拳組(n = 19)及控制組(n = 19)，探討中老年人在12週太極拳運動介入前、後，全腦白質神經纖維束及與轉換任務相關之特定白質神經纖維束的完整性之變化，也探討這些白質神經纖維束完整性之基準值與太極拳促進轉換任務效益之關係。白質神經纖維束完整性以普擴散不等向性分數(generalized fractional anisotropy)表示。在研究二及研究三中，太極拳組受試者接受為期12週、每週三次、每次60分鐘的楊式24式太極拳運動訓練介入，而控制組受試者則未接受任何訓練介入，僅維持其原生活形態，與接受每兩週一次的電話訪問。研究二及研究三除了蒐集影像資料之外，亦會蒐集轉換任務及身體功能之行為表現資料。 結果：研究一發現雖然三個年齡組之受試者皆有能力依據任務難度需求，調節兩側前額葉-頂葉腦區之功能性活化，但唯有中年人組呈現：在執行轉換任務測試時，左側前額葉活化愈高者，及從非轉換任務至轉換任務測試時，左側前額葉活化增加愈多者，其轉換任務錯誤愈少或反應時間愈短之現象(r = -0.374 – -0.569, p ≤ 0.05)。研究二及研究三皆發現太極拳運動訓練有促進轉換任務表現及身體功能之效益。研究二更發現，老年人在接受在12週太極拳運動訓練後，在執行轉換任務時，愈有能力提升前額葉活化者，尤其是左側上額迴(left superior frontal gyrus)之活化，其轉換任務錯誤減少得愈多(r = -0.631, p = 0.021)。研究三之結果發現，全腦白質神經纖維束(r = -0.747, p = 0.001)、與前額葉-紋狀體-視丘-前額葉迴路(prefronto-striatal-thalamo-prefrontal loop) (r = -0.800, p < 0.001)、及前額葉-頂葉/顳葉(prefronto-parietal/occipital) (r = -0.782, p < 0.001)之白質神經纖維束之基準值愈高者，12週太極拳運動訓練後之轉換任務錯誤減少得愈多。其中，前額葉-紋狀體-視丘-前額葉迴路白質神經纖維束完整性之基準值為預測12週太極拳訓練後之轉換任務進步量之最主要因子(β = -0.875, R2 = 0.495, p < 0.001)。 結論：整體而言，研究一之結果表示調節與轉換任務相關的左側前額葉活化的能力是中年人達成愈佳轉換任務表現之獨特神經機制。因此，建議提供有助於增加此調節能力之訓練，以預防隨年齡增加而來的轉換任務表現下降。研究二之結果建議，太極拳運動訓練是一種有助於提升轉換任務表現的運動型態，因太極拳運動訓練能提升一些老年人在因應轉換任務測試時，腦部前額葉活化之功能，雖然並非所有老年人皆能呈現此效益。研究三之結果突顯中老年人之前額葉-紋狀體-視丘-前額葉神經纖維束完整性基準值之重要性，較好的神經纖維束完整性有益於中老年人在12週太極拳運動訓練後，獲得較佳的轉換任務進步。

Background: The ability to flexibly shift attention and respond to two or multi-task demands is called task-switching ability. Task-switching ability is a high-level executive function and declines with age. The transition period of task-switching ability declines occurs at midlife, but with individual differences. Little is known about how middle-aged adults modulate brain activation to prevent or handle such declines. Tai Chi Chuan (TCC) exercise training has been shown to improve task-switching performance in older adults. However, how TCC exercise training induces changes in the neural mechanisms of task-switching remains unknown. This dissertation had three purposes: (1) to investigate age differences in non-switch and switch performances and associated functional activations across young, middle-aged, and older adults, with particular focus on the middle-aged in Study One; (2) to investigate whether TCC exercise training has effects on task-switching associated brain functional activations in older adults in Study Two; and (3) to investigate whether TCC exercise training enhances the integrity of specific task-switching associated white matter (WM) tracts and whether the baseline integrity of these tracts influences TCC training-induced task-switching improvement in middle-aged and older adults in Study Three. Methods: Study One used a modified Stroop task-functional magnetic resonance imaging (fMRI) paradigm to assess the brain functional activations and behaviors during non-switch and switch conditions, and their interrelationships in young (n = 30), middle-aged (n = 30), and older (n = 30) adults. Study Two used the same task-fMRI paradigm and a randomized controlled trial (RCT) design to examine the changes in functional activations and task-switching performances in older adults randomly assigned to a TCC group (n = 16) and a control group (n = 15) before and after a 12-week TCC exercise intervention. Study Three used diffusion spectrum imaging and a RCT design to investigate the changes in general fractional anisotropy (GFA) values, the indices of WM integrity, of the whole brain and specific task-switching associated WM tracts, and the relationships of the baseline GFA values of these WM tracts to task-switching improvement in middle-aged and older adults randomly assigned to a TCC group (n = 19) and a control group (n = 19) before and after the same 12-week TCC exercise training intervention used in Study Two. In both Studies Two and Three, the TCC group received training in the 24-form Yang-style of TCC exercise three times per week, 60 minutes each time, for 12 weeks. In contrast, the control group did not receive any intervention, but maintained the original lifestyles and received one telephone consultation biweekly. In addition to the imaging data, behavioral task-switching and physical functions were also measured. Results: Study One showed that although all three groups showed the ability to modulate the bilateral prefrontoparietal activations according to task demands, only the middle-aged adults showed that greater left prefrontal activations during task-switching or greater increases of these activations from non-switch to switch conditions were associated with less task-switching errors or shorter reaction time (r = -0.374 – -0.569, p ≤ 0.05). Both Study Two and Study Three showed TCC training-induced improvements in task-switching and physical function. Study Two further revealed that after 12 weeks of TCC training, the TCC participants who had the ability to recruit greater prefrontal activation, particularly in the left superior frontal gyrus, during task-switching presented greater reductions of task-switching errors (r = -0.631, p = 0.021). Study Three provided support for the importance of the baseline integrity of whole brain tracts (r = -0.747, p = 0.001) and specific task-switching associated WM tracts, the prefronto-striatal-thalamo-prefrontal loop (r = -0.800, p < 0.001) and the prefronto-parietal/occipital (r = -0.782, p < 0.001) fiber groups, in predicting error reductions of task-switching performance after 12 weeks of TCC training. In particular, the baseline integrity of the prefronto-striatal-thalamo-prefrontal loop fiber group was the predominant predictor of task-switching improvement after 12 weeks of TCC training (β = -0.875, R2 = 0.495, p < 0.001). Conclusions: Altogether, the results of Study One suggest that the ability to scale up task-switching relevant left prefrontal activation is a unique neural mechanism that middle-aged adults could employ to achieve better task-switching performance. Training that could enhance such modulation ability is therefore recommended to prevent age-related declines in task-switching. The findings of Study Two suggest that TCC could serve as one of type of exercise to enhance task-switching ability because this training could provide benefits to some, although not all, older adults to enhance the function of their prefrontal activations during task-switching. The results of Study Three highlight the importance of the baseline integrity of the prefronto-striatal-thalamo-prefrontal loop fiber group in helping middle-aged and older adults achieve more task-switching improvement after 12 weeks of TCC training.