| 摘要: | 隨著人口高齡化，老化造成認知功能衰退的問題日趨嚴重，老化與認知功能的關係之研究也越來越被重視，其中工作記憶是高級認知功能的重要指標，也是認知老化基礎理論之一，過去的相關研究由於工作記憶的內部結構複雜以及研究者採用的實驗作業和實驗設置不一，使得研究結果分岐，總結來說，強調執行加工能力的工作記憶作業有較大的年齡效應，而以視覺空間為記憶材料的作業較以語言為材料的作業更容易受老化影響。然而工作記憶與老化的神經機制透過腦波技術的協助漸漸被了解，腦波是群體神經元同步振盪的結果，神經振盪的頻率以及power的改變與老化相關，其中alpha頻率範圍的腦波尤其被認為與執行工作記憶作業中，注意力集中在外部訊息以及保持記憶件的表現相關，過去研究顯示，刺激前的alpha power與隨後的表現相關，而編碼階段alpha power change (刺激前alpha power減去編碼階段的alpha power; alpha suppression)也與處理刺激的能力相關，但目前工作記憶力老化與alpha波之間的關聯尚未有系統化的文獻。
本研究為了瞭解老化與工作記憶的關係，募集39位年輕人(19-39歲)、30位中年人(40-64歲)和30位老年人(65歲以上)的健康受試者進行實驗，實驗中受試者將進行強調執行加工能力的工作記憶結合作業，隨後依據受試者進行工作記憶結合作業時的回答和腦波紀錄進行結果分析，分析方法根據信號偵測理論計算Pashler’s K value、d’和反應時間來做行為表現的指標，並且利用希爾伯特-黃轉換(Hilbert-Huang Transform, HHT)中遮罩的經驗模態分解法(Masking Empirical Mode Decomposition, Masking EMD)進行腦波分析，取第5個本質模態函數作為alpha波，計算枕葉電極的power平均值為腦波的指標。
分析結果顯示，中年人組與年輕人組的行為表現結果在Pashler’s K 和d’的數值無達顯著差異標準(p<0.05)，但在反應時間中，中年人組較年輕人組反應時間長達顯著標準，然而，老年人組的行為表現在三個指標中皆較年輕人組和中年人組表現差達顯著標準，此結果與其他用不同工作記憶力作業的老化相關研究有類似的趨勢。而在腦波的分析結果主要發現刺激前alpha power在老年人組較年輕人組低達顯著標準，中年人組與年輕人組在刺激前alpha power無顯著差異，進一步分析發現刺激前alpha power與Pashler’s K value和d’皆呈正相關達顯著標準，並與反應時間皆呈負相關達顯著標準，另外，在編碼階段alpha suppression的腦波指標中，年輕人組較中年人組和老年人組達顯著差異，而編碼階段alpha suppression與Pashler’s K value和d’皆呈顯著正相關。
總結而言，本研究重驗了過去工作記憶力隨老化下降的結果，並提出刺激前alpha power和編碼階段alpha suppression與工作記憶老化的關係，提供工作記憶表現與老化機制的客觀指標。;With aging, the issue and emphasis on cognitive decline among human population has become more serious. Research addressing the relationship between aging and cognitive function has also been receiving greater attention recently. Among all the cognitive functions, working memory is considered to be one of the most sensitive ones to aging. In prior studies, the complex internal structure of working memory and the experimental assignments and experimental settings used by the researchers are different, making the research results diverse and complex. In summary, working memory tasks that emphasize the ability to perform processing have a greater age effect. However, in order to better comprehend the brain mechanism of working memory decline, researchers used electroencephalography (EEG) in the study and proposed that neural oscillations and their synchronization play an important role in cognitive functions that require rapid formation of neural assemblies, such as visual working memory. Alpha power is believed to be related to the performance of focusing on external information and maintaining memory in the execution of working memory tasks. Past studies have shown that the alpha power before stimulation is related to the subsequent performance, and the alpha suppression in the encoding phase is also related to the ability to process stimuli, but there is currently no systematic literature on the relationship between aging of working memory and alpha power.
In order to understand the relationship between aging and working memory, the current study recruited 39 young adult (19-39 years old), 30 middle-aged (40-64 years old) and 30 elderly participants (over 65 years old). All participants had done working memory binding task that emphasize the ability to perform processing, with recoding EEG simultaneously. The analysis method calculation was used Pashler′s K value, d′ and reaction time according to the signal detection theory. EEG analysis used the masking empirical mode decomposition in the Hilbert-Huang Transform. We took the 5th intrinsic mode function as the alpha wave, and calculates the average power of the occipital lobe electrode as the EEG index.
It was observed that the behavioral performance results of the middle-aged group and the young group did not reach the standard of significant difference in Pashler′s K and d′, but the reaction time of the middle-aged group was significantly longer than that of the young group. However, the behavioral performance of the elderly group is significantly worse than that of the young and middle-aged groups in all three indicators. These results had a similar trend with other aging-related studies using different working memory tasks.
In the EEG results, It was observed that prestimulus alpha power is significantly lower in the elderly group than the young group and there is no significant difference between the middle-aged group and the young group. Further analysis, positive correlation between the prestimulus alpha power and Pashler′s K value / d′ was observed, while negative correlation between the prestimulus alpha power and reaction time was observed. In addition, the young group is significantly different from the middle-aged group and the elderly group on the value of alpha suppression in the encoding stage. Positive correlation between the alpha suppression in the encoding stage and Pashler′s K value / d′ was observed.
In summary, this study replicates the results of the decline in working memory with aging in the past, and proposes the relationship between alpha power before stimulation and alpha suppression in encoding stage and working memory aging, and provides objective indicators of working memory performance and aging mechanisms. |
