輕度阿茲海默型失智患者之錯誤記憶

Abstract

正常的記憶運作仰賴適當的逐項記憶和要旨記憶，事件記憶缺損是阿茲海默型失智患者（AD患者）早期的臨床特徵，同時文獻指出該記憶缺損源自逐項記憶和要旨記憶的退化。然而AD患者語意記憶是否毀損目前仍有爭議，且要旨記憶缺損是源自語意系統毀損或語意訊息提取困難，目前尚不清楚。 DRM（Deese-Roediger-McDermot）派典是常被使用的錯誤記憶研究方法，可以用來反映要旨記憶的功能。過去研究發現，增加學習次數可提高AD患者使用要旨記憶，然而該結果無法獲得以黑白線條圖片或彩色照片為刺激作業研究結果的支持。以上不一致結果主要是研究方法的問題，本研究採用DRM派典呈現三種不同的刺激材料，比較AD患者及正常老人之錯誤記憶表現，重新探討上述問題 36位輕度AD患者與36位正常老人控制組參與本研究，在性別、年齡、及教育程度無顯著差異。每位受試者接受神經心理功能檢查和錯誤記憶作業，錯誤記憶作業分為語音搭配文字、黑白線條圖片、及彩色照片。結果發現，錯誤再認的表現上，文字和黑白線條圖片呈現時，AD患者顯著低於正常老人，但彩色照片呈現時，和正常老人無顯著差異。正確再認的表現上，不管學習的情境為何，AD患者均顯著低於正常老人。AD患者正確和錯誤再認均受學習材料的影響，彩色照片作業的分數表現高於黑白線條圖片，黑白線條圖片則又高於文字，但三者分數表現並無明顯差異。正常老人僅在正確再認有類似的結果。 本研究結果顯示輕度AD患者語意記憶確實有缺損的問題，但聽覺學習搭配彩色照片似乎可提高AD患者要旨記憶的功能。有鑑於此，筆者較支持輕度AD患者要旨記憶缺損來自語意知識提取的困難，而非語意記憶毀損的論點。然而本研究的樣本較小，未來尚需較大樣本來做進一步的探討。

Normal memory depends upon both adequate verbatim and gist memory functioning. The deficit of episodic memory is one of the early clinical features in patients with Alzheimer’s disease (AD), and literature shows dysfunction of verbatism and gist memory processing in these patients contributing to such memory impairment. However, the issue regarding whether impairment of semantic memory, that is mainly reflected by gist memory functioning, exists in the early stage of AD patients remains unclear. Furthermore, the related issue of whether deficit of gist memory evident in those AD patients is primarily due to a loss of semantic structure or an inability to get access to semantic knowledge is also in question. The Deese-Roediger-McDermot (DRM) paradigm has been one of the important procedures to approach gist memory functioning in the light of manifestation of false memory. Having used this paradigm, researches revealed that an increase of stimulus exposure trials could facilitate AD patients’ gist memory functioning. However, such findings could not be fully confirmed by other investigations with a manipulation of stimulus features, such as using black-and-white line drawings or colored photos as stimulus items. Methodological pitfalls in these studies might account for these inconsistent outcomes. Using the DRM paradigm in which three forms of stimuli were exposed to normal healthy elderly controls and AD patients, the present study was thus to re-explore these controversial issues. Thirty-six mild AD patients and thirty-six normal healthy elderly controls matched for the sex, age, and education level participated in the study. All subjects were given a battery of neuropsychological tests and the false memory tasks in which subjects received three types of stimulus conditions, including auditory words with visual words, with black-and-white line drawings, and with colored photos. The results revealed that AD patients’ false memory index scores on the false memory tasks, involving stimulus conditions of auditory words plus either visual words or black-and-white line drawings were significantly lower than those of their normal counterparts. In contrast, these index scores on the task with the stimulus feature of auditory words plus colored photos were not significantly different between these two subject groups. For the true index score of the task, the patients were remarkably lower than their normal counterparts, irrespective of the stimulus conditions. These patients’ true and false memory index scores varied with stimulus conditions, that is both true and false memory index scores of the stimulus condition involving color photos were the best followed by the condition involving black-and-white line drawings, and words. Nevertheless, the index score differences among these three conditions were not statistically significant. For normal healthy elderly controls, the similar index score pattern was only evident in their true recognition performance. Based on these results, it appeared that mild AD patients did have semantic memory problem. However, auditory memory task items accompanying with their corresponding colored photos, could facilitate mild AD patients’ gist memory functioning. Accordingly, it is thus suggested that at least mild AD patients’ gist memory problem would be mostly like to be associated with an inability to get access to semantic knowledge rather than a loss of semantic structure. Nonetheless, since the current results were merely based on a small sample, further study on a large scale to investigate these issues is necessary.