顳葉癲癇者之錯誤記憶

Abstract

文獻指出錯誤記憶的產生與過度依賴要旨記憶及監控功能受損有關。Schacter、Verfaellie、及Pradere（1996）認為失憶症者與阿茲海默型失智症者之要旨記憶保留困難可能與內側顳葉結構損毀有關。然而，神經影像顯示，要旨記憶與內側顳葉有關，監控功能與額葉有關。因此，對於額葉亦受損的失憶症者與阿茲海默型失智症者來說，錯誤記憶表現可能無法排除監控能力受損的影響。基於上述，本研究欲透過腦部受損部位侷限於內側顳葉之顳葉癲癇病患，探討要旨記憶保留困難與內側顳葉結構受損的問題。並同時建立國內顳葉癲癇患者之神經認知功能的資料。 共有45位顳葉癲癇患者（左側16位、右側15位、及雙側14位），與22位正常人參與本研究。患者需符合：（1）EEG顯示顳葉異常放電；（2）MRI顯示內側顳葉硬化；（3）未曾接受過腦部手術；（4）未曾有影響認知功能的病史。正常人則需符合未曾有影響認知功能的病史。每位受試者需接受神經認知功能檢查與錯誤記憶作業。 研究結果發現：學習記憶方面，無論語文或視覺材料，左側及雙側患者均顯著低於正常人；語意記憶方面，左側、右側、及雙側患者均明顯低於正常人。錯誤記憶表現上，僅發現雙側患者顯著低於正常人。進一步資料分析顯示，雙側患者錯誤記憶少可能與旨記憶保留困難有關。 本研究結果顯示，雙內側顳葉結構在要旨記憶表現上扮演重要的角色，支持過去文獻（Schacter, Verfaellie et al., 1996）的看法。然而，本研究在判斷內側顳葉顳葉受損部位時，部分雙側患者僅依據MRI的發現，並非同時考慮EEG與MRI的結果，因此，本研究在結果的解釋上仍有其限制。關於顳葉以外區域異常放電是否影響錯誤記憶表現，需進一步研究。

Literature shows that false memory manifestation results from an overdependence on semantic gist and/or impaired ability to monitor information. Schacter and co-workers claimed that the retention deficit of semantic gist information in amnesic and demented patients with Alzheimer’s disease (AD) is presumably due to lesions of mesial temporal lobe structures. Accordingly, the underlying neural substrates involving gist memory have been suggested to be associated with mesial temporal regions, while source monitoring function has been proposed to be related to frontal lobe function. However, neuropathological involvement of frontal regions in these amnesic and AD patients might confound the results of these false memory studies. Using patients with temporal lobe epilepsy (TLE) due to unilateral or bilateral mesial temporal sclerosis bearing brain-damaged locations restricted to medial portions of temporal areas, the present study was thus to examine the issue of whether the impaired retention of semantic gist materials is associated with mesial temporal dysfunction. Meanwhile, this study made an attempt to document neurocognitive functions in our Taiwan patients with TLE. Forty-five patients with TLE (16 left, 15 right, and 14 bilateral) and 22 healthy controls participated in the study. The inclusion criteria for patients with TLE consisted of: (1) EEG abnormalities restricted to the temporal lobes; (2) no lesion other than mesial temporal lobe sclerosis on brain MRI; (3) no history of brain surgery; and (4) no physical and psychiatric illness. Normal control subjects were also free of neurological and psychiatric disorders. All subjects were given the false memory task and a battery of neurocognitive tests. The results revealed that left and bilateral TLE patients evidenced a significant deficit of delayed verbal and visual episodic and semantic memory function compared to their normal control counterparts, even after controlling for VIQ while only defective semantic memory manifested in right TLE patients. However, only bilateral TLE patients evidenced a low level of false memory functioning. Further data analysis revealed that a low level of false memory manifestation in bilateral TLE patient seemed to be related to a failure to retain gist information. Based on the present results, it appeared that bilateral mesial temporal structures might play an important role in gist memory functioning. These findings thus seemed further corroborate Schacter and colleagues’ claim. However, a caveat should be taken with care for interpreting the present results because only half of bilateral TLE patients did evidence lesions of mesial temporal lobes merely based on MRI rather than on both EEG and MRI findings. Thus, the issue of whether abnormal EEG sites other than temporal areas might affect false memory functioning remains unclear and awaits further investigation.