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    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/66116


    Title: 以非侵入式腦刺激探討左後側頂葉與情節記憶提取之因果關係;Using noninvasive brain stimulation to examine the causal relationship between the left posterior parietal cortex and episodic memory retrieval
    Authors: 駱建銘;Lo,Chien-Ming
    Contributors: 認知與神經科學研究所
    Keywords: 情節記憶;記憶提取;經顱電刺激;高脈沖式經顱磁刺激;episodic memory;retrieval;tDCS;cTBS
    Date: 2014-10-23
    Issue Date: 2014-11-24 15:46:15 (UTC+8)
    Publisher: 國立中央大學
    Abstract: 眾多功能性神經造影研究一致地發現,左後側頂葉(left posterior parietal cortex)在成功提取情節記憶(episodic memory)時會有活化的現象。然而,由於造影研究僅能針對觀察到的腦部活動及認知功能提供相關性的證據,左後側頂葉對於成功提取情節記憶時的活動並不代表左後側頂葉與記憶提取之間有因果關係。傳統上探腦部活動與認知功能是否具因果關聯性的方法是觀察特定腦區受損的病人是否也呈現相對應的認知缺損。早期神經心理學的研究甚少報告頂葉受損的病人出現情節記憶的缺損,而近期使用較敏感記憶測試方法的神經心理學實驗則發現頂葉受損的病人可能有輕微的記憶缺失。這些神經心理學的發現很明顯的並不支持情節記憶的提取需要左後側頂葉的參與。這種不一致的發現可能導因於神經心理學研究中腦傷病人受傷位置的變異,腦部其他區域功能補償,以及病人使用不同策略,以致沒有觀察到對應的認知功能減損。這些可能的問題可藉由使用非侵入式腦刺激研究方法避免,藉由暫時性的干擾某些特定腦區,觀察相對應的知功能表現是否發生不同。迄今為止有少數關於頂葉與情節記憶提取的非侵入式腦刺激方法研究,但這些研究因實驗設計的問題或是使用的記憶測試對於情節記憶不具足夠的敏感性,因此彼此之間的結果並不一致,對於左後頂葉與情節記憶提取之間的因果關係仍無定論。
    由於能夠提取帶有情境訊息的清晰記憶(recollection)是情節記憶很重要的一個特點,本研究利用可以量化清晰記憶的來源記憶測驗(source memory task)作為成功提取情節記憶的指標,並使用經顱直流電刺激(transcranial direct current stimulation)與經顱磁刺激(transcranial magnetic stimulation)兩種非侵入式腦部刺激儀器探討左後頂葉的活動與情節記憶提取之間是否具有因果關係。實驗一探討在記憶提取的過程中以經顱電刺激影響左後側頂葉是否會對記憶表現有所影響。受試者被隨機分派至陽極組與陰極組並分別只會接受陽極或是陰極的電刺激,且在三天的實驗中分別進行三次來源記憶測驗。在這三次測驗中,受試者於記憶提取的過程中同時接受在左後側頂葉位置的電刺激、假性刺激(sham)、或主要動作皮質區(M1)的電刺激。實驗結果顯示,雖然陽極組上並沒有看到記憶表現因為電刺激有所改變,但來源記憶的正確率受到陰極在左後側頂葉位置的電刺激後顯著的降低,而再認記憶的表現不受影響,顯示出以陰極直流電減低左後側頂葉的神經活動干擾情節記憶的表現。實驗一的結果提供了支持左後側頂葉與情節記憶提取存在著因果關係的證據。由於神經造影的研究顯示左後側頂葉內的角迴(left angular gyrus)的活化似乎與提取出清晰記憶有很大的關聯,但是經顱直流電刺激的空間解析度較差,無法單獨刺激角迴這個區域而不影響其他可能與記憶提取相關的區域,實驗二因此使用能精確影響特定腦區的經顱磁刺激來探究左後側頂葉中的角迴是否在提取清晰記憶中扮演著重要的角色。實驗二利用抑制性的連續性高脈衝式經顱磁刺激(continuous theta burst stimulation)來影響角迴這個腦區。受試者會進行三次來源再認記憶測驗,並且會在三次提取階段前分別接受在角迴位置的刺激、假性刺激、或是頂點(vertex)刺激。實驗結果顯示,受試者不論是再認記憶表現或者是來源記憶表現都沒有受到於角迴的經顱磁刺激的影響。為了確認實驗二的結果並不是因為連續性高脈衝式經顱磁刺激的強度不足所致,實驗三召回實驗二的受試者,並使用先前的刺激參數與腦區坐標讓受試者接受角迴位置的刺激或假性刺激。受試者接受刺激後進行數字大小比較作業(magnitude comparison task)以及特徵聯結搜尋作業(conjunction search task)。選擇這兩個作業是因為在先前的研究發現對角迴進行干擾可以影響這兩個作業的表現。實驗三的結果顯示,相較於假性刺激,對角迴的刺激可以干擾以上兩個作業的表現,代表著實驗二所使用的刺激參數至少可以影響某些牽涉角迴的認知作業。
    總結來說,實驗一提供了左後側頂葉與情節記憶提取有因果關係的支持證據,但是實驗二的結果並沒有證據顯示只影響角迴這個腦區可以對記憶提取的表現有所影響,而這個結果由實驗三看來可能不是低強度的刺激所導致。雖然在腦造影研究中角迴不斷的出現與提取清晰記憶相關的活化,但從實驗結果看來,角迴在情節記憶提取裡可能只扮演著非常輕微的角色。未來研究可能需要考慮個別定位提取清晰記憶時有高度活化的角迴坐標,以及文字與圖片刺激材料是否會活化不同的角迴區域來釐清角迴對於情節記憶提取的因果關係。

    ;Activations in the left posterior parietal cortex (LPPC) have been consistently reported in functional neuroimaging studies of episodic memory retrieval. However, it remains unclear whether this area is causally related to episodic memory retrieval. The correlational nature of neuroimaging studies makes it difficult to assert a causal relation between the LPPC activity and episodic retrieval. Furthermore, patient studies give rise to inconsistent results with regards to whether parietal lesions result in memory deficits. There have been a few noninvasive brain stimulation studies addressing this issue but the results were not consistent, possibly due to the fact that their designs were not optimal.
    A defining characteristic of episodic memory is recollection. Two experiments reported in this thesis hence employed a source memory task to index recollection and applied the noninvasive stimulation methods of transcranial direct-current stimulation (tDCS) and transcranial magnetic stimulation (TMS) to examine whether LPPC activity is causally related to episodic memory retrieval. In Experiment 1, twenty-four participants were randomly assigned to the anodal or the cathodal group and performed source memory tests on three separate days. During the retrieval phase, the participants received anodal or cathodal stimulation over the LPPC, sham on the LPPC, and stimulation on primary motor cortex (M1) as a control condition. The results indicated that source memory accuracy, but not old/new recognition performance, decreased significantly in the cathodal group when subjects received stimulation on the LPPC region compared with sham and M1 conditions. No such effect was found in the anodal group. The results of Experiment 1 supported the claim that the LPPC is causally related to episodic retrieval. In neuroimaging studies, the activation of the left angular gyrus (lAnG) within the LPPC was found to be associated with recollection process during retrieval, but the spatial resolution of tDCS was not able to stimulate such specific brain region without affecting adjacent regions. Hence, TMS, a more focal brain stimulation technique, was used in the second experiment. In Experiment 2, to further investigate the causal involvement of the lAnG in the recollection process, continuous theta burst stimulation (cTBS), which is an inhibitory repetitive TMS stimulation method, was employed. Twelve subjects performed a source memory task in which they had to make two source judgments. The cTBS was administered over the lAnG or vertex before the retrieval stage. The results showed no differences in the performances of both old/new recognition and source accuracy across the lAnG stimulation, sham, and vertex control conditions. In Experiment 3, to test whether the null results of Experiment 2 were due to insufficient cTBS intensity, eleven participants of Experiment 2 were recruited in Experiment 3. They received the cTBS with the same protocol used in Experiment 2 and then engaged in a magnitude comparison task and a visual conjunction search task. The results showed that performance in both tasks were lower after the cTBS over the lAnG relative to the sham condition, suggesting that the cTBS protocol used in Experiment 2 can influence at least some cognitive functions.
    Taken together, the tDCS study provided supportive evidence that the LPPC is causally related to episodic retrieval, whereas the cTBS study failed to reveal the causal relationship between the lAnG and recollection process. The null results of the cTBS study most likely was not due to insufficient cTBS intensity, as Experiment 3 showed that conjunction search and magnitude comparison were modulated by cTBS of the same protocol. These results may imply that the role of the lAnG in episodic retrieval is subtle or secondary. Another possible implication is that the appropriate lAnG location that are highly correlated with recollection should be identified individually so that a more consistent result can be revealed. Future studies also need to consider if textual and pictorial stimuli activate different regions within the angular gyrus in order to further clarify the causal relationship between the lAnG and episodic retrieval.
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