中文摘要：
從睡眠中醒來到完全清醒，睡眠遲惰現象是一個不斷變化的動態過程，伴隨著主觀困倦感與客觀認知表現下降。為了衡量睡眠遲惰期間的認知表現，研究者通常選用與警覺作業相關的行為範式。關於其神經生理機制，近期雖有研究表明該現象與早期清醒狀態的大腦自發性動態重組有關， 但未曾與認知功能下降建立直接聯繫。因此本實驗採用腦電波融合功能性磁振造影(EEG-fMRI)的測量，並通過對16位受試睡前醒後多次的心理動作警覺任務（PVT）與靜息態影像的掃描（共四次：睡前一次，醒後三次），旨在進一步揭示睡眠遲惰現象的潛在神經基礎並幫助我們理解醒後大腦功能重組對於認知行為表現之意義。我們的行為結果表明，相較於初始的清醒狀態，醒後50分鐘後受試的反應速度之標準差有顯著增加。進一步的交互效應分析顯示，相較於平均反應速度，在50分鐘後最快20%的PVT反應速度有顯著變快趨勢。在腦活動的變化上，時間維度的主效應存在於右側額下回，頂葉下回以及雙側的丘腦。值得關注的是，在任務和靜息兩種模態下前扣帶迴網路下的丘腦區域都受到睡眠遲惰效應的影響。在早期清醒時段，丘腦在任務下的微弱激活強度顯著與受試的反應速度正相關。並且，丘腦區域激活強度在醒後的逐漸回復伴隨著靜息狀態下腦連結和低頻振蕩指標的同時上升，儘管這些靜息態指標不能直接反映PVT下的激活強度。綜上所述，我們的研究表明在睡眠遲惰期間，前扣帶迴網路下丘腦區域的激活不足，但是卻能顯著地決定著當下的行為表現，而其他相關區域似乎也受到睡眠遲惰的影響而無法正常工作。這一現象可能代表著睡眠遲惰效應所導致的任務狀態下短期認知功能受損的潛在神經生理機制。

Abstract:
Sleep inertia (SI) depicts a transition phase from initial awakening to well-functioned wakefulness, as noted for its objective performance decline with the persistence of subjective drowsiness. The cognitive impairments in the SI period were conventionally measured by alertness-related behavioral tasks. To reveal its neural mechanisms, recent studies demonstrated the altered spontaneous reorganizations of neural networks along early wakefulness. However, the linkage between the resting-state network organizations and the cognitive impairments remains missing. In this study, using four-time EEG-fMRI acquisitions of both Psychomotor vigilance task (PVT) and resting sessions (before sleep and three times after awakening) on sixteen subjects at midnight, we aim to uncover the neural substrates of sleep inertia via alertness tasks and meanwhile to interpret the role of resting reorganization in PVT performances. Our results indicated that in the initial wakefulness after a nocturnal nap, the standard deviation of response speed decreased as compared to the latest wakefulness at around 50 mins after awakening. The performance impairment of fastest trials (top 20%) was observed on initial wakefulness, evidenced by a significant interaction with mean speed performance. In brain activity, the right-side inferior frontal gyrus, superior parietal cortex and the bilateral thalamus showed the time effect in repeated-measure Friedman test. Importantly, within Cingulo-Opercular Network (CON), thalamus showed the most prominent SI effect after awakening, observed from both resting and task modalities. During early post-sleep wakefulness, the insufficient thalamus activations in PVT contributed to mean response speed during the SI period. The rebound of the thalamus activation was parallel to its fluctuation in multiple resting indices, such as functional connectivity to CON and the ALFF, whereas the resting-state indices did not show correlation with PVT activation. Under vigilance task demand, our findings suggest that the weak activation of CO network, especially in thalamus, was in charge of the alertness maintenance in the SI period while other alertness-related nodes were unable to function normally during this period, which could be served as the neural signatures underlying the alertness impairments during sleep inertia.

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