National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD, USA; Behavioral Biology Branch, Center for Military Psychiatry and Neuroscience Research, Walter Reed Army Institute of Research, Silver Spring, MD, USA.
National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD, USA.
Neuroimage. 2019 Jan 15;185:263-273. doi: 10.1016/j.neuroimage.2018.10.043. Epub 2018 Oct 17.
The role of sleep in brain physiology is poorly understood. Recently rodent studies have shown that the glymphatic system clears waste products from brain more efficiently during sleep compared to wakefulness due to the expansion of the interstitial fluid space facilitating entry of cerebrospinal fluid (CSF) into the brain. Here, we studied water diffusivity in the brain during sleep and awake conditions, hypothesizing that an increase in water diffusivity during sleep would occur concomitantly with an expansion of CSF volume - an effect that we predicted based on preclinical findings would be most prominent in cerebellum. We used MRI to measure slow and fast components of the apparent diffusion coefficient (ADC) of water in the brain in 50 healthy participants, in 30 of whom we compared awake versus sleep conditions and in 20 of whom we compared rested-wakefulness versus wakefulness following one night of sleep-deprivation. Sleep compared to wakefulness was associated with increases in slow-ADC in cerebellum and left temporal pole and with decreases in fast-ADC in thalamus, insula, parahippocampus and striatal regions, and the density of sleep arousals was inversely associated with ADC changes. The CSF volume was also increased during sleep and was associated with sleep-induced changes in ADCs in cerebellum. There were no differences in ADCs with wakefulness following sleep deprivation compared to rested-wakefulness. Although we hypothesized increases in ADC with sleep, our findings uncovered both increases in slow ADC (mostly in cerebellum) as well as decreases in fast ADC, which could reflect the distinct biological significance of fast- and slow-ADC values in relation to sleep. While preliminary, our findings suggest a more complex sleep-related glymphatic function in the human brain compared to rodents. On the other hand, our findings of sleep-induced changes in CSF volume provide preliminary evidence that is consistent with a glymphatic transport process in the human brain.
睡眠在大脑生理学中的作用尚未被充分理解。最近的啮齿动物研究表明，与清醒状态相比，睡眠期间脑内的糖质分解产物清除系统（glymphatic system）能够更有效地清除废物，这是由于细胞外间隙的扩张促进了脑脊液（CSF）进入大脑。在这里，我们研究了睡眠和清醒状态下大脑中的水扩散系数，假设睡眠期间水扩散系数的增加将与 CSF 体积的扩张同时发生 - 这种效应我们基于临床前发现进行了预测，认为在小脑最为显著。我们使用 MRI 测量了 50 名健康参与者的大脑中表观扩散系数（ADC）的慢和快成分，其中 30 名参与者比较了清醒与睡眠状态，20 名参与者比较了一夜睡眠剥夺后的休息-清醒与清醒状态。与清醒相比，睡眠与小脑和左侧颞极的慢 ADC 增加以及丘脑、岛叶、海马旁回和纹状体区域的快 ADC 减少有关，睡眠觉醒的密度与 ADC 变化呈负相关。睡眠期间 CSF 体积也增加，并且与小脑的 ADC 变化有关。与休息-清醒相比，睡眠剥夺后清醒时的 ADC 没有差异。尽管我们假设睡眠时 ADC 增加，但我们的发现揭示了慢 ADC 的增加（主要在小脑）和快 ADC 的减少，这可能反映了快和慢 ADC 值与睡眠的不同生物学意义。虽然初步，但我们的发现表明，与啮齿动物相比，人类大脑中与睡眠相关的糖质分解产物清除系统具有更复杂的功能。另一方面，我们发现睡眠诱导的 CSF 体积变化提供了初步证据，与人类大脑中的糖质分解产物清除系统运输过程一致。
