Neurobiology Research Unit, Copenhagen University Hospital Rigshospitalet, Copenhagen, Denmark.
Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
J Sleep Res. 2024 Dec;33(6):e14226. doi: 10.1111/jsr.14226. Epub 2024 Apr 27.
The glymphatic system is centred around brain cerebrospinal fluid flow and is enhanced during sleep, and the synaptic homeostasis hypothesis proposes that sleep acts on brain microstructure by selective synaptic downscaling. While so far primarily studied in animals, we here examine in humans if brain diffusivity and microstructure is related to time of day, sleep quality and cognitive performance. We use diffusion weighted images from 916 young healthy individuals, aged between 22 and 37 years, collected as part of the Human Connectome Project to assess diffusion tensor image analysis along the perivascular space index, white matter fractional anisotropy, intra-neurite volume fraction and extra-neurite mean diffusivity. Next, we examine if these measures are associated with circadian time of acquisition, the Pittsburgh Sleep Quality Index (high scores correspond to low sleep quality) and age-adjusted cognitive function total composite score. Consistent with expectations, we find that diffusion tensor image analysis along the perivascular space index and orbitofrontal grey matter extra-neurite mean diffusivity are negatively and white matter fractional anisotropy positively correlated with circadian time. Further, we find that grey matter intra-neurite volume fraction correlates positively with Pittsburgh Sleep Quality Index, and that this correlation is driven by sleep duration. Finally, we find positive correlations between grey matter intra-neurite volume fraction and cognitive function total composite score, as well as negative interaction effects between cognitive function total composite score and Pittsburgh Sleep Quality Index on grey matter intra-neurite volume fraction. Our findings propose that perivascular flow is under circadian control and that sleep downregulates the intra-neurite volume in healthy adults with positive impact on cognitive function.
脑淋巴系统以脑脑脊液流动为中心，在睡眠期间增强，而突触稳态假说则提出睡眠通过选择性突触缩小来作用于大脑微观结构。虽然迄今为止主要在动物中进行研究，但我们在这里检查人类的大脑扩散率和微观结构是否与一天中的时间、睡眠质量和认知表现有关。我们使用来自 916 名年龄在 22 至 37 岁之间的年轻健康个体的弥散加权图像，这些图像是人类连接组计划的一部分，用于评估血管周围空间指数、白质各向异性分数、神经元内体分容积分数和神经元外体平均扩散率的弥散张量图像分析。接下来，我们检查这些测量值是否与采集的昼夜时间、匹兹堡睡眠质量指数（高分对应低睡眠质量）和年龄调整后的认知功能总综合评分相关。与预期一致，我们发现血管周围空间指数的弥散张量图像分析和眶额灰质神经元外体平均扩散率与昼夜时间呈负相关，而白质各向异性分数与昼夜时间呈正相关。此外，我们发现灰质神经元内体分容积分数与匹兹堡睡眠质量指数呈正相关，而这种相关性是由睡眠时间驱动的。最后，我们发现灰质神经元内体分容积分数与认知功能总综合评分呈正相关，以及认知功能总综合评分与匹兹堡睡眠质量指数之间的负交互作用对灰质神经元内体分容积分数的影响。我们的研究结果表明，血管周围的流动受到昼夜节律的控制，而睡眠下调了健康成年人的神经元内体分容积，对认知功能产生了积极的影响。
