Large-Scale Cortical Dynamics of Sleep Slow Waves

Slow waves constitute the main signature of sleep in the electroencephalogram (EEG). They reflect alternating periods of neuronal hyperpolarization and depolarization in cortical networks. While recent findings have demonstrated their functional role in shaping and strengthening neuronal networks, a large-scale characterization of these two processes remains elusive in the human brain. In this study, by using simultaneous scalp EEG and intracranial recordings in 10 epileptic subjects, we examined the dynamics of hyperpolarization and depolarization waves over a large extent of the human cortex. We report that both hyperpolarization and depolarization processes can occur with two different characteristic time durations which are consistent across all subjects. For both hyperpolarization and depolarization waves, their average speed over the cortex was estimated to be approximately 1 m/s. Finally, we characterized their propagation pathways by studying the preferential trajectories between most involved intracranial contacts. For both waves, although single events could begin in almost all investigated sites across the entire cortex, we found that the majority of the preferential starting locations were located in frontal regions of the brain while they had a tendency to end in posterior and temporal regions.

脑电图（electroencephalogram, EEG）信号中，慢波是睡眠阶段的核心特征标识，其反映了皮层神经网络内神经元超极化与去极化的交替周期。尽管已有研究证实慢波在塑造与强化神经元网络方面具备功能作用，但目前学界仍难以在人类大脑中对这两个过程开展大规模的特征刻画。本研究采用10名癫痫患者的同步头皮脑电图与颅内脑电记录，对人类大范围皮层区域内超极化波与去极化波的动态变化进行了分析。研究发现，超极化与去极化过程均可呈现两种不同的特征时长，且该特征在所有受试者中均保持一致。针对这两类波，本研究测算得到其在皮层上的平均传播速度约为1 m/s。最后，本研究通过分析颅内电极触点间的优先传播轨迹，对两类波的传播路径完成了特征刻画。研究表明，尽管单次慢波事件可在全皮层几乎所有被探查位点起始，但绝大多数优先起始位点均位于大脑额叶区域，而波的终止则多倾向于后脑区与颞叶区域。