Using MEG to Understand the Progression of Light Sleep and the Emergence and Functional Roles of Spindles and K-Complexes
Frontiers in Human Neuroscience June 16, 2017 A. Ioannides, Lichan Liu, V. Poghosyan et al.
During the transition to sleep, the brain actively inhibits frontal lobe activity, increasing delta and theta waves, while suppressing activation in the posterior parietal cortex, causing a sharp drop in alpha and higher frequencies. These changes may causally link to loss of consciousness. In light sleep, these patterns become more widespread, but alpha and low sigma power reemerge in frontal midline areas, suggesting some monitoring of internal and external environment resumes. Just before spindles and K-complexes, focal spectral changes occur in prefrontal cortex and anterior cingulate areas. Spindles involve further frontal inhibition and power increases in posterior parietal cortex, supporting memory consolidation. K-complexes correlate with alpha increases in monitoring areas, suggesting a sentinel role to evaluate provoking events and decide whether to wake or inhibit processing.