["Microcyclic" changes in brain bioelectrical activity during different stages of human natural sleep]

This study presents data on some phasic EEG phenomena regulary recorded during sleep - wakefulness cycle and heterogeneity of EEG sleep stages forming consecutive human sleep macrocycles. These short-term EEG changes quite often tend to periodization, especially during initial sleep-stages and transitive states (sleep microcycles). An attempt was made to reveal EEG microstructures in sleep - wakefulness cycle on the basis of 7 clusters reflecting changes in the biopotential field of the brain represented in n-dimensional factorial space. It was found that most sleep stages were presented by 3-4 clusters, but some sleep periods (such as B (Loomis, 1937) and IREM) showed more homogeneous structure. It was suggested that the heterogeneity of the EEG spatial organization within sleep stages reflect the dynamics of neurophysiological processes underlying reparative and homeostatic sleep functions.