Asymmetric interhemispheric sigma waves during all-night sleep in humans

Abstract

There are some studies that have examined the asymmetry of brain function, such as that reflected in electroencephalogram (EEG) activity, during sleep, however, the results are not consistent. To clarify the asymmetry of brain function during sleep as well as cerebral dominance, period-amplitude analysis of sigma activity was performed on polysomnograms (PSGs) in normal humans. Fifteen healthy, male volunteers aged 22–34 years (mean age 27.4 years) participated in this study. Electroencephalograms were recorded from disc electrodes placed at bilateral frontal, central, parietal and occipital (10–20 electrode system) sites using A1 + A2 for reference. Period-amplitude analysis was performed by the zero-crossing method using the Medilog Sleep Analyzing Computer (Oxford Instruments, Oxford, UK). Sigma wave counts in the right frontal regions during all-night sleep were significantly greater than those in the left. To the contrary, sigma counts in the left parietal and occipital regions were significantly greater than those in the right. There were no significant regional differences and no significant difference between the left and right hemispheres in the total alpha counts during all-night sleep. There were significant regional differences in the total beta wave counts during all-night sleep. However, there was no significant difference in beta counts between the left and right hemispheres. These results suggest distinct laterality in the number of sigma waves in the frontal and parietal regions, reflecting functional asymmetry of the brain during sleep.