Increased cerebral blood flow in the right frontal lobe area during sleep precedes self-awakening in humans

Background: Some people can subconsciously wake up naturally (self-awakening) at a desired/planned time without external time stimuli. However, the underlying mechanism regulating this ability remains to be elucidated. This study sought to examine the relationship between hemodynamic changes in oxyhemoglobin (oxy-Hb) level in the prefrontal cortex and sleep structures during sleep in subjects instructed to self-awaken.Results: Fifteen healthy right-handed male volunteers with regular sleep habits participated in a consecutive two-night crossover study. The subjects were instructed to wake up at a specified time (" request" condition) or instructed to sleep until the morning but forced to wake up at 03:00 without prior notice (" surprise" condition). Those who awoke within ± 30 min of the planned waking time were defined as those who succeeded in self-awakening (" success" group). Seven subjects succeeded in self-awakening and eight failed.No significant differences were observed in the amounts of sleep in each stage between conditions or between groups. On the " request" night, an increase in oxy-Hb level in the right prefrontal cortex and a decrease in δ power were observed in the " success" group around 30 min before self-awakening, whereas no such changes were observed in the " failure" group. On the " surprise" night, no significant changes were observed in oxy-Hb level or δ power in either group.Conclusions: These findings demonstrate a correlation between self-awakening and a pre-awakening increase in hemodynamic activation in the right prefrontal cortex, suggesting the structure's contribution to time estimation ability.