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. 2012 Dec 21;13:153.
doi: 10.1186/1471-2202-13-153.

Increased Cerebral Blood Flow in the Right Frontal Lobe Area During Sleep Precedes Self-Awakening in Humans

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Free PMC article

Increased Cerebral Blood Flow in the Right Frontal Lobe Area During Sleep Precedes Self-Awakening in Humans

Sayaka Aritake et al. BMC Neurosci. .
Free PMC article

Abstract

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.

Figures

Figure 1
Figure 1
Experimental schedule. Subjects arrived at the sleep laboratory around 21:00 and were instructed to go to bed at 00:00 (lights off) after preperations were made to measure PSG and NIRS. Experiments under each of the two conditions were conducted twice for each subject in a consecutive two-night, single-blind crossover setting (“request” and “surprise”) without notice of which condition would be examined first. Each subject was randomly allocated to one of two conditions and instructed at bedtime to wake up at: 1) 03:00 (“request”); or 2) 08:00, but was unexpectedly woken at 03:00 (“surprise”). When the subject could self-awaken at 03:00 ± 30 min, the result was recorded as “success” or otherwise as “failure”. Each subject was examined under the other condition the following day.
Figure 2
Figure 2
Approximate positions of the 31 fNIRS channels superimposed on a head model. The 31 measuring channels were produced by optrodes placed equidistantly over the prefrontal cortex (PFC) area. The lower line of the 4 × 5 optrode probe was positioned along the reference curve linking C3, C4, Fz, and FPz. Red denotes source optrodes and blue denotes detector optrodes.
Figure 3
Figure 3
Change of oxy-Hb level during 30 min before waking in one “success” and one “failure” subject. Upper panel shows the gradual increase in oxy-Hb level in the right prefrontal region of a “success” group subject on the “request” night but not on the “surprise” night (A). In contrast, the oxy-Hb level showed no increase under either condition in the “failure” subject (B).
Figure 4
Figure 4
Change of oxy-Hb level and sleep structures during the final 30 min before waking (n=11). Temporal change in the oxy-Hb level (A), the rate of oxy-Hb levels (B), and temporal change δ power in the prefrontal cortex (PFC) region (C) during the final 30 min before waking in 11 subjects. The “request” condition and oxy-Hb level (change according to time course and the rate during the final 30 min before waking) in the right PFC (rPFC) region gradually increased 20 min before predominant waking in the “success” group (black circle) compared with the “failure” group (○) (A-1, B-1). The delta power of the “success” group also decreased in the rPFC region with time under the request condition (C-1).

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