To investigate the effects of white and red light at 10?lx during the entire dark period on sleep and wakefulness, we examined the sleep–wake profiles of the mice exposed to 12-h white and red light at an intensity of 10?lx. Darkness exposure during the entire dark phase served as the control. We found that 10?lx white light exposure during the entire dark period significantly increased NREM and REM sleep for 2?h and that there was an increased tendency toward sleep in the subsequent hour, but this effect was not statistically significant when compared with the entire dark group . When the sleep amount during the 3?h after light exposure was calculated, the total amounts of NREM and REM sleep were also increased (Figure 6b). Moreover, white light at 10?lx disturbed the sleep–wake architecture. White light at 10?lx increased the stage transitions, the episode number for all stages, and the mean duration of REM sleep, as compared with darkness/red light at 10?lx . However, mice exposed to red light at 10?lx exhibited the same sleep–wake profiles as mice that stayed in darkness (Figure 6a and 6b). These findings clearly indicated that dim red light does not affect the sleep amount, whereas dim white light does. Furthermore, there were no differences between the groups of 10?lx red light and darkness in terms of episode number and mean duration, and stage transition number among NREM sleep, REM sleep and wakefulness (Figure 6c and 6d). These results demonstrated that 10?lx red light exposure during the entire dark period did not affect the amount or the architecture of sleep and wakefulness. Moreover, 12-h exposure of white and red light at 10?lx decreased the delta power activity of NREM sleep in the frequency range of 0.75–2.75 and 1.0–1.25?Hz within the first 3?h, as well as 0.5–2.25 and 0.5–1.0?Hz within the entire 12?h during the dark phase, respectively, compared with darkness. However, white light at 10?lx increased the power in the frequency ranges of 4.25–6 and 7.75–24.75?Hz within the first 3?h and of 4–5.25 and 7.5–24.75?Hz within the entire 12?h during the dark phase, as compared with darkness. In contrast, 12-h exposure of red light at 10?lx increased the power in the frequency range of 4.25–5.5?Hz within the first 3?h and of 4–5.25?Hz in the entire 12?h during the dark phase, compared with darkness (Figure 6e and 6f). These results indicated that 12-h exposure at 10?lx of both white and red light in the entire dark period influences the EEG power density.
Figure 6.
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Effects of 10?lx white or red light exposure for 12?h on sleep during the entire dark phase. (a) Time course changes in NREM sleep and REM sleep in mice exposed to 100?lx white light (WL) during the day and exposed to darkness, 10?lx WL and red light (RL) at night. Each cycle represents the hourly mean±SEM of NREM and REM sleep. Black, white and red circles indicate the profiles of darkness, white and red light treatments, respectively. The horizontal black, white and red bars on the x axes indicate darkness, white light and red light treatments, respectively. *P<0.05, **P<0.01 indicate significant differences between white light and darkness. #P<0.05, ##P<0.01 indicate significant differences between white light and red light. Data shown are assessed via two-way ANOVA followed by a Bonferroni test. (b) Total time spent in NREM sleep and REM sleep for 3?h after 10?lx white or red light treatment. Black, white and red bars show the profiles of darkness, white and red light treatments, respectively. indicates significant differences compared with darkness or to red light, respectively. Data were assessed via one-way ANOVA followed by a Bonferroni test. (c, d) Stage transition (c), episode number and mean duration (d) in a 3-h period after the treatment of 10?lx white or red light. Black, white and red bars show the profiles of darkness, white and red light treatments, respectively. *P<0.05, **P<0.01 indicate significant differences between two groups. Data were assessed via one-way ANOVA followed by a Bonferroni test. R, REM sleep; S, NREM sleep; W, Wake. (e, f), EEG power density of NREM sleep within the first 3?h (e) and the entire 12?h (f) during the dark phase. Values are means±SEM (n=5–8). Blue and red horizontal bars indicate the location of a statistically significant difference (P<0.05, two-tailed unpaired t-test) between white or red light and continuous darkness, respectively.
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