Bright light and social signals affect how human body clocks adjust differently

Seven of nine subjects showed an orthodromic phase shift in circadian rhythm under bright light conditions.

• The study assessed the reentrainment of human circadian rhythms under two conditions: with and without bright light.
• A significant phase shift in circadian rhythms was observed, with a larger shift occurring with bright light pulses.
• The maximum phase-advance shift occurred when bright light was applied approximately 4 hours after melatonin levels began to rise.
• Ordinary room light applied at the time corresponding to bright light also produced a similar maximum phase shift but at 1 hour after melatonin onset.
• Bright light and social schedules are associated with different effects on the reentrainment of circadian rhythms.

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