Meghan Bialt-DeCelie – ’19

Rapid modernization has had an impact on the hours that humans are active, disrupting natural and established rhythms. A team led by Anne Skeldon, PhD, developed a mathematical model that shows the effect of factors like artificial light on the human circadian rhythm and sleeping habits.

The mathematical model included three factors involved in sleep regulation: mutual inhibition of wake and sleep related neurons, internal circadian rhythm, and external light source that may disrupt the circadian clock. The model predicted that conditions that hunter-gatherers experienced, including no artificial light, allowed humans to sleep 2-4 hours after sundown and wake up an hour before sunrise, averaging around 7.7 hours of sleep. Socially driven changes in sleep schedules like changes in work or school schedules to fit one’s circadian rhythm may not be effective, as the rhythm will likely shift especially if habits with late night artificial light exposure remain the same. Overall, exposure to light during dark hours can significantly impact circadian rhythm. Without late night artificial light the model predicts one would wake naturally before a 7:00 AM alarm. However, with access to light late at night can impact by causing the natural rhythm to shift leading to a later sleep time and natural awakening to occur after the alarm.

The study is limited in that it does not consider several other environmental factors such as seasons, types of light wavelengths, or active decision making to change sleep schedules. The model does, however, show how rapid change in light exposure types, patterns, and durations can affect one’s sleep habits.

Sources:

1. M. Jha, et. al. Can C-reactive protein inform antidepressant medication selection in depressed outpatients? Findings from the CO-MED trial. Psychoneuroendocrinology78, 105-113 (2017). Doi:10.1016/j.psyneuen.2017.01.023
2. Image retrieved from: https://commons.wikimedia.org/wiki/File:4_day_trip_to_La_Selva_Lodge_on_the_Napo_River_in_the_Amazon_jungle_of_E._Ecuador_-_spectacular_last_night_sunset_on_Garzacocha_Lake_-_(26866317805).jpg