Our sleeping pattern follows a circadian rhythm, which is really just a way of saying a daily pattern of wakefulness and sleepiness (circadian derived from Latin: circa – “about” and diem– “day”). Our circadian rhythm is influenced by environmental factors, known as zeitgebers (German for “time-givers”) which help to set this internal clock.
One of the most most powerful zeitgebers is light. When light hits your retina, messages are not only sent to the occipital lobe for visual processing, they are also sent to the suprachiasmatic nucleus, an area of the hypothalamus. In the presence of light (especially wavelengths corresponding to blue light), the suprachiasmatic nucleus inhibits the pineal gland from releasing melatonin into the bloodstream. Melatonin is a hormone which, when released into the bloodstream, causes us to feel drowsy. Through this process of inhibiting melatonin release, light helps to keep us feeling alert, while darkness helps bring drowsiness.
This process probably worked quite well in setting our circadian rhythm for millions of years of our evolutionary history, but the ubiquity of artificial light in most of our lives today may be interrupting this system. While our ancestors only really had bright light from the sun, we can have bright light any time we want. The darkness of dusk that told our ancestors to unwind and stay in the safety of shelter now simply signals us to turn on the lights.
If you have trouble falling asleep at night, light may be part of the problem and limiting your exposure to it in the evening may help you to fall asleep more easily. You may even consider using blue-light blocking glasses in the evening or downloading programs like f.lux which reduce the amount of blue-light emitted by your laptop or phone screen after sunset.
Light is not the only zeitgeber that influences our level of alertness. The timing of our meals, the ambient temperature, and our social interactions also play a role in the circadian rhythm. This may explain how you managed to stay awake all night at slumber parties and why it’s so easy to fall asleep in a warm room while a lecturer drones on and on without any chance of interaction.
The settings of this internal clock also vary with age, as teenagers tend to be “night-owls” whose concentration and attention peak later in the day or evening, while older adults tend to be “larks” who perform best in early morning, then decline as the hours go by. This is clearly seen in the classic class-time conundrum, as adults (parents and teachers) set the times that work best for them, while teenagers are alert at 11pm but stumbling and slumbering through early morning classes.
This post is an excerpt from Master Introductory Psychology: Complete Edition
