Casting light on sleep deficiency

摘要

There are many reasons why people get insufficient sleep in our 24/7 society, from early starts at work or school, or long commutes, to caffeine-rich food and drink. But the precipitating factor is an often unappreciated, technological breakthrough: the electric light. Without it, few people would use caffeine to stay awake at night. And light affects our circadian rhythms more powerfully than any drug. Just as the ear has two functions (hearing and balance), so too does the eye. First, rods and cones enable sight; and second, intrinsically photosensitive retinal ganglion cells (ipRGCs) containing the photo-pigment melanopsin enable pupillary light responses, photic resetting of the circadian clock, and other sightless visual responses. Artificial light striking the retina between dusk and dawn exerts other physiological effects through sightless vision. It inhibits sleep-promoting neurons and activates arousal-promoting orexin neurons in the hypothalamus, and suppresses the nightly release of the soporific hormone melatonin. These fac-