Hidden Organ in Our Eyes Found to Control Circadian Rhythms and Emotions

Our bodies adjust to the cycle of day and night thanks to specialized neurons in our eyes. Ongoing study of these cells could lead to new treatments for winter depression and other conditions

By Ignacio Provencio  | Monday, May 9, 2011 

Many years later researchers extended Keeler’s observation, showing that mice genetically engineered to lack rods and cones (the light receptors involved in vision) nonetheless reacted to changes in light by adjusting their circadian clock—the internal timer that synchronizes hormone activity, body temperature and sleep. The animals performed the usual daytime activities when in daylight and nighttime activities when in the dark. They could do so even though their retinas lacked the photoreceptor cells that vertebrate eyes use to form images, although surgically removing their eyes abolished this ability. This phenomenon may be common to many mammals, including humans: recent experiments have shown that certain blind people can also adjust their circadian clocks and constrict their pupils in response to light.

© 2011 Scientific American, a Division of Nature America, Inc.