Recent research has suggested that some parts of the brain can detect and respond to light, even without connections to the eyes. This intriguing process has been observed in animals as diverse as fish, birds, and mice, but the specific neurons and receptors involved were unknown.
To identify these neurons and receptors, researchers in the Unit on Behavioral Neurogenetics, within the Division of Intramural Research Program in Genomics of Differentiation, worked with the zebrafish, an animal that has been used for years to learn about developmental processes that are similar in all vertebrate animals, including humans.
The researchers studied several groups of zebrafish, including fish that had lost their eyes early in development and fish with genetic mutations that made them unable to produce certain light-sensitive proteins that have been found in the deep brain. Through a series of behavioral experiments in different light conditions, the researchers located cells in the deep brain that contained a light-sensitive pigment called melanopsin. With these cells present, fish in dark areas of a tank would wiggle until they ended up in a brighter area—even if the fish had no eyes.
This new information illuminates an ancient brain response that may have behavioral and developmental implications for many vertebrate animals (PMID: 23000151).