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Sci Tech
Make light of jet lag
CELLS THAT help pick out day from night have been discovered lurking at the back of the eye, says a report in New Scientist.
These special cells use light to help set the body's internal clock, even in blind animals.
The cell doesn't care about contrast or colours, says David Berson of Brown University in Rhode Island. "It's almost like the light meter in your camera."
The finding is striking because the dogma for more than a hundred years was that there are only two kinds of light-sensing cells in the eye: the rods and the cones. Some suspected a third kind existed to record light intensity, but no one had been able to pin them down.
Berson and his team have identified this mysterious photoreceptor as a type of retinal ganglion cell.
These extend long projections into the brain to transmit information from the eyes by isolating ganglion cells in rats and exposing them to light.
Berson's group showed that a tiny fraction of specialised ganglia react by sending a signal into the region of the brain that regulates the circadian clock — the key to the body's sleeping cycle.
They suspect the cells use a unique pigment called melanopsin to do this.
Berson says it's very likely that these cells play the same role in humans, and are involved in controlling the release of the sleep-inducing hormone melatonin.
This might mean you could stimulate the ganglion cells with specific wavelengths of light to help reset people's internal clocks and cure problems like jet lag, he says.
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