In addition, the cells tend to react to light in groups. Electrically, some of the cells work almost like a chorus, sending several synchronized "harmonies" to the brain as part of one big "song" that responds to light impulses.
"We were able to detect about 20 percent of the ganglion cells were coupled to other ganglion cells," he says. "That's probably a low estimate because if we had a finer grid and could record the activities of more individual cells, we might well find more interactions."
Van Gelder believes the early activity and the interactions of the ipRGCs may somehow enhance survival by helping animals detect light and set their circadian clocks prior to the development of vision. And he says because retinas tend to be very similar in most mammals, human ganglion cells also may develop and begin to function earlier than rods and cones.
Although ipRGCs sense light in mice and humans, they don't connect to the brain's visual cortex. Instead, they send signals to deeper, more ancient parts of the brain, such as the hypothalamus, from which they project to the brain regions that control the circadian clock as well as the response of the pupil to light.
"The multi-electrode array technique that Dan Tu and Don Zhang have brought into this field should help us learn a lot more about how these retinal ganglion cells influence all kinds of non-visual functions and reinforce the fact that the eye is responsible for more than just vision," Van Gelder says.
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Contact: Jim Dryden
jdryden@wustl.edu
314-286-0110
Washington University School of Medicine
21-Dec-2005