Babies in the Womb May See More Than We Thought
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But the light-sensitive cells in the developing retina -- the thin sheet of brain-like tissue at the back of the eye -- were thought to be simple on-off switches, presumably there to set up the 24-hour, day-night rhythms parents hope their baby will follow.
University of California, Berkeley, scientists have now found evidence that these simple cells actually talk to one another as part of an interconnected network that gives the retina more light sensitivity than once thought, and that may enhance the influence of light on behavior and brain development in unsuspected ways.
In the developing eye, perhaps 3% of ganglion cells -- the cells in the retina that send messages through the optic nerve into the brain -- are sensitive to light and, to date, researchers have found about six different subtypes that communicate with various places in the brain. Some talk to the suprachiasmatic nucleus to tune our internal clock to the day-night cycle. Others send signals to the area that makes our pupils constrict in bright light.
But others connect to surprising areas: the perihabenula, which regulates mood, and the amygdala, which deals with emotions.
In mice and monkeys, recent evidence suggests that these ganglion cells also talk with one another through electrical connections called gap junctions, implying much more complexity in immature rodent and primate eyes than imagined.
[...] The researchers also found evidence that the circuit tunes itself in a way that could adapt to the intensity of light, which probably has an important role in development, Feller said.
"In the past, people demonstrated that these light-sensitive cells are important for things like the development of the blood vessels in the retina and light entrainment of circadian rhythms, but those were kind of a light on/light off response, where you need some light or no light," she said. "This seems to argue that they are actually trying to code for many different intensities of light, encoding much more information than people had previously thought."
Journal Reference:
Franklin Caval-Holme, Marla B. Feller. Gap Junction Coupling Shapes the Encoding of Light in the Developing Retina. Current Biology, 2019; DOI: 10.1016/j.cub.2019.10.025
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