Babies in the Womb May See More Than We Thought

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BERKELEY, Calif.—By the second trimester, long before a baby’s eyes can see images, they can detect light. 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 percent 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 with 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.

“Given the variety of these ganglion cells and that they project to many different parts of the brain, it makes me wonder whether they play a role in how the retina connects up to the brain,” said Marla Feller, a UC Berkeley professor of molecular and cell biology and senior author of a paper that appeared this month in the journal Current Biology. “Maybe not for visual circuits, but for non-vision behaviors. Not only the pupillary light reflex and circadian rhythms, but possibly explaining problems like light-induced migraines, or why light therapy works for depression.”

The research was supported by the National Institutes of Health.