Brain cells start sending signals early

Fetal neurons show firing patterns similar to those seen in sleeping adults

The kicks and somersaults of a developing baby aren’t the only in utero calisthenics. Babies also flex their mental muscles months before birth.

Nerve cells from developing brains as young as 20 weeks old fire in a pattern that persists into adulthood, researchers report February 15 in the Journal of Neuroscience. The research provides a glimpse into the behavior of extremely young brain cells and could help scientists understand what happens when brain development goes awry.

Cells from the cerebral cortices of 20- to 21-week-old fetuses exhibit bursts of electrical activity interspersed with periods of quiet, researchers from the University of Connecticut Health Center in Farmington found. When the adult brain is sleeping, or under anesthesia, it also displays this busy-then-quiet firing pattern, suggesting it may be an intrinsic property of human brains.

The cerebral cortex deals with sensory information, thinking, emotion and consciousness. But even when not receiving input from the outside world, the nerve cells, or neurons, in this region oscillate between firing and resting.

“In adults, we go to sleep and the cortex is disconnected from the outside environment — it sleeps alone. But you see this quiet synchronized activity,” says Igor Timofeev of Laval University in Québec. That young nerve cells behave in a similar way long before they grapple with outside input suggests that the firing pattern “is a very basic feature of the brain that occurs in very early stages of development,” says Timofeev.

Scientists still don’t understand what purpose the nerve cell activity serves so early in development. Perhaps it is a flexing of mental muscles to help keep the cells alive, says neuroscientist Srdjan Antic, who led the new study. Having a burst of activity now and again may signal other brain cells that “‘Hey I’m here, look at me, maintain a connection with me,’” Antic says. “During sleep neurons do exactly that.”

Antic and colleagues probed the activity of neurons in lab dishes one at a time. While almost all of the cells exhibited the firing pattern, the team can’t say whether the firing was synchronized. If the cells do fire in waves, that could be their way of signaling their location to other brain cells, says neuroscientist William Moody of the University of Washington in Seattle.

Such wave signaling in mice brains plays a role in wiring the nervous system during development so that adjacent brain regions correspond to adjacent body parts. If these young cells are firing in waves, that activity could be part of this mapping process, Moody says.

“This is a huge deal,” he says of the new work. “They’ve taken the first step of looking at humans.”

There are several disorders that may result when neurons don’t end up in the right place. And autism spectrum disorders may also be related to improper firing, says Moody.

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