Before Birth, Fetuses' Brains Are Probably Running on Idle

Even while our brains are at rest, they buzz with activity. A new study finds this activity develops by the time a fetus reaches full-term.

"Resting state activity" is what the brain engages in when it isn't working on a particular task. The neurons that carry out this background action are in networks all over the brain, from visual areas to motor areas to areas involved in attention and abstract thinking. One of these networks, the default mode network, engages when people are in a state of wakeful rest, leading researchers to theorize that the network is involved with daydreaming and introspection.

A study published today (Nov. 1) in the journal Proceedings of the National Academy of Sciences, finds that the default mode network is fully operational by birth. That suggests the network's role is more than for introspection alone, study researcher David Edwards said.

"Either babies are lying there introspecting — which is possible, although we can't remember it — or else this theory is a bit wrong," Edwards, a professor of neonatal medicine at Imperial College London, told LiveScience.

To peer inside the brains of infants, Edwards and his colleagues used functional magnetic resonance imaging (fMRI), a method that captures changes in blood flow throughout the brain. Increased blood flow brings more oxygen and correlates with brain activity.

The researchers carried out the brain scans on 70 healthy infants who had been born after 29 to 43 weeks of development. (Forty weeks is considered a full-term pregnancy). The researchers found that the resting state networks were completely developed in full-term babies. Babies born at 30 weeks development had incomplete but recognizable fragments of the networks, suggesting that resting state networks in infants develop within the last 10 weeks of pregnancy.

Once a fetus (or premature baby) is 40 weeks old, its network looks much like an adult's.

Previous studies had found fragments of these networks, but the new research used sensitive methods to uncover the entire system, the researchers wrote. The findings suggest that resting state networks are less involved with conscious action and thoughts than had been believed, Edwards said.

"They're more fundamental than has previously been thought, because they don't need to be related to any cognitive aspect," Edwards said. "They're very fundamental bits of brain activity and therefore very powerful to help us understand what the brain is really doing."

Edwards and his colleagues are now studying infants who have disrupted resting state networks, to find out if the disruption affects the babies' development.

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