Birth Prepares the Newborn Brain to Sense the World with Sensory Maps

A lot of things happen during birth. Chemical processes change in the brain as children travel through the birth canal. Now, scientists have discovered that the actual act of birth in mice causes a reduction in a brain chemical called serotonin. This triggers sensory maps to form, which prepares the mice to sense the world and prepares mice for survival outside the womb.

Mammals ranging from mice to humans have brain maps that represent various types of sensory information; for example, there's the sense of touch and vision that are arranged with neurons. When it comes to mice, though, there's a region of the brain known as the barrel cortex which consists of neurons that process tactile information from whiskers that are arranged in a map corresponding to the spatial pattern of whiskers on the snout. There are neighboring columns of neurons that also respond to the stimulation of adjacent whiskers. Although previous studies have shown that the neurotransmitter serotonin influences the development of sensory maps, its specific role during normal development has not been clear until now.

In this latest study, though, scientists have found out a little bit more about serotonin. They discovered that the birth of mouse pups leads to a drop in serotonin levels in the newborn's brain. This triggers the formation of neural circuits in the barrel cortex and in the lateral geniculate nucleus (LGN), a brain region that processes visual information. The scientists also found that when the mice were treated with drugs that induced preterm birth or decreased serotonin signaling, the neural circuits formed more quickly.

"Our results clearly demonstrate that birth has active roles in brain formation and maturation," said Hiroshi Kawasaki, one of the researchers, in a news release. "We found that birth regulates neuronal circuit formation not only in the somatosensory system but also in the visual system. Therefore, it seems reasonable to speculate that birth actually plays a wider role in various brain regions."

In fact, learning about serotonin might help treatments in the future. Serotonin plays a key role in mental disorders, which means that it's possible that abnormalities in birth processes and the effects on subsequent serotonin signaling and brain development could increase the risk of psychiatric diseases.

"Uncovering the entire picture of the downstream signaling pathways of birth may lead to the development of new therapeutic methods to control the risk of psychiatric disease induced by abnormal birth," said Kawasaki in a news release.

The findings are published in the journal Developmental Cell.