Researchers suggest that the act of birth causes a reduction in a particular brain chemical, triggering sensory maps in preparation for a newborn's survival outside the womb, according to a study published in the journal Developmental Cell.
Many mammals, including mice and humans, possess brain maps that represent a variety of sensory information, say the researchers from Japan.
In mice, a region of their brain called the barrel cortex contains neurons responsible for processing information from the whiskers when they experience the sense of touch.
These neurons are arranged in a "map," which corresponds to the spatial pattern of the whiskers on the snout, while columns of neurons next to those in the barrel cortex respond to the simulation of adjacent whiskers.
Previous studies have shown that a neurotransmitter called seratonin plays a part in influencing the development of these sensory maps. However, seratonin's specific role in the development of sensory maps has been unclear.
For the study, the researchers analyzed the levels of seratonin in the brains of newborn mouse pups.
Birth 'reduces seratonin levels'
They found that the act of birth led to a significant drop in seratonin. This triggered the formation of neuronal circuits in both the barrel cortex and the lateral geniculate nucleus (LGN) - a region of the brain responsible for processing visual information.
When the researchers treated mice with drugs that either induced preterm birth, or decreased seratonin signaling, they found that neural circuits in both the barrel cortex and LGN formed faster.
However, when the mice were treated with drugs that increased seratonin signaling, the neural circuits did not form. The researchers say this suggests that reduction in seratonin levels is critical for sensory map formation.
Hiroshi Kawasaki, of Kanazawa University in Japan and senior study author, explains:
"Our results clearly demonstrate that birth has active roles in brain formation and maturation.
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."
Potential increased risk of mental disorders
Seratonin, also known as 5-hydroxytryptamine, is known to play a part in the regulation of learning, mood, sleep and vasconstriction - the constriction of blood vessels.
The researchers note that their findings suggest that abnormalities in the birth process, and the effects these may have on seratonin signaling and brain development, could lead to increased risk of psychiatric disorders.
"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 diseases induced by abnormal birth," Kawasaki says.
Earlier this year, Medical News Today reported on a study on epigenomic maps that set out how brain circuits change from birth to adulthood.