Scientists have provided unprecedented insights into how the activity of neurons in the brain changes during birth.
In a new study, researchers analyzed 184 brain scans collected from 140 fetuses and gestational-aged infants between 25 and 55 weeks after conception. A typical pregnancy lasts about 40 weeksSo these datasets gave researchers a good look at what the brain looks like before and after birth.
The analyzes revealed that the neuron activity in certain regions of the brain, increased significantly during birth. These regions include the sensorimotor networkwhich is responsible for processing external stimuli, such as images and sounds, and coordinating movements. They also include the subcortical network, which acts as a relay hub to obtain information from different regions of the brain.
After birth, babies are suddenly exposed to an enormous amount of sensory information from the outside world – often the beeps of hospital equipment, the smells of their parents and the lights shining on them. Their brains must be prepared and able to adapt to this noisy world beyond the womb. However, until now, little was known about how brain activity actually changes during birth, according to the authors of the new study published November 19 in the journal Biology PLOS.
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“Birth is the most important event in human life; it is a truly dramatic change from the in utero environment (in the womb) to the external environment,” Lanxin Jilead author of the study and a postdoctoral researcher at NYU Langone Health, told Live Science. “So there are a lot of changes throughout the body, including the brain.”
Over the course of a decade, Ji’s colleagues built a detailed dataset of fetal and infant brain scans using functional magnetic resonance imaging (fMRI). This technique indirectly measures brain activity by monitoring the amount of oxygenated blood circulating in the organ and therefore being used by neurons in different areas.
Typically, scientists perform an fMRI by placing a very still person inside a tube-shaped scanner. However, it is difficult to get a clear signal of brain activity in fetuses, especially since they move around a lot in the womb, Ji explained.
To overcome this challenge, the researchers scanned the fetuses’ brains using a soft magnetic coil that they placed directly on their mother’s abdomen. Then, they used various analysis techniques, including artificial intelligence (IA), to cancel out the effects of fetal movements. Once this noise was removed, they were able to reconstruct the neuronal activity taking place in the fetuses’ brains.
In addition to the effects seen in sensorimotor and subcortical networks, the researchers also noticed that brain activity increased significantly in the “higher frontal network” throughout birth. This network of connected brain areas regulates more complex cognitive skillssuch as working memorywhich allows people to remember things in the short term, such as when thinking about a math problem or following a set of directions.
“The change in the superior frontal cortex exceeds our expectations because we think the frontal lobe develops later during childhood,” Ji said. Further research is therefore needed to explain these new findings.
Notably, although the researchers observed a strong and significant increase in functional connectivity throughout birth, the efficiency of communication between these neurons increased much more gradually. In other words, the neurons were much more connected to each other, but an effective network still needed to be refined.
Researchers think the brain may need time to fine-tune its network structure to optimize its efficiency while removing unnecessary connections, a phenomenon known as synaptic pruning.
The researchers hope their new findings will serve as a basis for future research examining how environmental factors can influence brain development before and after birth. They now plan to compare the timing and growth of brain networks in premature babies — those born alive before 37 weeks — with those of full-term babies, to see if they differ in their early brain development, Ji said.
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