Nerve impulses start to appear in fetal brain cells about 24 weeks into pregnancy – before that neurons might be too immature to respond to an external stimulus, according to a new study by Chinese scientists.
The researchers said the study presented unprecedented details about fetal brain development but cautioned that the neural signals should not be defined as “consciousness”.
Some parents believe that “fetal education” can make their children smarter by reading classical literature, playing music or simply speaking to the unborn child. A few studies suggested that the fetus could even tell the difference between Queen and Adele.
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But when the fetus had the ability to respond to these attempts remained unclear, and some scientists questioned if these reactions meant anything. “The fetus is almost continuously asleep and unconscious,” said Swedish paediatrician Hugo Lagercrantz in a paper published in the journal paediatric Research in 2009.
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Studying the brain development of a living fetus could help answer this question but this has been a challenge because it is impossible to access their brain directly.
With the approval of a hospital ethics committee in Beijing, a group of researchers led by Professor Wang Xiaoqun at the Institute of Biophysics at the Chinese Academy of Sciences studied intact brains from aborted embryos and fetuses donated by their parents for scientific research.
They retrieved tissues from different parts of the brains, recorded their responses to artificial stimulation and conducted genetic analysis on various types of brain cells in different stages of brain development.
The first neurons capable of sending nerve signals appeared in the frontal lobe of the cerebral cortex, according to their study published in journal Science Advances last week. Such active neurons did not show up in other parts of the brain until later, suggesting that development is not even across the brain, and the frontal lobe, which affects personality and communication, is a higher priority.
Through genetic sequencing, the researchers found out why the cells could only send nerve signals after the 24th gestational week.
They determined that it was only at that point that some genes regulated metallic ions such as sodium and potassium started to function, creating potential electric fields to allow the generation and passage of nerve signals.
“There have been many similar studies before, particularly in the US back in the 1970s, but our research has come up with some new discoveries, with unprecedented details and more definite timeline,” Wang said on Tuesday.
Wang said the presence of a nerve impulse did not necessarily mean consciousness in the fetus, given that “there is not a generally accepted definition of consciousness itself”.
Parents should also not mark week 24 on the calendar as anything special, he added. In the study, they also found a previously unknown boost to brain cell growth in week 14. That means “brain development undergoes many different stages, and every one of them is important”, he said.
The researchers said that studying the early development of the human brain could help find treatment for some brain diseases, but ethical concerns limited how far they could go.
For instance, during the study they discovered a gene that controlled the generation of oRG, a type of brain cell found in humans and primates but not other animals. Expressing the gene in mice significantly increased the size of the brain in the animal.
“That’s where we stopped,” Wang said.
“Giving animals human-like intelligence is one of those lines that we don’t want to cross.”
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This article The moment when the fetus sends its first nerve signals first appeared on South China Morning Post