Placenta and Fetal Brain
Research is showing that the placenta is very important in filtering what passes from the mother through to the fetus (see O’Donnell and colleagues, 2009).
It seems that the emotional state of the mother can change this filtering capacity.
If the mother is stressed more of the stress hormone cortisol may pass through, and this in turn can alter the development of the fetal brain.
Cortisol is usually broken down by an enzyme called 11β-HSD2:
If the mother is stressed there is less of this enzyme in the placenta and so more cortisol can filter through and affect the development of the fetal brain.
There is also evidence that exposure to higher levels of cortisol in the womb can alter the development of the fetal brain (See Bergman and Colleagues 2010).
The Placenta and the Fetal Brain
The primary function of the placenta is to maintain an adequate supply of nutrients to fetus. This is especially important for fetal brain development which undergoes rapid growth in the prenatal period:
A 3mm neural tube will grow into a whole brain containing 100 billion neurons and 100 trillion connections.
Proliferation (production of new neurons) starts at 5 weeks continues through 18 months.
Precursor cells give rise to neurons which migrate to specific brain areas and differentiate to perform specialised functions.
New neurons form connections between one another, termed synaptogenesis.
An excess of neurons are produced prenatally. Neural pruning removes the unused neurons, a process which continues at least until puberty.
Although recent evidence has shown that new brain cells are formed well into adulthood, termed adult neurogenesis, the brain experiences the greatest growth before birth as shown in the figure below: