2023-05-08 05:20:00
Many of the traits that define us—such as the language we speak and the way we relate to others—go back, at least in part, to our earliest experiences. Although our brain is malleable throughout life, most neuroscientists agree that the changes that occur in utero and in the first years of life are the most important, since they greatly influence the risk of suffering from psychiatric and developmental disorders.
“Early in life, the brain is still forming,” says Claudia Lugo-Candelas, a clinical psychologist at Columbia University and co-author of a study on the prenatal origins of psychiatric illness published in the Annual Review of Clinical Psychology. Starting from a tiny group of stem cells, the brain becomes a complex organ of some 100 billion neurons and trillions of connections in just nine months. Compared to the more subtle brain changes that occur later in life, Lugo-Candelas says, what happens in the womb and shortly after birth “is like building the house, compared to just finishing the terrace.”
But exactly how this process unfolds and why it sometimes goes awry has been a difficult mystery to unravel, in large part because many of the key events are hard to observe. The first MRI scans of the brains of babies and fetuses were taken in the early 1980s, and doctors used this tool to diagnose major malformations in brain structure. But neuroimaging tools that can capture the inner workings of the baby’s brain in detail and spy on fetal brain activity in pregnant mothers are much more recent developments. Today, this research, along with long-term studies that follow thousands of children for years, offer scientists new insights into brain development.
These advances have propelled researchers into a different phase than they were even five years ago, says Damien Fair, a neuroscientist at the University of Minnesota who studies developmental disorders such as autism and ADHD. ).
Until recently, one of the main problems was that, unlike adults, fetuses and newborns did not stay still in brain scans. Powered by amniotic fluid, the fetus constantly changes position, and newborns love to squirm to observe their surroundings. In the past, researchers and doctors had to perform multiple expensive and time-consuming scans to get a good image. Children and pregnant mothers were sometimes sedated to reduce movement, a method that alters brain function and can pose health risks.
But new imaging and computing techniques that reduce distortions caused by motion — including software developed by a company Fair co-founded — have made it easier to get data from babies and fetuses. And that has revitalized the field of study.
A look at prenatal brain development
New work is beginning to reveal what typical brain development looks like and hints at how atypical disorders such as autism and ADHD may arise. In a groundbreaking 2017 study, for example, a team of researchers led by pediatric neuroscientist Moriah Thomason, now at New York University, used functional magnetic resonance imaging to investigate patterns of neural communication between the brain regions of 32 fetuses. . Half of the pregnant women were at high risk of preterm birth and 14 of the babies ended up being born prematurely.
Preterm birth is a known risk factor for later cognitive and emotional problems. But scientists have found it difficult to determine whether it is due to the trauma of preterm birth, which often involves brain injury and oxygen deprivation, or to pre-existing brain differences that begin in utero.
Thomason’s study provided the first evidence that problems start in the womb.
As fetuses, the soon-to-be preterms scanned by her team had brain activity that suggested weaker communication between various brain regions compared to fetuses that reached term. Most surprisingly, the scientists detected impaired neural communication in networks that will eventually become relevant to language, including a language center in the left side of the brain.
Since then, researchers have found more evidence of prenatal brain abnormalities in premature babies. In 2021, for example, another group found that 24 babies born prematurely had smaller brain volume and less spinal fluid while still in the womb, compared to a group of babies carried to term. And several studies have found that women who give birth prematurely have high levels of inflammation caused by bacterial or viral infections in the amniotic fluid and placental tissues.
The findings add to growing evidence that inflammatory events during pregnancy can alter fetal brain development. Studies of large populations, for example, have shown that mothers who have suffered a severe infection during pregnancy have a slightly increased risk of having an autistic child, although it is not yet clear that prenatal infection alone can cause autism.
Lugo-Candelas’ research focuses on how a pregnant woman’s perceived stress, life events, depression and anxiety can affect early brain development. Several studies have found that a high level of maternal anxiety and depression during pregnancy is associated with a two-fold increased risk of the child developing a mental disorder later in her life. If the risks start earlier in the development, “that also means that there is the possibility of intervening earlier than we thought,” says the expert. However, adds Lugo-Candelas, scientists continue to work to unravel the mechanisms underlying this increased risk, which stressors may have the greatest impact, and when and how to intervene.
Also, like many other risk factors in pregnancy, there is no single thing that causes psychiatric illness or developmental problems, says Lugo-Candelas. “It’s a set of small risks.” She stresses that there is nothing rigidly deterministic about any of these early exposures or experiences. “You can have children prenatally exposed to a lot of things that we think might increase the risk of psychiatric illness, and then have a child who doesn’t have a disorder and never will.”
This complexity reflects one of the biggest challenges in studying the developing brain: the fact that similar outcomes, such as autism or schizophrenia, can have many underlying neurological causes. For example, some people with autism have greater connectivity between certain brain regions than the neurotypical population, but others have less. There is no single neural pattern for this condition.
Brain connections as ‘neural fingerprints’
Fair has addressed this problem by identifying what he calls “functional fingerprints,” that is, uniquely individual patterns in the way different brain regions communicate with each other when a person is at rest inside an MRI scanner.
In 2014 he first observed these neural imprints in adults and later showed that children have them too. Fair and her team found that the patterns are surprisingly consistent within families, even across generations, suggesting that certain types of brain connectivity are at least partially inherited.
Last year he published evidence that even eight-month-old babies have these neural fingerprints, and that certain elements of the fingerprint, such as the amount of crosstalk between regions involved in functions such as attention and movement, can predict the exact age of a baby. baby, up to a few months.
Meanwhile, Thomason’s functional magnetic resonance imaging studies of the fetal brain suggest that these distinct connectivity patterns emerge in the second and third trimesters, including in neural circuitry that ultimately governs learning, memory, and emotion. Thomason and other researchers are using neuroimaging to study how various prenatal experiences—from maternal exposure to Covid to cannabis use—affect the development of these circuits.
The fact that scientists can detect these patterns of brain activity so early suggests to Fair and others that much of what makes us who we are is already in place by the time we’re born, even though we’ll continue to be shaped by it. by our experiences and exposures throughout life. However, since each baby’s brain is shaped by so many different factors, researchers are going to need long-term imaging data from thousands of children to get a solid understanding of what “typical” development looks like, Fair and her colleagues say. colleagues at the 2021 edition of Annual Review of Developmental Psychology.
Over time, diagnostic imaging tools could help doctors and researchers monitor a baby’s brain development, detect signs of future problems, and develop earlier personalized interventions and treatments for conditions like autism, Fair adds.
Meanwhile, Lugo-Candelas believes we already know enough to act. “I am confident that interventions that effectively minimize distress during pregnancy, such as paid maternity leave, will benefit the next generation,” she says. She points out that this could lead to better results in school and in other areas, such as mental health, that extend throughout life. “I don’t think we’ve done a good job yet of measuring what those outcomes look like or the mechanisms that lead to them.”
Article translated by Debbie Ponchner.
This article originally appeared on Knowable in Spanisha non-profit publication dedicated to making scientific knowledge available to everyone.
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