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Scientists Identify Why Girls Often Mature Faster Than Boys

Brain connections generally become streamlined earlier in girls than in boys.

Key points

  • Across large data points, there appear to be general differences in brain development between male and female cohorts.
  • Modern pressures make it difficult for the young human brain to form optimal connections during adolescence, and boys are especially vulnerable.
  • Parenting programs can help parents and children at all risk levels avoid adolescent behavior problems.

Scientists at Newcastle University in the U.K. have discovered that girls tend to optimize brain connections earlier than boys. The researchers conclude that this may explain why females generally mature faster in certain cognitive and emotional areas than males during childhood and adolescence. The new study was published on December 19, 2013, in Cerebral Cortex.

Of course, anyone who has read Middlesex knows that gender identification can be on a spectrum. Making generalizations about differences in brain structure based on being a "boy" or a "girl" can be a slippery slope. That said, scientists are trying to solve the puzzle of why across larger data points there appear to be general differences between brain development among male and female cohorts.

Whether you are male, female, or intersex, the brain undergoes a major restructuring during childhood. The connections in the brain that are not used regularly tend to shrink and evaporate due to lack of use—while the neural networks that are regularly engaged are nourished and survive. This is called “fire and wire” and it's the ultimate "use it or lose it" example of "neural Darwinism" and survival of the fittest among neural networks.

Optimizing brain connectivity is designed to give each human the best tools for survival in their environment. Unfortunately, in the modern world, many of these highly fine-tuned connections are short-circuiting due to neurobiological disorientation. The human brain cannot evolve fast enough to keep pace with the future shock of being born in the 21st century.

Many young people—especially boys—are vulnerable to the changes of growing up in a digital age. They become isolated and are thrown into a constant state of cortisol-fueled fight-or-flight. This wreaks havoc on a young and vulnerable brain that needs to be in a parasympathetic state of "tend-and-befriend" to feel safe.

I am a big fan of Amy Poehler’s “Smart Girls at the Party," geared toward adolescent girls and young teens with the mission to "celebrate individuals who are changing the world by being themselves." I believe that young boys and girls from all walks of life and gender identities can benefit from this message. As the father of a 6-year-old, I appreciate the message of self-empowerment being sent to children.

Environmental pressures like needing to perform well on standardized tests, a lack of physical activity, social disconnection, a constant stream of digital media, excessive screen time, potential ADHD medications, and poor nutrition conspire to make it difficult for the young brain to form optimal connections during adolescence. Again, it seems that young boys are especially vulnerable to short-circuiting without the physical outlets they have evolved to need over millennia.

Children are not designed to sit in a chair all day cramming for an exam. It seems possible that some boys might really need to run wild, and be more physically active (as do many girls).

Neural Pruning and Neural Plasticity Are a Dynamic Duo

In their new study, researchers led by Marcus Kaiser and Sol Lim at Newcastle University found that while overall connections in the brain get streamlined, long-distance connections that are crucial for integrating information are preserved in healthy people of both sexes, and there are dramatic gender differences at earlier stages of development.

The concept of neural Darwinism reinforces habits of thinking and habits of action. Sol Lim explained the importance of neural pruning: “The loss of connectivity during brain development can actually help to improve brain function by reorganizing the network more efficiently. Say instead of talking to many people at random, asking a couple of people who have lived in the area for a long time is the most efficient way to know your way. In a similar way, reducing some projections in the brain helps to focus on essential information.”

Kaiser adds, “Long-distance connections are difficult to establish and maintain but are crucial for fast and efficient processing. If you think about a social network, nearby friends might give you very similar information—you might hear the same news from different people. People from different cities or countries are more likely to give you novel information. In the same way, some information flow within a brain module might be redundant whereas information from other modules, say, integrating the optical information about a face with the acoustic information of a voice, is vital in making sense of the outside world."

This study showed how brain connectivity changed during development in terms of fiber tracts within brain regions and between brain regions. More specifically, the researchers found preferential decreases in the number of streamlines for thick, short-distance connections within both a brain region and a cerebral hemisphere. These changes may not necessarily occur at the same time for males and females: Males tend to show a delayed start from the prolonged development in white matter and gray matter.

The researchers demonstrated for the first time that the loss of white matter fibers between brain regions is a highly selective process—a phenomenon they call "preferential detachment."

However, they found that not all projections (long-range connections) between brain regions are affected to the same extent for males and females: Changes were influenced differently depending on the types of connections. Changes in these connections have been found in many developmental brain disorders including autism, epilepsy, and schizophrenia. With many neurological diseases, there are widespread differences between the sexes. For example, autism spectrum disorders are almost 5 times more common among boys (1 in 54) than among girls (1 in 252).

The results of another study—“Widespread Sex Differences in Gene Expression and Splicing in the Adult Human Brain”—were published on November 22, 2013, in Nature Communications. These authors found that sex-biased gene expression in the adult human brain tends to be widespread statistically. Most important, they found that in some cases, “Molecular differences are likely to have functional consequences relevant to human disease, and that sex biases in expression may reflect sex-biased gene regulatory structures.”

Conclusion: Toward Optimal Brain Connectivity for Every Gender Throughout the Lifespan

An interview with Jane Fonda from a few years ago at the Omega institute called “Our Sons” recently went viral. In the Q & A with Eve Ensler, Jane Fonda speaks of gender differences and the importance for parents and grandparents doing their best to keep young boys in touch with their emotions and able to form close-knit intimate connections. Research continues to mount which shows that brain connectivity tends to vary between the sexes. Personalized attention needs to be given to young boys early on to optimize healthy neural pruning and plasticity. That said, young girls obviously should be encouraged to break stereotypes of gender roles.

What can we do as parents to create an environment that nurtures optimal brain development for our sons, daughters, and anyone who feels intersex? In a recent post, I cited another study—“Promising Parenting Programmes for Reducing Adolescent Problem Behaviours,” published in the Journal of Children's Services on December 16, 2013. In it, University of Washington researchers identified five effective parenting programs to help reduce problem behaviors during the teenage years that can have repercussions for the rest of a person's life.

Parenting programs can help parents and children at all risk levels avoid adolescent behavior problems that affect not only individuals but entire communities. "With these programs, you see marked decreases in drug use, reduced aggression, reduced depression and anxiety, and better mental health," said Kevin Haggerty, assistant director of UW's Social Development Research Group in the School of Social Work.

"All of us need a little help parenting," Haggerty added. "It's a tough job and we didn't get the instruction manual." The programs recommended by Haggerty and his co-authors are effective with a wide range of families from diverse demographics. They all are based on the Social Development Model, which focuses on fostering opportunities, skills, rewards for positive social behaviors, bonding, and clear expectations for behavior.

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