Who doesn’t remember puberty? Cracking voice, hair growing in places where you never imagined them to grow, and above all, the realization that you have a libido. There are changes occurring not only physically, however, but chemically as well, in the brain’s circuitry. Penn Medicine researchers have discovered that before the onset of puberty, pre-puberty changes take place that result in decreased cerebral blood flow (CBF) to the brain. What’s surprising is that even though the rate of decreased CBF is similar in boys and girls, once they hit puberty the levels increase in girls while decreasing further in boys. These findings could give an insight to the different psychologies between men and women, and factors that lead to development of certain brain disorders that are sex-specific. "These findings help us understand normal neurodevelopment and could be a step toward creating normal growth charts for brain development in kids,” said Dr. Theodore D. Satterthwaite, assistant professor in the Department of Psychiatry in the Perelman School of Medicine at the University of Pennsylvania, in a press release. “These results also show what every parent knows: boys and girls grow differently. This applies to the brain as well. Hopefully, one day such growth charts might allow us to identify abnormal brain development much earlier before it leads to major mental illness." 

A number of neuroimaging studies looking at the development of the brain during stages of puberty have shown structural and functional differences between the sexes. Studies have shown that CBF rates, though high during infancy, gradually decrease during the onset of puberty. The exact cause for this is not known. The researchers know that adult women have higher rates of CBF than men. Since they were unsure of when the differentiation begins, they “hypothesized that the gap between women and men would begin in adolescence and coincide with puberty," Satterthwaite said.

 The researchers detected these changes in blood flow by imaging the brains of 922 people, ages 8 to 22, using arterial-spin labeled MRI. The youths were volunteers from the Philadelphia Neurodevelopmental Cohort. The results proved their theory. While the CBF was equal in both the sexes before puberty, there was a sharp change during puberty. It began around 16 years of age. While the CBF increased in females, it continued to decline in males throughout adolescence and into adulthood.  The difference in blood flow also depended on the location in the brain, and was most distinct in the orbitofrontal cortex, the part responsible for social behavior and emotional intelligence. These results could explain why women exhibit superior performance on social cognition tasks. The increased blood flow may also be the reason why women are more prone to depression and anxiety disorders.