A new study solves a paradox that while gray matter declines in adolescence, there is also dramatic cognitive improvement from childhood to young adulthood.
In past studies of gray matter volume and cortical thickness, scientists found that gray matter — the tissue found in regions of the brain responsible for muscle control, sensory perception, such as seeing and hearing, memory, emotions, speech, decision making, and self-control — declines in adolescence. But scientists were puzzled that cognitive performance improved at the same that brain volume and cortical thickness decline.
A new study from researchers at the Perelman School of Medicine at the University of Pennsylvania reveals that while volume decreases from childhood to young adulthood, gray matter density actually increases.
The findings also show that while females have lower brain volume, proportionate to their smaller size, they have higher gray matter density than males, which could explain why their cognitive performance is comparable despite having lower brain volume.
While adolescents lose brain volume, and females have lower brain volume than males, this is compensated for by increased density of gray matter, the researchers explain.
“It is quite rare for a single study to solve a paradox that has been lingering in a field for decades, let alone two paradoxes, as was done by Gennatas in his analysis of data from this large-scale study of a whole cohort of youths,” said Dr. Ruben Gur, a professor of psychiatry, neurology, and radiology. He referred to the work of Efstathios Gennatas, M.B.B.S., a doctoral student of neuroscience working in the Brain Behavior Laboratory at Penn.
“We now have a richer, fuller concept of what happens during brain development and now better understand the complementary unfolding processes in the brain that describe what happens,” Gur said.
The study findings may better explain the extent and intensity of changes in mental life and behavior that occur during the transition from childhood to young adulthood, Gur noted.
“If we are puzzled by the behavior of adolescents, it may help to know that they need to adjust to a brain that is changing in its size and composition at the same time that demands on performance and acceptable behavior keep scaling up,” he added.
In the study, the researchers evaluated 1,189 youth between the ages of eight and 23 who completed magnetic resonance imaging as part of the Philadelphia Neurodevelopmental Cohort. The community-based study of brain development included neuroimaging and cognitive data to look at age-related effects on multiple measures of regional gray matter, including gray matter volume, gray matter density, and cortical thickness.
Observing such measures during development allowed the researchers to study the brain at different ages to characterize how a child’s brain differs from an adult’s.
“This novel characterization of brain development may help us better understand the relationship between brain structure and cognitive performance,” Gennatas said.
“Our findings also emphasize the need to examine several measures of brain structure at the same time,” he said. “Volume and cortical thickness have received the most attention in developmental studies in the past, but gray matter density may be as important for understanding how improved performance relates to brain development.”
The study was published in the Journal of Neuroscience.
Photo: MRI-derived gray matter measures, density, volume, mass, and cortical thickness, show distinct age and sex effects, as well as age-dependent intermodal correlations around adolescence. Credit: Penn Medicine.