According to a new Penn Medicine study, brain development does not occur uniformly across the brain, but rather follows a newly identified developmental sequence. Throughout adolescence, brain regions that support cognitive, social, and emotional functions appear to remain more capable of changing, adapting, and remodelling than other brain regions, making adolescents more sensitive to socioeconomic environments.
Using magnetic resonance imaging (MRI), researchers mapped the development of the human brain between the ages of eight and twenty-three. The findings suggest a novel method for understanding the sequence in which plasticity decreases in different brain regions during development.
Brain plasticity refers to the ability of neural circuits — connections and pathways in the brain for thought, emotion, and movement — to change or reorganize in response to internal biological signals or the external environment. While it is widely assumed that children have more brain plasticity than adults, this study sheds new light on where and when plasticity declines in the brain during childhood and adolescence.
Human Higher-order Thinking Regions
The findings show that reductions in brain plasticity occur first in sensory-motor regions like visual and auditory regions, and later in associative regions like those involved in higher-order thinking (problem solving and social learning). As a result, while plasticity occurs later in development, brain regions that support executive, social, and emotional functions appear to be particularly malleable and responsive to the environment during early adolescence.
“Studying brain development in the living human brain is challenging. A lot of neuroscientists’ understanding about brain plasticity during development actually comes from studies conducted with rodents. But rodent brains do not have many of what we refer to as the association regions of the human brain, so we know less about how these important areas develop,”
said corresponding author Theodore D. Satterthwaite, MD.
To address this issue, the researchers focused on comparing findings from previous rodent studies to findings from youth MRI imaging. Previous research on how neural circuits behave when they are plastic revealed that brain plasticity is associated with a distinct pattern of “intrinsic” brain activity.
Intrinsic Neural Activity
Intrinsic activity is neural activity that occurs in a part of the brain when it is not engaged by external stimuli or a mental task. When a brain region is less developed and more plastic, there is more intrinsic activity within the region, which is also more synchronized.
This is due to the fact that more neurons are active in the region, and they tend to be active at the same time. As a result, amplitude measurements of brain activity waves show an increase (or height).
“Imagine that individual neurons within a region of the brain are like instruments in an orchestra. As more instruments begin to play together in synchrony, the sound level of the orchestra increases, and the amplitude of the sound wave gets higher,”
said first author Valerie Sydnor.
The amplitude of intrinsic brain activity can be measured with functional MRI while children are simply resting in the scanner, just as decibel meters can measure the amplitude of a sound wave. This enabled the researchers to study a functional marker of brain plasticity in children in a safe and non-invasive manner.
Environmental Influence Window
The authors discovered that the functional marker of brain plasticity declined in early childhood in sensory-motor regions but did not decline until mid-adolescence in associative regions after analyzing MRI scans from over 1,000 people.
“These slow-developing associative regions are also those that are vital for children’s cognitive attainment, social interactions, and emotional well-being. We are really starting to understand the uniqueness of human’s prolonged developmental program,”
Satterthwaite said.
“If a brain region remains malleable for longer, it may also remain sensitive to environmental influences for a longer window of development. This study found evidence for just that,”
Sydnor said.
Shaping Neurodevelopmental Trajectories
The authors investigated the connections between youths’ socioeconomic environments and the same functional marker of plasticity.
They discovered that the effects of the environment on the brain were neither uniform across regions nor consistent throughout development. Rather, as the identified developmental sequence progressed, the effects of the environment on the brain changed.
Critically, youths’ socioeconomic environments had a greater impact on brain development in late-maturing associative brain regions, with the greatest impact during adolescence.
“This work lays the foundation for understanding how the environment shapes neurodevelopmental trajectories even through the teenage years,”
said co- author Bart Larsen.
The researchers hope that studying developmental plasticity will aid in determining when environmental enrichment programs will benefit each child’s neurodevelopmental trajectory. Their findings support the notion that programs to reduce disparities in youths’ socioeconomic environments are important for brain development throughout adolescence.
Reference:
- Sydnor, V.J., Larsen, B., Seidlitz, J. et al. Intrinsic activity development unfolds along a sensorimotor–association cortical axis in youth. Nat Neurosci 26, 638–649 (2023).
Last Updated on September 20, 2023