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- The brain develops through distinct phases over the course of a lifetime, says a new study.
- During each of these phases, the brain’s capacity for reorganization and forming new connections changes.
- The most efficient of these phases is adolescence, which, according to the study, begins at 9 and lasts until age 32.
There are five distinct eras, or epochs, in the lifespan of a human brain, according to a new study from researchers at the University of Cambridge in the United Kingdom, published in Nature Communications.
Separating these epochs are four turning points in the development and behavior of the brain that occur at the ages of 9, 32, 66 and 83.
The study tracks changes in the brain’s organization and elasticity — its ability to continue to rewire itself by creating new synaptic neural connections as needed.
What are the 5 stages of the brain’s evolution?
The five stages of a brain’s life described by the study are:
- Childhood, from birth to the age of 9. During childhood, the brain is continually pruning away haphazardly created synaptic connections forged as early learning, unlearning, and relearning chaotically occurs. As a result, while it is a time of rapid growth, it is not a time of great efficiency.
- Adolescence, from age 9 until about age 32. The study is unique in considering adolescence to be a period that extends to age 32. Adolescence is the most efficiently elastic time for a person’s brain, a time when new synaptic connections are most easily formed. Mental disorders are also most likely to begin during the adolescence epoch.
- Adulthood, from age 32 to age 66, the longest of the epochs. In adulthood, brain efficiency slows way down, says the study. At the same time, this is typically a period of maximum stability.
- Early aging, from 66 to 83 years of age. The study finds that patterns within the brain begin to shift during this era, with regions interoperating more tightly together, while the brain may begin operating less cohesively as a whole. It is also a time during which dementia and systemic issues such as cardiovascular problems are more likely to begin appearing.
- Late aging, from 83 and beyond. This period is similar to early aging, but changes are likely to occur at an accelerated pace.
The study’s findings are based on an analysis of diffusion imaging brain scans — diffusion imaging is a form of magnetic resonance imaging (MRI). They were conducted with 4,216 people, aged from infancy to 90 years of age.
How can we understand the 5 eras of the human brain?
Luis Goicouria, PhD, a senior researcher and developer at Attached, who was not involved in the study, spoke to Medical News Today about its findings.
To understand the characteristics that change through the five epochs, Goicouria explain we must picture the brain as a network.
“Think of it as a smooth surface or a quilt with a rolling ball on the surface, where the ball is our attention or cognition. On the quilt, there are these pockets where the ball can roll into,“ he illustrated. “These pockets are, essentially, brain regions or more local networks associated with specific functions.”
“This paper looks at different network properties (integration, segregation, and centrality) and how they look or change over the course of these five epochs,” explained Goicouria.
“The analogy here would be to say that how easily the ball travels between pockets (integration), how deep and distinct the pockets are (segregation), and which pockets are at key crossroads (centrality) look different and change differently during these five periods of our lives,” said Goicouria.
Brain development: Efficiency not the same as intelligence
While the study finds the adolescent brain to be far more efficient than the adult brain, few would argue that adolescents are thinking at a higher level than adults.
Goicouria, referring once more to his blanket analogy, explained, “global efficiency pertains more to how easily the ball travels between different pockets. But clarity of thought is more than just the ability to provide information between different local networks (pockets).”’
“As you get older,” he said, “wisdom and crystallized intelligence improve, which helps the world make more sense, but this is, partly, independent of your ability to make connections between different ideas.”
He noted that the paper explicitly points out that while “there is a positive association between global efficiency (more short paths for information transfer) and intelligence in children,” there is “a negative association between global efficiency and cognitive impairments in aging individuals.”
Does the teenage brain stage last until the 30s?
In recent years, other research has suggested that a defining characteristic of one’s adolescence is a significant overhaul of the prefrontal cortex, and a resulting diminishing of executive function until around age 25. This is not discussed in the study.
Goicouria wondered why this was not discussed, and asked:
“If executive function is supposed to improve during your twenties, why wouldn’t that have the kind of broad network effects that would define its own epoch? One could argue that it’s embodied in the transition between the second and third epochs (9–32, 32–66), but I imagine 32 is a little old for that.”
Study informs new strategies for neurosurgeons
Neurosurgeon Angela Bohnen, MD, FAANS, who likewise was not involved in this research, welcomed the study’s insights, saying: “In my experience performing complex brain surgeries across all age groups, this research provides scientific validation for what we observe clinically.”
“The brain’s capacity for surgical recovery changes dramatically throughout life,” Bohnen pointed out.
For a surgeon, these epochal differences matter.
For example, said Bohnen: “In infancy and in early childhood up to age 9, children have very high neuroplasticity — they have a multi-hub neural network. This allows them to recover quickly from some brain tumors after surgery.”
Bohnen said she has personally seen “optimal operations […] expected in surgery patients who, along with these complexities, display smoother convalescence by around age 32.”
At the same time, she noted, the study underscores the need for the development of new surgical techniques for patients over 66 years of age, who also need more recovery time, as do older people.
“Using information from this study into background developmental stages of people’s lives and their unique physical conditions,” said Bohnen, “researchers can design surgery that is suitable for an elderly man. This will help surgeons to make suitable decisions to restore function sooner based on the developmental stages of patients.”
The surgeon also noted that people over 83 are not typically considered candidates for neurosurgery.
