As we age, the human mind reinvents itself.
The process occurs in distinct phases, or “epochs,” according to new research, as the structure of our neural networks changes and our brains reconfigure how we think and process information.
For the first time, scientists say they have identified four distinct turning points between those phases in the average brain: at ages 9, 32, 66 and 83. During each epoch between those years, our brains show very different characteristics in brain architecture, they say.
The findings, published Tuesday in the journal Nature Communications, suggest that human cognition does not simply increase with age until it peaks, then declines. In fact, the phase from 9 to 32 years is the only time in life when our neural networks are becoming more and more efficient, according to research.
During the adulthood phase, from 32 to 66, the brain architecture of the average person essentially stabilizes without major changes, at a time when researchers think that people are generally plateauing in intelligence and personality.
And in the years after the last turning point – 83 and beyond – the brain becomes increasingly dependent on individual regions as the connections between them begin to dry up.
“It’s not a linear progression,” said Alexa Mousley, a postdoctoral research associate at the University of Cambridge, who is the lead author of the study. “This is the first step in understanding the way brain changes vary with age.”
The findings may help identify why mental health and neurological conditions develop during particular phases of rewiring.
Rick Betzel, a professor of neuroscience at the University of Minnesota who was not involved in the research, said the findings are intriguing, but more data is needed to support the conclusions. Theories may not hold up to scrutiny over time, he said.
“They did this really ambitious thing,” Betzel said of the study. “Let’s see where she is in a few years.”
For their research, Mousley and her colleagues analyzed MRI diffusion scans – which are essentially images of how water molecules move within the brain – from around 3,800 people from age 0 to 90. The aim was to map the neural connections around the average person’s brain at different stages in life.
In the brain, the bundles of nerve fibers that transfer signals are encapsulated in a fatty tissue called myelin. Think of it like wiring or plumbing. The water molecules dispersed in the brain tend to move in the direction of these fibers, rather than around them, which means that the researchers can deduce where the neural pathways are located.
“We can’t break skulls open … we rely on non-invasive approaches,” Betzel said of this type of neuroscientific research. “What we’re trying to figure out is where these fiber bundles are.”
Based on MRI scans, the new study maps the neural network of an average person throughout life, and determines where connections are being strengthened or weakened. The five “epochs” she describes are based on the neural connections that researchers have observed.
The first phase is from 0 to 9 years, they suggest. The brain increases rapidly in gray and white matter; it prunes extra synapses and restructures itself.
From ages 9 to 32, there is an extended period of rewiring. The brain is defined by rapid communication throughout the brain and efficient connections between different regions.
Most mental health disorders are diagnosed during this time period, Mousely said: “Is there something about this second era of life, as we find it, that could lead people to be more vulnerable to the onset of mental health disorders?”
From 32 to 66, the brain plateaus. It is still rewiring itself, but less dramatically and more slowly.
Then, from 66 to 83 years, the brain tends towards “modularity”, where the neural network is divided into highly connected subnetworks with less central integration. At age 83, connectivity declines further.
Betzel said the theory described in the study is likely to resonate with people’s life experiences with aging and cognition.
“It’s intuitively something we gravitate towards. I have two kids and they’re really young. I think all the time, ‘I’m getting out of my toddler years,'” Betzel said. “Maybe the science will end up being there. But are those the exact right ages? I don’t know.”
In the ideal version of such a study, he added, researchers would have MRI diffusion data for a large group of people, each of whom was scanned during every year of life from birth to death. But this was not possible because the technology was not available decades ago.
Instead, the researchers combined nine different data sets containing neuroimaging from previous studies and tried to harmonize them.
Betzel said that each of those data sets varies in quality and approach, and the effort to make them correspond to each other can wash away important variability, which ultimately leads to a bias in the results.
However, he said the authors of the paper are “thoughtful” and skilled scientists who did their best to control for that possibility.
“Brain networks change throughout life – absolutely. Is it discrete such that there are five exact change points? I say stay tuned. It’s an interesting idea.”
This article was originally published on NBCNews.com