In a new study, researchers discovered that the human brain has four pivotal periods when it goes through marked changes, sparking five “epochs” that last for years. The adolescent phase, for example, was found to extend into our early 30s.
To carry out the study, researchers at the University of Cambridge looked at data from 3,802 people ranging from newborns to 90 years old who had undergone MRI diffusion scans. These scans track the movement of water molecules through brain tissue, which helps scientists map the pathways of neural connections.
The study found that there are four times in our lives when the brain undergoes significant topological changes before stabilizing for a period of years. Each of these times kicks off another phase in the structure and organization of our brains, which can impact our thinking and potentially help scientists going forward better understand brain development and conditions that might impact it.
“We know the brain’s wiring is crucial to our development, but we lack a big picture of how it changes across our lives and why,” said Dr. Alexa Mousley, a Gates Cambridge Scholar who led the research. “These eras provide important context for what our brains might be best at, or more vulnerable to, at different stages of our lives. It could help us understand why some brains develop differently at key points in life, whether it be learning difficulties in childhood, or dementia in our later years.”
The first phase was found to run from birth to around age nine. This phase is marked by what’s known as “network consolidation,” during which the huge array of synapses we are born with are slowly reduced, making space for the most active ones to survive. It’s also a period of time during which gray and white matter grow quickly, leading to a peak of our cortical thickness – the brain’s outer layer which thins with age and neurological conditions like Alzheimer’s disease.
After approximately age nine, the brain enters its adolescent phase. During this phase, the brain works to make neural connections shorter, and therefore more efficient – both in specific regions and across the entire brain. Surprisingly, the adolescent phase lasts until about age 32.
Phase shift
After that point, the brain moves into the adult phase and that shift marks the strongest turning point in the brain’s evolution, say the researchers.
“Around the age of 32, we see the most directional changes in wiring and the largest overall shift in trajectory, compared to all the other turning points,” said Mousley.
The adult phase marks the longest epoch of brain evolution. During this time, the brain remains relatively stable with not much change happening for about 30 years. There is, however, a gradual shift toward a segregating process in which brain regions become more compartmentalized.
The next shift in brain evolution comes around age 66 and once again is nowhere near as dramatic as the changes that solidify in our early 30s. In this phase, the brain still works to reorganize itself, although that process slows and cortical thickness begins to lessen.
“The data suggest that a gradual reorganization of brain networks culminates in the mid-sixties,” said Mousley. “This is probably related to aging, with further reduced connectivity as white matter starts to degenerate. This is an age when people face increased risk for a variety of health conditions that can affect the brain, such as hypertension.”
The final phase of brain evolution kicks in around age 83. While the researchers say data for this period of time was hard to come by, they did find out that the brain begins to shift its processing from a global model to a more localized one, leading people to rely on specific regions for cognition rather than processing across the entire organ.
“Many neurodevelopmental, mental health and neurological conditions are linked to the way the brain is wired,” concluded senior study author Duncan Astle. “Indeed, differences in brain wiring predict difficulties with attention, language, memory, and a whole host of different behaviors. Understanding that the brain’s structural journey is not a question of steady progression, but rather one of a few major turning points, will help us identify when and how its wiring is vulnerable to disruption.”
The study has been published in the journal Nature Communications.
Source: University of Cambridge