A team of neuroscientists at the University of Cambridge in the United Kingdom identified five broad phases of brain structure over the course of an average human life. These eras occur as the human brain rewires to support the different ways of thinking while we grow, mature, and eventually decline. The five major turning points are detailed in a study published today in the journal Nature Communications.
In the study, they compared the brains of 3,802 people between ages zero and 90, using datasets of MRI diffusion scans. These types of MRIs map neural connections by following how water molecules move through brain tissue. They detected five broad phases of brain structure in the average human life that are split up by four pivotal turning points between birth and death when our brains reconfigure.
The major turning points occur at ages:
- Nine (Childhood brain architecture)
- 32 (Adulthood brain architecture)
- 66 (Early aging)
- 83 (Late aging)
“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,” study co-author and neuroscientist Dr. Alexa Mousley said in a statement. “This study is the first to identify major phases of brain wiring across a human lifespan. 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.”
Age nine–From baby to kid
From infancy through early childhood, the brain is defined by network consolidation. All of the connectors between neurons called synapses that were overproduced in a baby’s brain whittle down. The more active synapses survive, shaping the brain’s early architecture.
Across the whole brain, these connections rewire in the same pattern from birth until about nine years old. Meanwhile, the brain’s grey and white matter grow rapidly in volume.
The childhood brain runs from birth up until a turning point at the age of nine. Here, the brain is experiencing a change in cognitive capacity, but also an increased risk of mental health disorders.
Age 32–Adult brain takes shape
In the early 30s, the brain’s neural wiring shifts into adult mode. White matter continues to grow in volume, so the brain’s communications networks are increasingly refined based on MRI scans showing how water molecules movies. These changes keep the brain at an enhanced level of cognitive performance that peak in the early 30s and is the brain’s “strongest topological turning point” of the entire lifespan, according to the team.
“Around the age of 32, we see the most directional changes in wiring and largest overall shift in trajectory, compared to all the other turning points,” said Mousley. “While puberty offers a clear start, the end of adolescence is much harder to pin down scientifically. Based purely on neural architecture, we found that adolescent-like changes in brain structure end around the early thirties.”
Adulthood is the longest era and three decades. The brain’s architecture also stabilizes compared to previous phases, without any major turning points for the next 30 years. According to the team, this corresponds with a “plateau in intelligence and personality.”
Dr. Alexa Mousley, University of Cambridge
Age 66–Early aging begins
This mid-60s turning point marks the start of an “early aging” phase of brain architecture. It’s a more mild period and is not defined by any major structural shifts. However, the team still uncovered meaningful changes to the pattern of brain networks on average at around age 66.
“The data suggest that a gradual reorganisation 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.”
Age 83–Late aging
The last turning point comes around age 83. The data for this final era is more limited, but the defining feature is a shift from global to local. Whole brain connectivity declines even further and it relies on certain regions as others fade.
“Looking back, many of us feel our lives have been characterised by different phases. It turns out that brains also go through these eras,” added study co-author and neuroscientist Duncan Astle. “Many neurodevelopmental, mental health, and neurological conditions are linked to the way the brain is wired. Indeed, differences in brain wiring predict difficulties with attention, language, memory, and a whole host of different behaviours”
Understanding that our brain’s structure journey is generally one of a few major turning points instead of a steady progression can help neuroscientists better identify when and how the wiring is more vulnerable.
