The wiring of our neurons evolves over the decades
Alexa Mousley, University of Cambridge
Our brain function is far from static throughout our lives. We already know that our ability to learn and our risk of cognitive decline vary from newborn to age 90. Scientists may have discovered a potential reason why this happens: Our brain wiring appears to undergo four major turning points at ages 9, 32, 66 and 83.
Previous research suggests that our bodies go through three rapid phases of aging around ages 40, 60, and 80. But the complexity of the brain makes it more difficult to understand.
The brain has distinct regions that exchange information via white matter pathways – threadlike structures made up of spindly projections, called axons, that project from neurons or brain cells. These connections influence our cognition, like our memory. But it was unclear whether major changes in this wiring occur throughout life. “No one has combined multiple measurements to characterize the phases of brain wiring,” says Alexa Mousley of the University of Cambridge.
To address this knowledge gap, Mousley and colleagues analyzed brain MRI scans of about 3,800 people in the United Kingdom and the United States, most of them white and ranging in age from newborns to 90 years old. These exams had already been carried out as part of various brain imaging projects, most of which excluded people with neurodegenerative or mental health problems.
Researchers have found that in people who reach age 90, brain wiring has typically undergone five main phases, separated by four key turning points.
In the first phase, which occurs between birth and age 9, the white matter pathways between brain regions appear to become longer or more convoluted, making them less efficient. “It takes longer for information to flow between regions,” says Mousley.
This could be because our brains are full of many connections when we are infants, but as we grow and experience things, the ones we don’t use are gradually removed. The brain seems to prioritize making a wide range of useful connections for things like learning to play the piano, at the cost of their efficiency, Mousley says.
But during the second phase, between ages 9 and 32, this pattern seems to reverse, which is potentially due to the onset of puberty and its hormonal changes that influence brain development, says Mousley. “Suddenly, the brain increases the efficiency of connections: they become shorter, so that information moves more quickly from one place to another. » This can support the development of skills such as planning and decision-making, as well as improving cognitive performance, such as working memory, says Mousley.
The next phase is the longest, ranging from 32 years to 66 years. “This phase is a time in your life where your brain, of course, continues to change, but much less,” says Mousley. Specifically, connections between brain regions gradually lose effectiveness, she says. “It’s not clear what’s driving this change, but the 1930s correspond to many major changes in lifestyle – for example, having children, settling down – so that could play a role,” says Mousley. It could also just be due to general wear and tear on the body, says Katya Rubia of King’s College London.
From 66 to 83 years old, researchers discovered that connections between neurons in the same brain region appear more stable than between those in distinct areas. “It’s interesting because around this time there is an increasing risk of developing diseases such as dementia and general health problems,” says Mousley.
In the final phase, between ages 83 and 90, the connections between brain regions weaken and increasingly pass through “hubs” that connect many areas. “This suggests that there are fewer resources to maintain connections during this phase, so the brain relies more on using certain regions to act as hubs for connections,” says Mousley.
Understanding these brain changes could help explain why mental health problems typically occur before age 25 and why people over 65 are at particular risk of dementia, she says.
“It is important to understand the normal turning points in brain structure over the human lifespan, so that we can, in future studies, explore what deviates in cases of mental health or neurodegenerative diseases,” says Rubia. “Once you understand what is deviating, it can help you identify ways to treat it. For example, you can explore what environmental factors or chemicals are causing these differences and find ways to reverse them using therapy, policies or medications.”
But first, more studies are needed to determine whether the findings apply to more ethnically and geographically diverse populations, Rubia says.
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