The wiring of our neurons changes over the decades
Alexa Moseley, University of Cambridge
Our brain The function is far from static throughout our lives. We already know that our learning ability and risk of cognitive decline varies from newborn to age 90. Now scientists may have discovered a potential reason why this happens: Our brain structure appears to undergo four major turning points at ages 9, 32, 66 and 83.
Previous research shows that our body goes through three rapid bursts of aging at approximately 40, 60 and 80 years of age. But the complexity of the brain makes it difficult to understand.
The brain has distinct regions that communicate through white matter tracts, wire-like structures made up of spindle-shaped projections called axons that extend from neurons, or brain cells. These connections influence our cognition, such as our memory. But it was unknown whether major changes in this pattern occur across the lifespan. “No one has combined several measures together to characterize phases of brain function,” says Alexa Moseley at Cambridge University.
To fill this knowledge gap, Moseley and her colleagues analyzed MRI brain scans of about 3,800 people in the UK and US who were mostly white and aged from newborns to 90 years. These images were previously carried out as part of various brain imaging projects, most of which excluded people with neurodegenerative or mental health conditions.
Researchers have found that in people reaching age 90, brain structure typically undergoes five major stages, separated by four key turning points.
During the first stage, which occurs between birth and age 9, white matter pathways between brain regions become longer or more tortuous, making them less efficient. “It takes longer to transfer information between regions,” Moseley says.
This may be because as babies our brains are filled with many connections, but as we grow and experience, the ones we don't use are gradually cut off. The brain appears to prioritize making a wide range of connections that are useful for things like learning to play the piano, but this makes them less efficient, Moseley says.
But in the second stage, between ages 9 and 32, this pattern appears to change, potentially due to the onset of puberty and its hormonal changes affecting brain development, Moseley says. “Suddenly the brain makes connections more efficient—they become shorter, so information gets from one place to another faster.” This can help develop skills such as planning and decision making, as well as improvement of cognitive functions“such as working memory,” Moseley says.
The next phase is the longest, spanning from 32 to 66 years. “This phase is a point in your life when your brain is still changing, of course, but much less,” Moseley says. In particular, she says, connections between brain regions are slowly starting to lose effectiveness again. “It's not clear what exactly is driving this shift, but the 30s are associated with a lot of different major lifestyle changes—like having kids, settling down—so that could play a role,” Moseley says. It may also be due to general wear and tear on the body, he says. Katya Rubia at King's College London.
The researchers found that between ages 66 and 83, connections between neurons in the same brain region appeared more stable than connections between neurons in different regions. “It's interesting because around this time the risk of developing diseases such as dementia and general health problems increases,” Moseley says.
In the final stage, from 83 to 90 years of age, connections between brain regions weaken and increasingly pass through “nodes” connecting multiple regions. “This suggests that at this stage there are fewer resources available to maintain connections, so the brain relies more on using certain areas as connection centers,” Moseley says.
Understanding such changes in the brain may help explain why mental disorders usually occurs before age 25 and why are people over 65 years old particularly at risk of dementiashe says.
“It is important to understand normal turning points in brain structure across a person's lifespan so that in future studies we can examine what abnormalities occur in mental health or neurodegenerative conditions,” says Rubia. “Once you understand what's deviating, it can help you identify treatments. For example, you can study what environmental factors or chemicals are causing the differences and find ways to reverse them through therapies, policies or drugs.”
But first, further research is needed to see whether the findings apply to more ethnically and geographically diverse populations, Rubia says.
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