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Brain Development: 10 Ways Your Brain Changes as You Get Older

Your brain development doesn't stop after you're a baby. It continues to grow new brain cells and connections—but decline starts earlier than you'd think.

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In uterus: Brain cell growth

Before you took your first breath, your body was busy with brain development, preparing for life outside the womb. Newborns have about 100 billion neurons, says David Perlmutter, MD, neurologist and #1 New York Times bestselling author of Brain Maker: The Power of Gut Microbes to Heal and Protect Your Brain for Life. “That means the average rate of growth of brain cells during pregnancy is about 250,000 new brain cells per minute,” he says. Here are 50 more incredible things you didn’t know about the human brain.

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Newborn: More neurons and connections are built

At birth, your brain is about 60 percent of the size it will be when you’re full-grown, says Frances Jensen, MD, member of the American Neurological Association board of directors, chair of the University of Pennsylvania neurology department, and author of The Teenage Brain: A Neuroscientist’s Survival Guide to Raising Adolescents and Young Adults. Your brain starts at about 20 cubic inches, then grows another 14 cubic inches in the first 90 days after birth, says Dr. Perlmutter. “It comes close to doubling within the first three months,” he says. At birth, the only myelin—a fatty substance that insulates your brain’s axons to help signals move faster—is near the spinal cord. That area of the brain is in charge of basic functions like breathing, eating, and controlling heart rate, says Dr. Jensen.


Toddler: Brain builds up and cuts the fluff

By the time you’re three years old, your brain is about 80 percent of its adult size in terms of volume and brain cells, says Dr. Perlmutter. “The brain of a three-year-old is extremely sophisticated and might be more [sophisticated] than any other animal on the planet,” he says. At that age, the brain actually has 200 percent more synapses as an adult’s. As brain development continues, your mind starts “pruning” by breaking down those synapses. Getting rid of the connections it doesn’t use lets the brain focus its energy on the connections that matter.


Early childhood: Experiences shape the brain

The years leading up to a child’s fifth birthday are part of the “critical period” of development, says Dr. Jensen. At this point, experiences are directly shaping the way synapses form. “Everyone’s brain is being customized for their environment,” says Dr. Jensen. On one hand, this means negative experiences can leave a psychological scar on the child forever. But on the flip side, it also means early intervention programs and efforts to reverse the effects of traumatic experiences are more effective than ever. (Look for these 11 signs your child is a genius.)

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Adolescence: Decision-making still isn’t strong

Teen brains look adult-like in terms of weight, but they aren’t fully developed yet. Your body has been producing myelin from the back of the brain (which is in charge of the most basic functions) to the front (which has more complex circuits). The last area to be fully myelinated is the frontal lobe, which is important for decision-making, impulse control, and empathy, says Dr. Jensen. While an adult’s frontal lobe knows when to say “no” to peer pressure and risks, adolescents haven’t developed that skill yet. “It’s like a Ferrari with weak brakes,” says Dr. Jensen. Mom and Dad may be tearing their hair out at a teen’s bad decisions, she explains, but parents should to practice patience and provide guidance: Teens need “frontal lobe assists” to avoid poor choices.


20s: Switch from brain development to decline

By the time you’re in your mid to late 20s, the brain development of your frontal lobe has finally finished myelination—especially in the frontal lobes you need for judgment. You’ll continue forming and eliminating synapses and brain cells your whole life, but there is one potential drawback to the development of your frontal lobe: Now, mental illnesses like schizophrenia or anxiety can flare up. About 60 to 80 percent of people with major affective disorders are diagnosed between 18 and 25, says Dr. Jensen. “The frontal lobe needs to be connected up to a point to be able to manifest these diseases,” she says. (Start these 36 everyday habits that reduce your risk of Alzheimer’s as early as you can.)


30s and 40s: Learning gets harder

In your 20s, your brain slows down production of brain cells and synapses—plus it’s not doing as much “pruning”—which is why you have a harder time learning by the time you reach your 30s. Meanwhile, your diet and exercise habits are setting you up for a strong—or forgetful—mind in the decades ahead. These are the worst foods for your brain that you should avoid in every stage of life.

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50s: Memory starts to slip

Most people start noticing their mind slipping in their 50s, starting with short-term memory. “We call these ‘senior moments’ and write it off and make jokes,” says Dr. Perlmutter. Still, about 5 percent of Alzheimer’s diagnoses are early-onset, so don’t ignore symptoms that could be a sign of serious memory loss. Find out which fixable problems could be behind your memory loss.

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60s and 70s: Connections are lost faster than they’re made

One in ten adults age 65 and up have Alzheimer’s disease. Between genetics and lifestyle risks, the risk doubles every five years after age 65. The causes of the condition aren’t entirely clear, but scientists do know as we age, our brain cells and synapses decline. “These connections are dropping away, so the signals don’t get from here to there,” says Dr. Perlmutter. “You look at an object and suddenly can’t name it anymore because you can’t connect to the part of the brain where the name was stored.” Don’t miss these 12 signs your brain is aging faster than you are.

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80s and up: Alzheimer’s risk skyrockets

By the time you reach 85, you have almost a 50 percent risk of Alzheimer’s. That doesn’t mean the fate of your memory is sealed, though. While genetics play a factor, challenging your mind with brain-boosting activities and socializing can help. One method stands above the rest: “By far the most powerful thing is aerobic exercise,” says Dr. Perlmutter. In a ten-year study of more than 3,700 adults aged 60 and up, those who exercised the most had the largest brains and lowest risk of dementia compared to those who got the least physical activity. The protective effect was strongest for those 75 and older. Aim for 20 minutes of aerobics every single day, recommends Dr. Perlmutter. Check out these healthy brain habits your 80-year-old self will thank you for.