Your Brain Can Still Change in Adulthood. Here Is What the Evidence Supports

Checked against primary sources by the Editorial Team. Every figure in this article was traced to the study it came from, including the ones that contradict what we previously published. How we review.

The old belief said the adult brain is finished by the mid twenties. The research since then points the other way: adult brains respond to what we do. But the strength of that evidence varies a lot from one claim to the next. Here is what the studies report, claim by claim.

Experience and brain structure: the London taxi study

Eleanor Maguire and colleagues scanned the brains of 16 licensed London taxi drivers and compared them with 50 control men who did not drive taxis. The authors report that the back part of the hippocampus was larger in the taxi drivers, while a front region was smaller. They also report that hippocampal volume tracked the time spent as a taxi driver. The right posterior hippocampus showed a correlation of 0.6 with years on the job.

The authors conclude that the healthy adult human brain has a capacity for local plastic change in response to environmental demands. One caution: this design compares groups at one point in time. It fits the idea that years of navigating changed the brain, but it cannot rule out that people with larger hippocampi were more likely to become taxi drivers. All participants were men, and the taxi group was small.

Do adults grow new neurons? Scientists disagree

The question of adult neurogenesis, the birth of new neurons, is contested. Maura Boldrini and colleagues examined postmortem tissue from 28 healthy people aged 14 to 79. They report similar numbers of immature neurons across those ages, along with less blood vessel growth and a smaller pool of resting progenitor cells in older people.

In the same year, Shawn Sorrells and colleagues reported the opposite. In their human tissue samples, new neuron production in the dentate gyrus fell sharply in childhood, and they could not detect it in adults. Both papers appeared in 2018, and the field has not settled the matter. So when you read that exercise or learning "grows new brain cells," treat it as an open question. We do not cite neurogenesis as the mechanism behind any finding below.

Learning demanding new skills: the Synapse Project

Denise Park and colleagues asked older adults to spend about 16.5 hours a week for three months on one of several activities. Some learned quilting, digital photography, or both. Others joined social activities without intellectual challenge, or did low demand mental tasks at home.

The authors report that episodic memory improved in the groups that took on demanding, new skills, compared with the groups doing receptive or social activities. They also report that social activity alone brought limited cognitive benefit. That finding runs against a common claim, including one in our earlier version, that conversation by itself trains the brain. The study supports sustained, effortful learning. The authors note that how those gains arise remains complex.

Training that transfers, and training that does not

The ACTIVE trial randomized 2,832 older adults across six U.S. cities to memory training, reasoning training, speed of processing training, or no training. Participants got ten sessions, with some receiving booster sessions later. Rebok and colleagues followed them for ten years. The authors report that the gains in reasoning and in speed of processing were still present at ten years, while the memory training gains were not. Participants in the trained groups also reported less difficulty with everyday activities such as managing meals and finances than the control group did.

Now compare that with commercial brain training. Daniel Simons and colleagues reviewed the evidence behind brain training programs. They report extensive evidence that people improve on the tasks they train, limited evidence of improvement on closely related tasks, and little evidence of improvement on distantly related tasks. None of the studies they reviewed met all of their best practice criteria. Practice makes you better at the practiced skill; that is well supported. Whether a game improves your daily thinking is not.

Exercise and the hippocampus

Kirk Erickson and colleagues ran a controlled trial with 120 older adults. They report that aerobic exercise training increased the size of the anterior hippocampus by about 2 percent, which they describe as reversing one to two years of age related volume loss, and that spatial memory improved. The control group lost volume. The authors also linked larger volume to higher blood levels of the protein BDNF.

Based on that finding, one way to act on it is regular aerobic exercise. This is one trial. The sources we read do not say how much exercise is needed, or whether the memory benefit holds in other groups. Our companion article on exercise and the brain weighs this trial against the larger reviews.

What this adds up to

The evidence supports a modest claim: adult brains are responsive to experience, and sustained, effortful learning is linked to better memory in older adults. It does not support promises that a specific app, supplement, or routine will rebuild your brain. Where a claim rests on one trial or one group, we have said so.