Do Adult Brains Grow New Neurons? Scientists Disagree
How brains can still change at any age — and where the science is genuinely unsettled
"You can't teach an old brain new tricks" is false as a general claim — but exactly how adult brains change is more contested than popular brain-training content usually admits.
What's Well Established: Structural Plasticity Continues
The juggling study covered in Section 1 is one of many demonstrating that learning a genuinely new, demanding skill produces measurable structural change in adult brains — not just in children or young adults[1]. This kind of experience-dependent structural plasticity — strengthening of existing connections, changes in grey matter density in task-relevant regions — is well replicated across many different skills and age groups. This part of the neuroplasticity story is solid.
What's Genuinely Contested: Adult Neurogenesis
A separate and more specific question — whether the adult human brain generates meaningful numbers of entirely new neurons in the hippocampus throughout life (adult neurogenesis) — is currently unresolved in the scientific literature, and it's worth being direct about that rather than picking a side. One rigorous study using multiple tissue-analysis methods concluded that hippocampal neurogenesis in humans drops to undetectable levels by adulthood[12]. A separate, similarly rigorous study using different methodology and different tissue-selection criteria concluded the opposite — that meaningful neurogenesis persists throughout aging[13]. The most likely explanation for the contradiction involves real methodological differences between the studies, including tissue-preservation techniques and the health status of the donor tissue used, rather than either study being straightforwardly wrong. This is genuinely unsettled science, not a case where one popular claim is simply correct and its opposite is fringe.
Why the Disagreement Doesn't Undermine the Practical Advice
The practical recommendations in this guide — exercise, sleep, novel skill-learning, stress management — don't depend on resolving the adult-neurogenesis question. The structural-plasticity evidence (existing connections strengthening, grey matter changes in task-relevant regions) is solid regardless of whether new neurons are also being generated, and the exercise-BDNF evidence in Section 6 stands on its own randomised-trial data. Whether or not literally new neurons are involved, the overall picture — that adult brains remain meaningfully responsive to exercise, learning, and experience — holds up.
Section takeaway
Adult brains genuinely continue to change structurally in response to learning and exercise — that part is solid. Whether this specifically involves generating new neurons in the hippocampus is an open scientific question, not a settled fact in either direction, and treating it as more certain than it is would be dishonest.