How the human brain transforms from birth to old age and beyond

The human brain undergoes remarkable changes from before birth to old age. Its development starts early, with rapid growth and complex shifts in function across a lifetime. Brain formation begins around 16 days after conception. During the second trimester, the fetal brain produces about 250,000 neurons every minute. At birth, it weighs 350 to 400 grams and already contains nearly all the neurons it will ever have.

By age six, the brain reaches roughly 90% of its adult size. Cognitive processing speed peaks between 16 and 25 years. Vocabulary and verbal reasoning continue to improve, often lasting until the late 60s or early 70s.

After 60, the brain loses about 0.5 to 1% of its volume each year. However, adults who stay physically, socially, and intellectually active experience slower cognitive decline. A strong cognitive reserve built over time can delay the onset of dementia symptoms by up to a decade.

By 85, around one in three people will have some form of dementia. Lifelong brain development and activity shape its resilience. While natural ageing brings changes, maintaining an active lifestyle can preserve cognitive function. This can postpone the effects of conditions like dementia well into later life.