It’s no secret that our brains change as we age. The ease with which we form new connections—whether learning a language or picking up a new skill—shifts throughout life. But scientists are now showing just how dramatic and how patterned those shifts really are.
A new study from the University of Cambridge has identified five distinct phases of brain development across the human lifespan. The phases are marked by four turning points: ages nine, 32, 66, and 83, where brain rewiring shifts. “At different points in time, the brain is expected to be doing something different,” says Alexa Mousley, a research associate at the University of Cambridge and lead author of the study. “These phases show that the development of the brain is non-linear.”
To uncover these stages, researchers studied data from brain scans of nearly 4,000 people to identify where myelin—the fatty insulation that speeds electrical signals along nerve fibers—and the movement of water along those fibers, which helps reveal how different regions connect. “Myelin is basically insulating the connection, making it quicker,” Mousley explains.
By mapping these features from infancy through age 90, the team revealed how the brain’s communication pathways strengthen, stabilize, and eventually decline in recognizable patterns. These patterns may eventually help researchers identify why certain mental health issues develop at specific points in a lifetime and provide a benchmark for evaluating cognitive ability. Here’s what happens inside the brain at each stage.
Infancy to childhood (0-9): How the brain rewires itself
Early childhood is often seen as a period of rapid learning, but the research team found that the brain actually becomes less efficient during this period. Between birth and age nine, the number of synapses—the junction that allows neurons to pass signals—decreases as the child ages. Only the most active synapses survive, a pruning process that helps streamline the brain’s circuitry.