One of the most comprehensive studies conducted to date on changes in neural connections across the human lifespan identifies five significant “seasons” in the development of the human brain. The most striking conclusion is that adolescence may end after age 30!

The study suggests that human brain development has four critical “turning points”: at around ages 9, 32, 66, and 83.

These are four “changes of course” that define four seasons in brain development, the Guardian notes.

Scientists performed brain scans on nearly 4,000 individuals aged 1 to 90 and mapped their neural connections and how they evolve over a lifetime.

The childhood development period lasts from birth to about nine years old, when the brain transitions into the adolescent phase—a period that lasts until roughly age 32, on average.

From infancy to childhood, our brain is defined by “network consolidation,” as the number of synapses in an infant’s brain decreases and the most active ones survive.

Meanwhile, gray and white matter increase rapidly in volume, so that the cortex (the distance between the outer gray matter and the inner white matter) reaches its peak thickness, and the cortex’s folds—the characteristic ridges on the brain’s surface—stabilize.

In the second “season” of the brain, adolescence, white matter continues to increase in volume, making the organization of the brain’s communication networks increasingly sophisticated. This period is characterized by steadily increasing efficiency of connections throughout the brain, which is linked to enhanced cognitive performance.

“We’re certainly not saying that people under 30 will behave like teenagers, or even that their brain looks like a teenager’s brain,” said Alexa Mousley, the scientist who led the research. “We’re talking about the pattern of change.”

Around age 32, the strongest shift in development occurs, and neural connections transition to adult functioning—the longest phase, lasting more than three decades.

Major life events such as motherhood may play a role in some of the changes observed, although the study did not examine this specifically. “We know that in women who give birth, their brains change,” the researchers note.

From this age onward, the brain’s architecture appears to stabilize compared to earlier phases, corresponding to the final shaping of personality and intelligence.

A third turning point, around age 66, marks the start of a phase of “early aging” of the brain’s architecture. Finally, the “late-aged” brain forms around age 83.

The last two turning points are defined by a decrease in brain connectivity, believed to be related to aging and the degeneration of white matter.