For many years, the convention was that after adolescence, the brain had done about as much developing as it was going to do. Recent research has changed that notion, however, with studies finding that the brain can actually grow new neurons in certain areas. Now, a group reports that the fiber tracks connecting brain cell to brain cell (the white matter of the brain) may also continue to develop into early adulthood.

Association tracts, which connect different regions within one side of the brain, continued to proliferate into early adulthood for up to half of the participants.

The team of researchers scanned participants’ brains using magnetic resonance imaging, MRI, at two time points or more. At the beginning of the study, the participants ranged in age from 5 to 29, and the average gap between the first and second scanning was about four years. They focused on 10 white matter tracts in the frontal lobes of the participants’ brains, monitoring how they changed over the study period.

They found that for two types of connections – projection tracts, which connect the cortex to other parts of the brain and spinal cord, and commissural tracts, which connect the two hemispheres of the brain – did not change after adolescence. But association tracts, which connect different regions within one side of the brain, continued to proliferate into early adulthood for up to half of the participants.

Figure 1.
Connections between brain cells proliferate between two time points.

Courtesy of The Journal of Neuroscience.
Click image for larger view.

The frontal lobe, studied here, is responsible for high-level executive function and attention. The authors suggest that this frontal lobe “postadolescent development may be influenced by complex and demanding life experiences such as advanced education, full-time employment, independence, and new social/family relationships.” Since the structure of the brain can change in response to learning experiences, they say, it’s feasible that “life lessons” could shift connections in similar ways.

Another notable finding was that in a minority of people, the white matter tracts actually diminished with time, which could be linked to brain degeneration or psychiatric problems. The white matter in the frontal lobe is known to be underdeveloped in people with mood disorders, anxiety, and schizophrenia, which often develops by young adulthood.

Study author Christian Beaulieu says that “a lot of psychiatric illness and other disorders emerge during adolescence, so some of the thought might be if certain tracts start to degenerate too soon, it may not be responsible for these disorders, but it may be one of the factors that makes someone more susceptible to developing these disorders.”

More work is needed to follow up on the idea that brain changes could be markers of problems to come. But the fact that our brains continue to mature into early adulthood shows once again that the brain is more plastic than previously thought, which researchers are just beginning to illustrate in detail.

The study was carried out at the University of Alberta, and published in the July 27, 2011 issue of the Journal of Neuroscience.