Transforming Tracts

Our brains don’t stop developing in our teenage years – they keep changing well into our 20s, a new study shows.

White matter, switchin' it up (that's the actual scientific term).

By imaging the “wiring” of different brain areas, researchers have determined that white matterconnective brain material consisting mainly of the axons (branches) of neurons – continues to grow and change throughout our 20s. This means the connections between different areas of your brain may be transforming even as you read this article.

The idea that our brains’ functional connectivity patterns change as we age isn’t new – in fact, I’ve written about it here before. But this new data shows that even structural connectivity doesn’t stop changing when we grow out of adolescence.

As the Journal of Neuroscience reports, a team led by the University of Alberta’s Christian Beaulieu and UCLA’s Catherine Lebel figured this out by performing diffusion MRI scans on the brains of 103 volunteers between the ages of five and 32. They then compared this set of scans with a second set taken from the same volunteers a while later, and found that many of the subjects’ white matter was continuing to change its structure:

All tracts showed significant nonlinear development trajectories for FA and MD [two scanning parameters]. Significant within-subject changes occurred in the vast majority of children and early adolescents, and these changes were mostly complete by late adolescence for projection and commissural tracts. However, association tracts demonstrated postadolescent within-subject maturation of both FA and MD.

In other words, white matter tracts that carry information between separate brain areas, and out of the brain into muscles, or into the brain from sense receptors (projection tracts) and ones that carry information between the left and right hemispheres (commissural tracts) both generally stop growing by late adolescence – but tracts that carry information between different lobes of the same hemisphere (association tracts) continue to develop into our late 20s. Growth was particularly focused in the frontal lobe – an area involved in complex thought and decision-making.

It’s interesting to note, though, that some volunteers’ white matter tracts showed degradation over time. Because many psychiatric disorders first manifest themselves in adolescence, the researchers suspect these problems may be linked to connections between brain regions that degrade prematurely:

What’s interesting is 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.

If that turns out to be true, scans like these could soon be used to predict psychiatric diseases, or even chart their progress. By comparing the diffusion MRI scans of psychologically healthy patients against those of patients suffering from, say, depression or anorexia, doctors might be able to get a clearer sense of what’s going on in these patients’ heads – on both the physical and psychological levels.

So next time you’re reflecting on how much you’ve changed over the past few years, stop for a second and you literally have a different brain than you did then. And then maybe you could run into the street screaming, “Who am I?!” Try to remember to put pants on first.

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