It used to be thought that the supply of brain cells (neurons) one was born with were meant to last a lifetime and would never increase. Now it is known that brains can use stem cells to generate new neurons which helps with preserving memories, new learning, and trauma recovery. It is also known that the outer layer of the brain, the gray matter or cortex, becomes less able to change its structure in older age. This raises the question of how do older people learn new tasks?
In a study published in Nov. 2014 in Nature Communications a team of researchers led by Yuko Yotsumoto of the University of Tokyo and Li-Hung Chang of Brown University scanned the brains of two groups of people before and after they learned a new visual task. The younger group (age 19-32) showed changes in their visual cortex. In the older group (age 65-80) the people who learned the new task well showed changes in their white matter beneath the visual cortex and the ones who did poorly in learning the new task showed no changes. What this indicates is that in older people the brain re-organizes itself to make new learning possible by changing the structure of its white matter, not its gray matter.
How does this relate to traumatic brain injury? In TBI a blow to the head is more likely to cause bruising to the outer layer of the brain (the gray matter or cortex) while a whiplash injury (especially with head rotation) is more likely to shear or cut the white matter. This has implications for how older people are likely to respond after TBI depending on the mechanism of brain injury.