The claim "This is the first long-range study, using a type of imaging that looks at brain wiring, to show that in the white matter there are still structural changes happening during young adulthood," by Lebel is quite surprising given the article published on 1993:

Ann Neurol. 1993 Jul;34(1):71-5.
When does human brain development end? Evidence of corpus callosum growth up to adulthood.
Pujol J1, Vendrell P, Junqué C, Martí-Vilalta JL, Capdevila A.
Author information
Abstract
To locate structural changes in the brain accounting for the increasing effectiveness in cognition and skills that occurs at the final stage of behavioral development, we attempted to determine the age at which the corpus callosum completes its active growth period. We assessed the growth rate of the corpus callosum by measuring its area twice on midsagittal magnetic resonance imaging scans separated by a 2-year interval, in a series of 90 subjects with a wide range of ages. We observed an increase in the size of the corpus callosum as long as human mentation expands, up to the middle 20s. Clinical and experimental data about the corpus callosum, together with the present findings, suggest that the corpus callosum is part of the highest order-latest maturing neural network of the brain.
PMID: 8517683 [PubMed - indexed for MEDLINE]