If you are interested, read [this](https://www.sciencedirect.com/science/article/pii/S2213158220301716) ([PDF](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7341447/pdf/main.pdf)) about Structural brain differences in pre-adolescents who persist in and recover from stuttering (2020). Persistency was associated with marginally smaller left frontal gray matter volume. Recovery was associated with higher mean diffusivity in white matter tracts. [Motor learning](https://www.google.com/search?q=Motor+learning+increase+gray+%22white+matter%22+%22motor%22+control) has been shown to lead to increases in both gray and white matter volume related to motor control and auditory processing.