Myelin and Neuroscience, the short story
Well, 800+ pages of Neuroscience textbook later, (1), the short story on myelin regeneration is - while regrowth is somewhat possible to damaged areas outside of the brain, it doesn't really happen much within the brain. Preventing breakdown and maintaining or adding to the synaptic connections that exist may be a more realistic goal. The chemical signals that occur from inflammatory white blood cells can lead to increased breakdown of cells and myelin, and may also cause increased production of unnecessary protein or cells, somewhat like building scar tissue to wall off a damaged area - but if inflammation is occurring throughout the brain than large areas of the brain are developing the scar tissue.
In addition to stopping the causes of inflammation and providing the body with adequate nutrients and antioxidants to cope with oxidative stress, the "use it or lose it" principle sometimes mentioned in exercise may apply to the brain and synaptic connections. Staying mentally and socially active as well as physically active is helpful for maintaining the synaptic connections and nerve connections that connect brain cells with each other and with the muscles and rest of the body parts. If synaptic connections aren't used they may be more likely to be lost, dismantled for spare parts possibly if there is some nutrient deficiency.
The nerve connections between cells can be as long as an arm or a leg for some that connect the spinal cord with muscles in the hand or foot and the synaptic connection is right the very end. The route between is like a little tunnel where protein and signalling chemicals are transported from the cell body in the spine all the way to the synaptic junction near a nerve cell in the hand or foot. Energy producing mitochondria also travel along this route from the cell body out to the synapse. Aging seems to cause a breakdown in the internal transport system within the tunnel and then the synapse is less likely to be able to receive the mitochondria or other signaling proteins that are produced within the cell body. The body is a miracle but it needs help from adequate protein, essential fats, and adequate carbohydrate in addition to all the more specialized vitamins and minerals.
I have more reading to do, review the introductory textbook and read more of the advanced topics in more specific research articles. The good news though remains - prevention of inflammation is possible with diet and lifestyle changes, (see the summary points in the last post), however the clean air, water, and avoidance of other environmental toxins might be more difficult depending on where you live.
Addition: Spinal cord injuries may have more potential for healing than brain injuries - brain cells that are involved with smelling are some of the few types of brain cells that continue to divide and replicate throughout life, possibly because they are more exposed to the outside world. Transplanting some of them into the area of a spinal injury has had some success for reversing paralyzing damage to the spine. (2)
Disclosure: This information is provided for educational purposes within the guidelines of fair use. While I am a Registered Dietitian this information is not intended to provide individual health guidance. Please see a health professional for individual health care purposes./
Neuroscience, 6th Edition, Editors D. Purves, G.J. Augustine, D. Fitzpatrick, W.C. Hall, A.S. LaMantia, R.D. Mooney, ML. Platt, L.E. White, (Sinauer Associates, Oxford University Press, 2018, New York) (Barnes&Noble)
Anna Z, Katarzyna J-W, Joanna C, Barczewska M, Joanna W, Wojciech M. Therapeutic Potential of Olfactory Ensheathing Cells and Mesenchymal Stem Cells in Spinal Cord Injuries. Stem Cells International. 2017;2017:3978595. doi:10.1155/2017/3978595. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5337375/