Q. Is my 22-year-old son at risk for making poor decisions until his brain is completely myelinated?

A. Myelination is only one factor to consider (e.g., maturation of the pre-frontal cortex is another), but since that was your question I’ll confine my remarks to that topic. Myelination is a term that describes the process the nervous system goes through to put insulation around nerve fibers. It is analogous to using insulated wire in a building (e.g., to enhance safety, prevent shorting out, avoid fires, prevent electrical leakage).

Myelin is a cholesterol sheath that coats neuronal axons acting as a form of insulation. Specific skills can be perfected only when appropriate myelinization of the nerve pathways or enervation of the muscle tissue is incomplete (e.g., expecting conscious control of the anal sphincter and bowel movements in a child who is only 14 months old is unrealistic).

• Myelination of the reticular formation (brain tissue that helps you to maintain attention) is probably completed around puberty or sometime soon thereafter.
• Myelination of the corpus callosum occurs at a highly predictable rate from back to front, spanning birth to approximately 21 years of age, or longer.
• Myelination of the frontal lobes begins about the time verbal language develops but the process can take years to complete, until the early twenties.

Until key portions of the brain are myelinated, the individual may not have complete access to key functions (e.g., reflective analysis, decision-making). Thus, the individual with a partially myelinated brain is more likely to exhibit behaviors from time to time that might be viewed by others as indicative of “shorting out.”

Every human being is a risk for making poor decisions at one time or another. And it stands to reason that the younger the person’s brain, the greater the risk in some areas. Having said that, some 22-year-olds make less than optimum decisions, as you put it, because they have had relatively little experience in making decisions. They have pretty much been expected to do what they were told to do by others. Making optimum decisions requires personal experience.