Maturity is a socially useful notion. It plays a role in a number of different domains, including law, policy, and medicine. The age of majority in the US is set at 18, but there are some decisions for which adolescents are deemed mature enough to make earlier, for instance the age of consent at 16, or later, like the right to consume alcoholic beverages at 21. Although there are practical justifications for designating a specific time as the moment one becomes an adult, there is little reason to think that turning 18 corresponds with a particular physical process of maturation.
In a recently published article in Neuron, Leah H. Somerville, tackles brain development and reveals the complexities involved in identifying a physical anchor for the notion of maturity. Somerville explains that maturation in the brain can trail a number of different processes, including structural changes and shifts in connectivity. Structural changes characterized by the reduction of cortical gray matter continue throughout one’s 20s and 30s, but there are studies that indicate that this process does not plateau and continues into old age--challenging the notion that there is a point at which the brain becomes structurally mature. Adolescence is also a time of increased widespread connectivity, a process that slows down in one’s early 20s. But there is a great deal of individual variation, with some children having higher connectivity than some young adults, which makes it difficult to use these data about populations to identify a point of maturity for an individual. Furthermore, since structural changes in the brain and shifts in brain connectivity do not happen at the same time, as Somerville points out, maturity based on network connectivity can occur decades sooner than based on structural changes.
A way of circumventing the difficulty in identifying a physical marker for a general notion of maturity is to adopt a context specific version of the concept, where we don't ask whether an individual is mature but whether they are mature in a particular way. This would allow us to define maturity in terms of the cognitive skills required to make decisions within a certain realm. We have done this in medicine when we ask whether a patient has the cognitive capacity to make a specific decision and we measure their ability to do so in relation to the particulars of the medical situation. In some instances an individual could have the ability to make one decision, such as select a surrogate decision maker, but lack capacity to make another, such as consent for a complex surgical procedure. Although children are presumed to lack capacity, adolescents are in some states allowed to accept or refuse treatment depending on their ability to understand and appreciate the risks and benefits of treatment. Moreover, even in adulthood, age is not an indicator of capacity to make medical decisions and any individual could, for a number of different reasons, lose the ability to make medical decisions. We could treat maturity similarly as a task-specific ability that over time generalizes to more and more situations.
I would think that behavioral tests of maturity are likely to be more accurate than tests of brain structure and connectivity, at least for a while. Much of what we are trying to determine from tests of brain structure and connectivity is what they can tell us about behavior. So it's less roundabout to focus directly on behavior.
Eventually, though, it might be easier to fool a behavioral test of maturity than a brain-based test. Also, I suppose there may be some issues that are hard to assess behaviorally: for example, not whether a person would engage in some behavior but what thought processes are likely to accompany it.
I couldn't agree more about your general point about sharp age cut-offs:
https://papers.ssrn.com/sol3/papers.cfm?abstract_id=1992034
Thanks, Nada!
Posted by: Adam Kolber | 01/10/2017 at 07:03 AM