19) Myelination

Interestingly, the myelination occurs last in the prefrontal cortex and finalizes sometime in the late twenties and early thirties and turns from gray to white. These transformations have profound impact on the assertive and attentive behaviors described in this book because the prefrontal cortex, or orbitofrontal cortex, begins to manifest these qualities:
        Impulse inhibition
        Goal setting
        Initiating appropriate behavior
        Modifying behavior to accommodate situations

Children often respond to their world in an impulsive manner without considering the ramifications of their behavior. Their emotional midbrain section undergoes the myelination before the prefrontal cortex, which accounts for why children through adolescence will respond to situations impetuously rather than with some reflection.

Bartzokis G., Beckson M., Lu P., Nuechterlein K., Edwards N., Mintz J., (May 2001). Age-related changes in frontal and temporal lobe volumes in men: a magnetic resonance imaging study. Arch Gen Psychiatry. 58(5):461-5.

Gudrais, E., (2001). Modern Myelination: The Brain at Midlife, Harvard Magazine, 103: 5, 9.