June 21, 2018

The Teenage Brain: What Are They Thinking?

How many times a day do parents of teenagers find themselves asking the teen, "What on earth were you thinking?" The answer is, they were thinking, just with the wrong part of their brain.

Adolescence is the period of growth, development, and exploration. Teenagers are near the peak of physical health, strength, and mental capacity, and yet, for some, this can be a hazardous age. The top causes of death in teenagers are accidents, homicide, and suicide. Other causes of morbidity, including unintended pregnancy, sexually transmitted infections, and substance use, are related to risk taking behaviors and are largely preventable.

The teenage brain is still developing; in fact, it keeps developing until the mid-20s! Let's look at this in more detail, following the same trajectory of brain development: back to front.

The lowest part of the brain, the hind brain, controls basic survival functions and is composed of the medulla, pons, and cerebellum. The medulla coordinates heart rate, blood pressure, and breathing. The pons deals primarily with sleep, swallowing, hearing, equilibrium, and facial expressions. Cerebellum coordinates movement, including coordination and precision of movement. Much of the hind brain is fully developed at birth, however some, like the cerebellum, continue to develop during childhood.

As we move towards the front of the brain, we come to the occipital lobe, or the visual processing center. The temporal lobe is in front of the occipital lobe as is the part that controls more advanced skills including language comprehension, processing sensory input, and storing new memories. The parietal lobe is superior to the occipital and temporal lobes; the left parietal lobe is involved in symbolic functions in language and mathematics, meanwhile, the right parietal lobe is devoted to spatial relationships. These lobes develop throughout the school years.

As we continue to move forward, we find the limbic system. The limbic system houses the emotional brain and includes, amongst other structures:

  • Amygdala — controls arousal, autonomic responses to fear, emotional responses, aggression, hormonal secretions. Involved in signaling for social interactions, including mating.

  • Hippocampus — involved in consolidation of new memories, formation of long-term memories, emotions, and spatial orientation.

  • Cingulate gyrus — coordinates sensory input with emotions and emotional response to pain. Also regulates aggressive behavior and attentional processing.

  • Nucleus accumbens — involved in reward, pleasure, and addiction.

These subcortical limbic systems begin developing during childhood and are almost completely developed by adolescence.

Finally, we come to the front and the most advanced part of the brain, the frontal lobes. The frontal lobe coordinates speech, thought, and short term memory storage. It helps progress from concrete to abstract thinking. The most anterior part of the frontal lobes is called the prefrontal cortex and is associated with cognitive control and managing emotion. This holds executive function and is responsible for planning, prioritizing, and complex decision making. The prefrontal cortex is the last brain region to fully develop, with maturation continuing through the teen years and completing development in the 20s. As the frontal lobes mature, the ability to regulate impulsivity and make better goal-oriented choices improves.

Therein lays the adolescent dilemma. Teens have an overactive pleasure seeking center (the limbic system) without supervision of the risks/benefits center (frontal lobe).  Decisions are made on impulse and emotion. This means that when a risky choice has a strong emotional incentive, such as winning the acceptance of peers, the limbic system is strongly activated. The emotional, incentive-driven limbic system wins over the immature prefrontal control system, and a risky choice is made.

Why would evolution support this asynchronous brain development?

This has been found in animal models, with structures of the limbic system maturing earlier than those of the frontal cortex in many species. During the time between birth and leaving the nest (the animal adolescence), many animal species become more socially active with peers, have conflict with their parents, and are more likely to engage in exploration and risk-taking behaviors. This developmental pattern may have evolved to foster independence and promote leaving family and village to find a mate. Adolescence is, after all, the transition period from childhood to adulthood.

How did I survive adolescence?!  How do I make sure my teen survives adolescence?!

The good news is that most survive adolescence relatively unscathed.  Experimentation is normal at this age. Let your teen make some mistakes. Set firm rules but also let your teen know that you are going to listen to whatever concerns they have. Model good decision-making. The most important thing is to not only punish them when they make a poor decision, but also praise them when they make the occasional good decision. Every risk is also an opportunity for growth.