It is late in the evening rush hour, typical stop-and-go traffic. Finally, there is a break; the tightly packed group around you is soon cruising together at 55 mph. Suddenly, you see brake lights flare up ahead. As you prepare to brake, you glance in the rearview mirror and see an alarming sight--a car closing way too fast on your rear fender. The teenage driver looks panicked, one hand clutching the steering wheel, the other hand clenching a cell phone. You brace for the terrible impact...
We are quick to blame adolescents for getting themselves into predicaments that adults believe could be easily avoided. But recent research indicates that simple irresponsibility may not be the full explanation. When teenagers perform certain tasks, their prefrontal cortex, which handles decision making, is working much harder than the same region in adults facing the same circumstances. The teen brain also makes less use of other regions that could help out. Under challenging conditions, adolescents may assess and react less efficiently than adults.
Understanding the capabilities and limitations of the brain at different developmental stages is crucial for education and psychological assessment. Ironically, although the teenage years are widely recognized as a period of tremendous growth and change, the mental capabilities of teens have been less studied than those of children or adults. As more work is completed, it is becoming apparent that society should not be fooled into thinking that a teen has the mental prowess of an adult just because he or she looks and, most of the time, behaves like one. Brain processes that support cognitive control of behavior are not yet mature. Add stressors to the mix--like a sudden highway jam--and a teen can be an accident waiting to happen.
As recent studies underscore, differences in the prefrontal cortex--responsible for the so-called executive function that underlies planning and voluntary behavior--may be one of the most important distinctions between adolescents and adults. Beatriz Luna, director of the Laboratory of Neurocognitive Development at the University of Pittsburgh, has pinpointed differences by scanning the brains of teens and adults with functional magnetic resonance imaging (fMRI) during demanding tests of the visual-motor system.
In one setup, subjects faced a computer that flashed lights randomly. They were told either to rapidly focus on the lights or to try to avoid looking at them. Luna found that, when trying to block a strong reflexive tendency and make a considered response, "teens used more of their prefrontal cortex resources than adults did." Indeed, the amount of prefrontal cortex employed was similar to what adult brains use when performing a much more complex task. This excessive reliance, Luna says, "can lead to error, especially when difficulty increases."
Psychologists distinguish between two types of behavior control: exogenous and endogenous. Exogenous control is reflexive, generated in response to external stimuli--for example, focusing on lights as they appear on the screen. Endogenous control is voluntary and generated by an internal plan--trying not to look at the lights. A mature prefrontal cortex makes it easier for endogenous behavior to override exogenous behavior. In the traffic scenario, the exogenous response of the teen who suddenly realizes he is going to hit your rear bumper would be to freeze and scream, whereas the endogenous response would be to brake hard and steer out of the way. But for teen brains, deliberately overriding the exogenous reaction is more difficult than it is for adult brains.
Experts such as Luna maintain that although adolescents can at times demonstrate adult-level cognitive control of decision making, this endogenous power is only beginning to mature. In the visual-motor tests, she explains, subjects must use the prefrontal cortex to tell the rest of the brain how to behave. "Adolescents show similar capabilities of inhibition compared with adults, but the fMRIs show that they are using up prefrontal cortex like crazy," Luna notes. Adults call on other parts of the brain "to collaborate and better distribute the workload," she adds.