Monday October 23, 2017 Q&A

In teens, delayed development of the prefrontal cortex causes...


1 Chronic fatigue

2 Confusion between left and right

3 Difficulty identifying facial expressions

Correct answer: 3, difficulty identifying facial expressions.

Neuroscientists have made major strides in understanding brain development thanks to modern imaging techniques. Magnetic resonance, which produces images of the brain as it functions, has now revealed insights into cerebral development during the transition years of adolescence. According to scientists, two regions of the brain – the prefrontal cortex and the limbic system – develop at different rates during the period between childhood and adulthood.

The limbic system includes several areas of the brain, such as the hippocampus, both amygdalae and the insular cortex, which play an important role in memory and processing emotional stimuli. It also connects certain areas linked to the endocrine system and hormonal secretion.

Various studies have shown that the limbic system is highly active and even hypersensitive in the early stages of puberty, i.e., 12 to 13 years old. This would explain why many teens tend to seek out intense sensations – all the more so as the prefrontal cortex, which controls executive functions like decision-making, organization, forethought, judgment and impulse control, fully matures much later. Indeed, the prefrontal cortex can undergo significant changes even past the age of 20. Adolescence is therefore marked by asynchronous development between the limbic system and the prefrontal cortex, likely driving teens to take more risks at a time when their prefrontal cortex is still maturing.

Emotional response

The delay in maturation also affects teens’ ability to understand other people's intentions and emotions. A study carried out by researchers at McLean Hospital in Belmont, Massachusetts, found that adults and teens diverge sharply in their ability to decipher another person's facial expressions: teens are more likely to slightly or completely misinterpret facial expressions.

MRIs showed that the two groups use different parts of their brain to carry out this task. Adults activate a part of their prefrontal cortex, whereas 12- to 17-year-olds use predominantly their amygdalae.

Yet the main function of the amygdalae, which are located in the center of the brain, is to identify potential threats and send out alerts. As a result, they are associated with fear and anxiety. But, they are also linked to the creation of positive emotions, stemming primarily from the dopaminergic pathway that connects with the nucleus accumbens in the ventral striatum, which plays a key role in the reward system.

When faced with certain facial expressions or displays, an adolescent will therefore tend to not only interpret them incorrectly, but also respond to them more emotionally than an adult would.

Thanks to Olivier Jorand, PhD and researcher in neuroscience at the University of Fribourg.