Why adolescents put themselves first

Teenagers are more selfish than adults because they use a different part of their brain to make decisions compared to adults, new research suggests.

Previous work has shown that when children reach puberty, there is an increase in connections between nerves in the brain. This occurs particularly in the area involved in decision-making and awareness of other people’s feelings, called the "mentalising network".

Now Sarah-Jayne Blakemore, a cognitive neuroscientist from University College London, UK, has used functional magnetic resonance imaging (fMRI) to scan the brains of 19 adolescents (aged 11 to 17) and 11 adults (aged 21 to 37) whilst they were asked questions relating to decision-making. Questions such as: “You’re going to the cinema, where do you look for film times?”

Blakemore found that teenagers rely on the rear part of the mentalising network to make their decisions, an area of the brain called the superior temporal sulcus. In contrast, adults use the front part, called the prefrontal cortex.

The superior temporal sulcus is involved in processing very basic behavioural actions, whereas the prefrontal cortex is involved in more complex functions such as processing how decisions affect others. So the research implies that "teenagers are less able to understand the consequences of their actions", says Blakemore.

Taken care of

In a separate experiment, Blakemore asked 112 participants (aged from 8 to 37) to make decisions about other people’s welfare and timed how long it took them to respond. The questions included: "How would your friend feel if she wasn’t invited to your party?"

She found that the response time got shorter as the participants got older, suggesting that the older people found it easier to put themselves in other people's shoes.

Blakemore suggests that both findings might be explained by an evolutionary mechanism in which the development of the brains of adolescents takes precedence over its performance. “You don’t need to be on a par with other people because you are looked after until reproductive age. Only then do you need to start to take into account other people’s perspectives.”

Work in progress

The work has implications for the types of responsibility given to adolescents, Blakemore says: “Teenager’s brains are a work in progress and profoundly different from adults. If you’re making decisions about how to treat teenagers in terms of the law, you need to take this new research into account.”

Sam Lewis, a specialist in youth crime and justice, from the University of Leeds, says there has in fact been a shift away from welfare-focused approaches to youth punishment in the UK: “Today, responses to youth crime tend to emphasise offender responsibility, accountability and punishment. It seems likely that the concerns of many, including those of Dr Blakemore, may be lost in the tide of punitive policies being pursued by the government.”

The research was presented at the British Association for the Advancement of Science Festival in Norwich, UK.

Source: New Scientist