Sarah-Jayne Blakemore, professor of cognitive neuroscience at University College London, said while there appeared to be an increase in mental-health problems among teenagers, no cause had been established.
“There is no scientific evidence about how screen time affects the developing brain,” she told RTÉ’s Sean O’Rourke.
“There seems to have been an increase in mental-health problems, including depression and anxiety, in adolescents and there has also been an increase in the use of screens and phones and social media, but that is a correlation. We don’t know if one causes the other.”
Her comments come as the education minister prepares to order schools to bring parents and students together to agree robust rules to limit smartphones in schools.
Unions have said most schools already have written policies on phone use but teachers admit they can be hard to implement.
The move has come amid growing concerns over the effects of social media on teenagers, with rising reports of cyberbullying, anxiety, eating disorders, and self-harm.
Prof Blakemore said increasing academic pressures and social pressures could equally be to blame.
I’m not saying that social media and mobile phones don’t contribute. It’s just that we don’t have any evidence yet of causal contribution to mental-health problems.
Prof Blakemore said traditional approaches to steering teenagers away from risky behaviour were ineffective.
She said public-health chiefs need to appeal to the rebel side of teenagers’ brains if they want them to heed warnings about their lifestyle choices.
In her new book, Inventing ourselves: The secret life of the teenage brain, she says that major changes take place in the brain during adolescence, in particular to the prefrontal cortex which controls self-awareness, social interaction, and decision-making.
“Most health advertising aimed towards teenagers will focus on the long-term health risks of things like what you eat, whether you smoke, whether you experiment with drugs or binge drink but there’s not a lot of evidence that that works because teenagers know about the health risks.”
She said for teenagers, those risks are nothing compared to the social risk of not doing the same as their friends, and they need to be empowered to stick up for themselves and say no to behaviour they don’t want to take part in.
Another good ploy is to appeal to their anti-establishment instincts, pointing out to them that the goods or services they consume are making someone else rich.
“You tell them that this is an industry which is trying to manipulate them and get them addicted and they are just lining the pockets of adults who run these industries. That somehow taps into something that adolescents don’t like and works better.”