Brain circuits linked to gambling and chocolate are activated when teenagers use social media, according to a new study.
The UCLA study scanned the brains of teenagers aged between 13 and 18 while they looked at a social network that resembled Instagram.
The teens looked at 148 photos for around 10 minutes - including 40 they had submitted themselves - while they underwent fMRI scans.
Each photo showed the number of interactions it had received from other 'participants', which in reality were actually assigned by the researchers.
Once the teenagers saw likes on their own photos, "activity across a wide variety of regions in the brain" was seen, according to lead researcher Lauren Sherman.
"A region that was especially active was a part of the striatum called the nuclear accumbens," she explained. This is part of the brain's "reward circuitry", which is "particularly sensitive during adolescence".
It was this region that was activated when the teenagers saw the photos with a large number of likes.
Teenagers brains also became more activated when they saw 'risky' photos, containing cigarettes, alcohol or other provocative imagery, than when they saw 'neutral' photos.
When viewing the 'risky' photos, they had "less activation in areas associated with cognitive control and response inhibition", including the dorsal anterior cortex, the bilateral prefrontal cortices and lateral parietal cortices.
The number of likes a photo had also had an influence on whether the teens decided to like it or not.
"We showed the exact same photo with a lot of likes to half of the teens and to the other half with just a few likes," Sherman said. "When they saw a photo with more likes, they were significantly more likely to like it themselves. Teens react differently to information when they believe it has been endorsed by many or few of their peers, even if these peers are strangers."
This influence isn't just online - the influence of social groups in 'real' life is likely to be "even more dramatic".
"In the study, this was a group of virtual strangers to them, and yet they were still responding to peer influence; their willingness to conform manifested itself both at the brain level and in what they chose to like," said Mirella Dapretto, who worked on the study and is a professor of psychiatry at UCLA.
"We should expect the effect would be magnified in real life, when teens are looking at likes by people who are important to them."
This also means teenagers need to be careful who they interact with online, said the study authors.
"It's important for parents to be aware of who their teens interact with online and what these friends and acquaintances are posting and liking," said Patricia Greenfield, director of UCLA's Children's Digital Media Center.
"In addition, teens' self-identity is influenced by the opinions of others, as earlier studies have shown. Our data certainly seem to reflect that as well."
The study has been published in Psychological Science.
This article was originally published by WIRED UK
