Scientists have found a direct link between the number of Facebook friends a person has and the size of particular brain regions.
In the research, published today in the journal Proceedings of the Royal Society B, Professor Geraint Rees and Dr Ryota Kanai of University College London (UCL) demonstrate that the more Facebook friends a person has, the more friends they have in real life.
"Online social networks are massively influential, yet we understand very little about the impact they have on our brains," says Rees. "This has led to a lot of unsupported speculation the internet is somehow bad for us."
"Our study will help us begin to understand how our interactions with the world are mediated through social networks. This should allow us to start asking intelligent questions about the relationship between the internet and the brain - scientific questions, not political ones."
The study, funded by the Wellcome Trust, looked at brain scans of 125 university students who were active Facebook users, and compared them against the subjects' network of online and real-life friends. The findings were then replicated in a further group of 40 students.
The researchers found a strong correlation between a person's number of Facebook friends and the amount of grey matter - the tissue where processing is carried out - in several regions of their brain. One of the key regions is the amygdala, which is associated with processing memory and emotional responses. Another recent study linked the a large amygdala with a larger network of real-world friends.
Three other regions - the right superior temporal sulcus, the left middle temporal gyrus and the right entorhinal cortex - were also larger in those with lots of online friends, but didn't correlate with real-life friend networks. These regions are linked to the recognition and processing of biological and real-world signals.
Explaining the link, Dr Ryota Kanai said: "We have found some interesting brain regions that seem to link to the number of friends we have - both 'real' and 'virtual'. The exciting question now is whether these structures change over time - this will help us answer the question of whether the internet is changing our brains."