Scientists have found a direct link between the number of "friends" a person has on Facebook and the size of certain brain regions, raising the possibility that using online social networks might change our brains.
The four brain areas involved are known to play a role in memory, emotional responses and social interactions.
So far, however, it is not possible to say whether having more Facebook connections makes particular parts of the brain larger or whether some people are simply pre-disposed, or "hard-wired", to have more friends.
"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," said Ryota Kanai of University College London (UCL), one of the researchers involved in the study.
Kanai and colleagues used magnetic resonance imaging (MRI) to study the brains of 125 university students, all of them active users of social media site Facebook, and cross-checked their findings in a further group of 40 students.
They discovered a strong connection between the number of Facebook friends and the amount of "grey matter" in the amygdala, the right superior temporal sulcus, the left middle temporal gyrus and the right entorhinal cortex. Grey matter is the layer of brain tissue where mental processing occurs.
The thickness of grey matter in the amygdala was also linked to the number of real-world friends people had, but the size of the other three regions appeared to be correlated only to online connections.
The students, on average, had around 300 Facebook friends, with the most connected having up to 1000.
With more than 800 million active users worldwide, Facebook has become a major component of social interaction, especially among the young.
"Online social networks are massively influential, yet we understand very little about the impact they have on our brains. This has led to a lot of unsupported speculation the Internet is somehow bad for us," said Geraint Rees of UCL.
"This shows we can use some of the powerful tools in modern neuroscience to address important questions -- namely, what are the effects of social networks, and online social networks in particular, on my brain."
The study results were published on Wednesday in the journal Proceedings of the Royal Society B.
Heidi Johansen-Berg of the University of Oxford, who was not involved in the research, said the findings were intriguing but did not mean Facebook was a short cut to making people brainier.
"If you got yourself 100 new Facebook friends today then your brain would not be bigger tomorrow," she said. "The study cannot tell us whether using the Internet is good or bad for our brains."
