How many Facebook "friends" do you have? People with lots of friends on the social networking site have denser grey matter in certain regions of the brain, says a new study, raising the possibility that such sites may be altering people's brains.

Researchers at University College London found that users with the greatest number of friends on Facebook had more grey matter in brain regions than those of people with fewer online connections.

Those brain regions are associated with creating memories of names and faces as well as how one interprets social cues such as gaze and body movements.

The findings, published in the journal Proceedings of the Royal Society B: Biological Sciences, suggested that either social networking changes these brain regions, or that people born with these kinds of brains behave differently on websites like Facebook.

"Social networks exist in many forms-- in the real world, in cyberspace and in many other forms. They are a particular aspect of human behaviour that surrounds and affects many aspects of how we live our daily lives," study author Geraint Rees was quoted as saying by LiveScience.

For their study, the researchers used functional magnetic resonance imaging to create brain scans of 125 healthy college students. They compared the sizes of various brain regions with each participant's number of Facebook friends and real life friends. They repeated the study on a separate group of 40 students.

They found a strong link 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.