Remember that Facebook friend request you got from an elementary school classmate you don't remember? Good thing you accepted it.

New research shows a direct link between the number of Facebook "friends" and brain size.

A study conducted at University College London found that social networking users with the greatest number of online friends had more gray matter in part of their brains, according to findings published this week in the British biological research journal, Proceedings of the Royal Society.

The brain regions with more gray matter, according to the paper, included those affecting the creation of memories of faces and names, and those that help us social cues, such as body language.

"Our findings demonstrate that the size of an individual's online social network is closely linked to focal brain structure implicated in social cognition," researchers said.

The researchers questioned 125 college students about their Facebook friends while conducting magnetic resonance imaging to create brain scans, then repeated the study on another group of participants. The study also considered the number of Facebook "friends" versus real-life friends.

Researchers admit in the study that there's no way to know if some people are just "wired" to be more social.