All those hours spent on Facebook may be making you gray. As in, the number of friends you have could be adding gray matter density to your brain. What this means is that the brains of people with large numbers of Facebook friends are different from those of people with fewer online connections.

These are the findings in a recent study by the University College London where researchers linked brain structure with Facebook activity.

The study, published in “Proceedings of the Royal Society B,” was based on MRIs of a group of 165 adults who were asked to report the number of Facebook friends they have, Mashable reported, noting the “study doesn’t delineate what is considered ‘high,’ though it refers to Dunbar’s Number, which postulates 150 friends is the limit of the average person’s social circle.”

Specifically, the report said the researchers found “variation in the number of friends on Facebook strongly and significantly predicted grey matter volume in left MTG, right STS and right entorhinal cortex.”

Because friends acquired in an online social network setting is different from those acquired through real-world social networks, it “raises a concern that the cognitive functions that support a large network size on Facebook may not necessarily correspond to those for offline, intimate social networks,” the report said. “Social networks for different functions (close friends, work colleagues, etc.) are organized at different scales up to the so-called ‘Dunbar number’ based on the correlation between cortical volume and group size across primate species, but these numbers are typically correlated across individuals.

In summarizing the results, the study concluded: “Taken together, our findings demonstrate that the size of an individual's online social network is closely linked to focal brain structure implicated in social cognition.”

Other such reports have indicated that social networks pose a danger for “brain drain” – causing children to form short attention spans or have an inability to be empathetic.

In a report from The Guardian, leading British neuroscientist Susan Adele Greenfield said that children’s experiences on social networking sites “are devoid of cohesive narrative and long-term significance. As a consequence, the mid-21st century mind might almost be infantilized, characterized by short attention spans, sensationalism, inability to empathize and a shaky sense of identity.”