TUESDAY, Oct. 18 (HealthDay News) -- People with lots of Facebook friends tend to have areas of the brain that are larger than those of online social network users with fewer friends, British researchers say.

"We were interested in understanding whether social networks and our participation in them is reflected in brain structure and function," lead researcher Dr. Geraint Rees, a Wellcome Trust Senior Clinical Research Fellow at University College London, said during a Tuesday press conference.

"What we've shown is an association between the number of friends on Facebook and certain areas of the brain and the structure of those areas," Rees said.

But, "a correlation doesn't imply causation," he added.

"Also, it is not clear whether the brain is hardwired for social networks," Rees said. "It could be that people have a large number of friends on Facebook simply because the structure of these brain regions is larger, but it could be the other way around -- that is, with people who have a large number of friends on Facebook, that might influence their brain structure. We cannot tell from this study alone which one of those two it is."

The study was published in the Oct. 18 issue of the Proceedings of the Royal Society B.

Facebook has more than 800 million active users worldwide, according to a university news release. People use it to keep in touch with their network of friends, but some networks are much larger than others. Some users have only a few friends while others have thousands, the researchers noted.

For the study, Rees and colleagues scanned the brains of 125 college students who used Facebook, then compared the scans with the number of online and real-world friends the students had. In addition, the researchers checked their finding with another group of 40 students.

Students in the study had an average of 500 friends on Facebook, but many had far fewer, Rees said.

The researchers found that the number of Facebook friends that students had correlated with the size of the gray matter in several areas of the brain.

One of the areas, the amygdala, is associated with memory and emotional responses. An earlier study found that this area was larger in people who had many real-world friends. Now it has been found that that's also true for those with lots of online friends, Rees said.

In addition, three other areas of the brain -- the right superior temporal sulcus, the left middle temporal gyrus and the right entorhinal cortex -- were also larger among those with lots of Facebook friends, but the size of these areas did not correlate with the number of real-world friends, the researchers noted.

The superior temporal sulcus affects the ability perceive moving objects. In addition to memory, the entorhinal cortex is associated with navigation -- including navigating through online social networks. The middle temporal gyrus plays a role in perceiving social cues, the researchers said.

Commenting on the study, Dr. Richard Isaacson, an associate professor of neurology at the University of Miami Miller School of Medicine, said that "there is evidence now for a biological basis behind the variability we have seen in social networking."

This finding could be part of the reason that some people are attracted to Facebook and some avoid it, he said. "Some people are really consumed by it; maybe we understand this a little better -- this is really cool stuff," he added.

More information

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