The bigger the network the bigger the amygdala

18. March 2011
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Those who have many other members of the species around them need a bigger brain to control all these relationships. That's what the "social brain" theory upholds. US brain researchers now show that the size of the amygdala is a measure of sociability in humans.

Facebook, Xing and other social networks make it possible to maintain contacts with colleagues and friends and establish new ones with two mouse clicks. For the person who wants to progress professionally, there is only one thing: networking. The person who is extrovert and not afraid to reach out to other people has it easier. While genome analysts still haven’t found the genes for this trait, it seems to neurologists that having a large circle of friends and acquaintances is reflected in the network of the central nervous system. The person who is well connected has an amygdala which is larger than the average. This is what pictures from Lisa Feldman Barrett from Boston show.

Her results support the “Social brain hypothesis“. According to this theory, the size of the brain goes with the increasing complexity of the relationship network associated to each individual. To manage all contacts and their requirements, we need an equally complex data processing center. In the center of the limbic system sits the amygdala, which reviews our sensory impressions and tells us what is good and bad, pleasant and unpleasant.

Little contact – smaller amygdala

What the research team has now found in humans was noticed previously by brain researchers in monkeys. The larger and more complex the network in the group, the more the volume of the amygdala also increased. In other animal species the rule also seems to apply: Whoever lives in a group needs not only a sophisticated visual center that processes the visual impressions but also needs links to sort the incoming data.

If the anatomy of species with an intense social life and those of loners can be differentiated, can the same apply for different character types in humans? For the answer to that question, Barrett and her team studied 58 men and women aged between 19 and 83 who had varying sizes of circles of friends and acquaintances. The researchers were interested not only in the number of regular contacts of their subjects, but also by how many different groups that they build up. In all examined brain regions only the amygdala showed a relationship between anatomical size in an MRI scan and the social network. For intensively socially-connected women and men, the computer on occasions calculated a size twice the 2.5 cubic millimeters of the more socially isolated, who had less than the specified five to fifteen regular contacts.

Amygdala damage removes fear

In old-age, contact tends to decrease. This was evident in statistics and in the amygdala size. But it remains unclear whether the size of this intimacy-network is the cause or consequence of having many contacts. “People differ in their ability,” Lisa Feldman Barrett believes, “to put faces and names in context with events. Someone with a large amygdala could more easily deal with the memorisation of these details.”

The idea hat the amygdala plays a central role in dealing with other people is not new. A member of a group of well-known American neurologists, Antonio Damasio, described a few years ago the case of a young woman with a bilateral lesion of this nerve center, who had lost all fear of other people. The woman even reacted to scary faces with great trust.

A study by Masahiko Haruno and Christopher Frith also offers information on the management of our acquaintanceships in the central nervous system. In the activity of the amygdala, the two researchers were able to identify which of the subjects were acting more out of fairness than acting in ways that were to their own advantage. Ultimately, Turhan Canli from New York already established in 2002 that outgoing people have a more active amygdala.

Virtual networks – not a substitute for real friends

Establishing a contact in a virtual network can be done within a few minutes. Whether one succeeds, however, in combatting loneliness with chats, forums and private messages is questionable. Because isolation in real life paves the way toward having virtual social networks in the first place, the lack of real friends will then become even greater, as Shima Sum of the University of Sydney and her colleagues showed in 2008. However, whoever uses “communities” in order to maintain his acquaintanceships has, with the computer, an effective remedy for loneliness. This applies not only for seniors but, a Dutch study shows , for young people as well.

Facebook in Germany counts, according to its own data, about 15 million users. With its help, could a timid, introvert person become a big-time networker? MRI images may soon provide that information. But data from the “Center for Digital Future” at the University of Southern California shows that the value of virtual networks for users is not in the aim of keeping them forever. In 2010 virtual networks had, for 38 percent of men under 40, just as great importance as contacts in real life. They are even more important for women, in whose case the percentage figure added up to 67 percent. How quickly that can change is demonstrated in a comparison with results in 2007. At that time the ratios for men and women were almost exactly the reverse.

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