Human Brain Volume Predicts Social Network Size
Sarah Loftus, 6th February 2012
The size of out social network may be determined by the size of our prefrontal corticies.
Photograph by Irene84 from nl, published under the GNU Free Documentation License
New evidence suggests that the size of a region of the brain
known as the orbital prefrontal cortex determines a person’s social ability and,
in doing so, determines the size of the social group an individual belongs to.
It is already known that primates have the largest brains of all vertebrates. One explanation for this is that maintaining the social group structure characteristic of primates is demanding on the brain. This theory is known as “the social brain hypothesis”. However, it is not brain size in general that determines the social network size in primates, instead it specifically relates to the size of a region of the brain called the neocortex, which forms the outer layers of the brain. In particular it seems to be attributed to the size of the front most regions of the neocortex, the prefrontal cortex (the region towards the back is generally associated with vision).
A research team made up of academics from Oxford, Liverpool, Manchester and Edinburgh universities, decided to see if the social brain hypothesis may be applied at an individual level rather than comparing whole species, examining whether the prefrontal cortex volume of individual humans reflects the size of the social group they belong to. They took a sample of 40 subjects and provided them with a questionnaire asking them to list the initials of everyone the participant had personal contact with or communicated with over the previous 7 days, excluding professional contacts (doctor, shopkeepers and teachers) unless the contact could explicitly be considered a genuine social interaction. They also assessed participants’ “intentionality competence”, a term used to describe the ability of a person to assess the intentions and mental states of others, i.e. their social ability. They also used MRI to scan subjects’ brains so that the volume of their prefrontal cortices could be determined. Statistical analysis was performed to determine whether there was a relationship between prefrontal cortex volume and social network size, also assessing whether any relationship was direct (i.e. prefrontal cortex size alone determines social network size) or that the intentionality competence resulting from prefrontal cortex size determined the relationship.
The results, published last week in Proceedings of the Royal Society B, show that there is a relationship between prefrontal cortex size, specifically the orbital region (roughly the region of the brain situated behind the base of the forehead and the eyes), and that this results from a person’s social ability (intentionality competence). The orbital prefrontal cortex has previously been shown to be involved in mood and behaviour involving emotions and feelings, and social aspects of thought. The study supports the claim that social behaviour is demanding on the brain and that this may have influenced its evolution, in part explaining why the brain volume of primates exceeds that of other vertebrates.
It is already known that primates have the largest brains of all vertebrates. One explanation for this is that maintaining the social group structure characteristic of primates is demanding on the brain. This theory is known as “the social brain hypothesis”. However, it is not brain size in general that determines the social network size in primates, instead it specifically relates to the size of a region of the brain called the neocortex, which forms the outer layers of the brain. In particular it seems to be attributed to the size of the front most regions of the neocortex, the prefrontal cortex (the region towards the back is generally associated with vision).
A research team made up of academics from Oxford, Liverpool, Manchester and Edinburgh universities, decided to see if the social brain hypothesis may be applied at an individual level rather than comparing whole species, examining whether the prefrontal cortex volume of individual humans reflects the size of the social group they belong to. They took a sample of 40 subjects and provided them with a questionnaire asking them to list the initials of everyone the participant had personal contact with or communicated with over the previous 7 days, excluding professional contacts (doctor, shopkeepers and teachers) unless the contact could explicitly be considered a genuine social interaction. They also assessed participants’ “intentionality competence”, a term used to describe the ability of a person to assess the intentions and mental states of others, i.e. their social ability. They also used MRI to scan subjects’ brains so that the volume of their prefrontal cortices could be determined. Statistical analysis was performed to determine whether there was a relationship between prefrontal cortex volume and social network size, also assessing whether any relationship was direct (i.e. prefrontal cortex size alone determines social network size) or that the intentionality competence resulting from prefrontal cortex size determined the relationship.
The results, published last week in Proceedings of the Royal Society B, show that there is a relationship between prefrontal cortex size, specifically the orbital region (roughly the region of the brain situated behind the base of the forehead and the eyes), and that this results from a person’s social ability (intentionality competence). The orbital prefrontal cortex has previously been shown to be involved in mood and behaviour involving emotions and feelings, and social aspects of thought. The study supports the claim that social behaviour is demanding on the brain and that this may have influenced its evolution, in part explaining why the brain volume of primates exceeds that of other vertebrates.
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