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Social Brains

We are social beings
by

Dr. H. C. Sinclair

on 18 August 2016

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Transcript of Social Brains

The Social Brain
The Social Brain Hypothesis
(Dunbar, 1993)
Only the Lonely...
Chronically lonely individuals have less grey matter in the left posterior superior temporal sulcus (pSTS)? (Kanai et al., 2012)
Translation: They have difficulty with processing basic social cues
Why do primates - especially humans - need larger brains than other species to do the same jobs?
More than just termites & nuts
"...primates large brains reflect the computational demands of the complex social systems..."
"...the social brain hypothesis has found near universal acceptance as the best explanation for the evolution of extensive variation in brain size among mammals
(van Schaik, et al., 2012, p. 277)."
The Brain is Social
Facebook on the Brain
“…the number of friends an individual declares on a web-based social networking service reliably predicted grey matter density in the right superior temporal sulcus, left middle temporal gyrus, and entorhinal cortex. (Kanai et al., 2012, pg. 1327)”
Areas for social perception (particularly understanding social intentions) and associative memory (for relationships).
Social group size is correlated with neocortex volume across primate species
Dunbar's number...
Built off of the "Machiavellian Intelligence Hypothesis"
The neocortex ratio of a species is the ratio of the size of the neocortex to the rest of the brain.
The larger your social network, the greater the volume of your amygdala (associated with the emotional coding of social signals). - Bickart et al., 2010
Gotta have friends....
But correlation does not equal causation
Monkey business
Their analysis revealed a clear, linear relationship between the size of a monkey’s social network and an increase of neocortical gray matter in regions involved with social cognition (such as the mid-superior temporal sulcus, rostral prefrontal cortex as well as the frontal and temporal cortex).
The monkeys demonstrated an expansion of gray matter ranging from 3-8% (depending on the brain region) for each additional member of their social network.
In other words, monkeys that lived in the most socially complex group had an average increase of 20% more neocortical growth than monkeys housed individually.
Sallet & Rushworth, 2011
+
Egg? Chicken? Social Network
A familiar tale....
Harlow, 1958
Social Deprivation
The isolated monkeys grew up with severe emotional and behavioral problems, developing an "autistic-like" syndrome, with grooming, self-clasping, social withdrawal, and rocking.
As for humans....
"The Lost Children of Romania"
Social deficiencies
Cognitive deficiencies
Heightened Cortisol
Reduced Oxytocin
Death
Understanding
Trust
Belonging
Control
Self-esteem
FISKE's
FIVE CORE SOCIAL MOTIVES
These associations are unique to online "friends"
Other Considerations
And it is more than just Machiavellian
But it doesn't just extend to primates
And dolphins & whales...(Marino, 1996)
And bats...(Barton & Dunbar, 1996)
And hyenas...(Sakai et al., 2011)

Now consider that the average individual social network size around 150 for humans
The neocortex ratio for humans is CR=4.1.
Your brain needs a social life to have a life!
In sum...
vs. the "Ecological Hypothesis" vs. ....
Mapping the Brain
Brains are expensive
"The human brain weighs about 2% of body weight but consumes 20% of total energy intake..."
"Because the cost of maintaining a large brain is so great it is intrinsically unlikely that large brains will evolve merely because they can. Large brains will evolve only when the selection factor in their favor is sufficient to overcome the steep cost" (Dunbar, 2006, pg. 179)
What's worth it?
Must always consider the costs vs. benefits, the constraints vs. facilitators - both from the environment AND the affected.
Compared to 7-8% in other primates
Expensive Tissue Hypothesis
In order to feed our growing brains, humans diverged from primates with regard to how much energy (e.g., glucose) was devoted to the brain over brawn. (Fedrigo et al., 2011).
But that still doesn't explain WHY the change in energy allocation occurred?
"...it is expensive tissue which uses up to 80% of resting metabolic rate in the newborn and continues to use almost 50% of it during the first 5 postnatal years." - Judas et al., 2013, pg. 1
Especially Expensive
During Development
Sample Question
Will it be on the test? Possibly.... and if not this, something like it.
If I were an evolutionary psychologist and I believed that human neocortex size was due to humans needing to develop the brain capacity to make tools and track down increasingly hard-to-get foods, I would endorse which theory?
A. The Social Brain hypothesis
B. The Machiavellian Intelligence hypothesis
C. The Expensive Tissue hypothesis
D. The Ecological hypothesis
Sample Question
Will it be on the test? Possibly.... and if not this, something like it.
The size of a dolphin’s brain is approximately 1603 cc on average. The dolphin’s neocortex is approximately 1279 cc. What is the dolphin’s neocortex ratio?
A. 1.25
B. 3.94
C. 39%
D. 324

And hopefully I don't need to make an argument that you need a brain...
Evolution would be so proud...
What is the social brain hypothesis?
What are any alternatives to the social brain hypothesis?
How do you compute a neocortex ratio? And how is it linked to network size?
What is the human neocortex ratio?
What is Dunbar’s number?
What evidence is there that relationships affect brain development?
What parts of the brain have been shown to be affected by the quantity of our social connections?
What did Sallet & Rushworth do? What did they find with regard to network size and gray matter? How much more neocortical growth was there for those with larger networks?
What is marasmus (or failure to thrive)? And what are the impacts of social deprivation (on cortisol? Oxytocin?)
How are different parts of the brain (e.g., amygdala, the pSTS, entorhinal cortex associated with social cognition and social perception?
What are the functions of the different parts of the brain associated with social network size and the self?
Some things you should know now...
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