What’s So Social About the
Social Brain?
Robin Dunbar
Department of Experimental Psychology
University of Oxford
Social Cognitive
Neuroscience
A Challenge
•
•
•
SCN has become one of the big
stories in neuropsychology and
neuroimaging
But what exactly is the nature of
sociality in this context?
The Challenge: Have we focussed
on the right indices of sociality?
•
Sociality typically viewed as a dyadic
interaction
•
But in fact it is about relationships in
complex networks
Histological
data
Stephan et al (1981)
The Social Brain
Hypothesis
Dunbar (2010)
Neocortex Ratio
An explanation
for the
evolution of
unusually large
brains in primates
Histological
data
Fuster (1982)
MRI data
Rilling & Insel (1999)
Evidence:
Group size is
a function of
neocortex volume
in three different datasets
Prefrontal Cortex volume (cc)
Neocortex grey matter volume (cc)
The Social Brain
IS Costly
Reaction Times
Mentalising
Factual
In the mentalising network, there is a
parametric effect of task mentalising level on
fMRI signal
Lewis et al.(submitted)
What Does the Social Brain
Predict for Humans?
• Predicted group size for
humans is ~150
[Dunbar’s Number]
All these have mean sizes of
100-200
Neolithic villages 6500 BC 150-200
Modern armies (company)
180
Hutterite communities
107
‘Nebraska’ Amish parishes
113
business organisation
<200
ideal church congregations
<200
Domesday Book villages
150
C18th English villages
160
GoreTex Inc’s structure
150
Research sub-disciplines 100-200
Small world experiments
134
Hunter-Gatherer communities 148
Xmas card networks
154
“Reverse”
Small World
Experiments
Killworth et al (1984)
Hunter-Gatherer
Societies
Dunbar (1993)
10
9
8
Number of Cases
Are Human Groups
150?
Xmas Card
Networks
6
5
4
3
2
1
35
32
30
37
0-
34
5-
32
0-
29
5-
27
0-
24
5-
22
0-
19
5-
17
0-
14
5-
4
9
4
9
4
9
4
9
4
9
4
Maximum Network Size
27
25
22
20
17
15
12
9
-9
4
-7
9
-4
12
0-
75
50
24
0-
10
0
25
Hill & Dunbar (2003)
7
Human
Social Groups
http://www.youtube.com/watch?v=ApOWWb7Mqdo
“Reverse”
Small World
Experiments
Killworth et al (1984)
These all have mean sizes of
100-200
10000
Neolithic villages 6500 BC 150-200
1000
Modern armies (company)
180
Hunter-Gatherer
Hutterite communities
107
Societies
100
‘Nebraska’ Amish parishes
113
Dunbar (1993)
business organisation
<200
10
ideal church congregations
<200
Doomsday Book villages
150
Luckily,
Individual Tribes
C18th English villages
160 it’s a 1hoax….
0
10
20
30
stunt!
GoreTex Inc’s structure
150 It was an advertising
Research sub-disciplines
100-200
10
9
Xmas Card
Networks
7
6
5
4
3
for posterity…..?
1
35
32
30
37
0-
34
5-
32
0-
29
5-
27
0-
24
5-
22
0-
19
5-
17
0-
14
5-
4
9
4
9
4
9
4
9
4
9
4
Maximum Network Size
27
25
22
20
17
15
12
9
-9
4
-7
9
-4
12
0-
75
50
10
0
24
0-
Hill & Dunbar (2003)
2
25
Small world experiments
134
Hunter-Gatherer communities 148
friends recorded
XmasHer
card 152
networks
154
Number of Cases
8
The Social Brain is Really About….
The behavioural
complexity of
relationships
….group size is
an emergent
property
Grooming clique size
Tactical Deception
0.20
Coalitions
Relative neocortex size
0.15
0.10
0.05
Partialling out
phylogeny, body
mass, etc by
PGLS
0.00
-0.05
No
Yes
Coalitions
NO
Error bars: +/- 1.00 SE
Byrne & Corp (2003)
Kudo & Dunbar (2000)
YES
Dunbar & Shultz (2007)
The Fractal Periodicity
of Group Sizes
Xmas card
dataset
In all these
mammals,
scaling ratio
3
Social Groupings
Database
Xmas Card
Hunter-gatherer
Database
groups
Hill, Bentley & Dunbar
(2008)
Zhou, Sornette, Hill & Dunbar (2005)
Scaling ratio = exp(2π/)
= 3.2 and 3.3
Scaling ratio = 3.3
Hamilton et al (2007)
Social Complexity in
Primates
• Primate societies are
hierarchically embedded
• As neocortex size increases,
groups become socially more
fragmented (grooming cliques
get smaller)
• Somehow, they manage to
balance a two-tier system
Lehmann & Dunbar (2009)
The Expanding
Circles
• Our relationships form a
hierarchically inclusive
series of circles of
increasing size but
decreasing intensity
[ie quality of relationship]
Intensity
EGO
5
15
•
The 150 = limit on
personalised, reciprocated
relationships
• 1500 = limit on memory for faces?
50
150
500
1500
How Bonding Works
Bonding is a dual-process
mechanism
 An emotionally intense
component
[= endorphins via grooming]
 A cognitive component
[= cognition  brain size]
The Limits to Intentionality...
A natural limit at 5th order
intentionality:
“I intend that you believe
that Fred understands
that we want him to be
willing to [do
something]…” [level
5]
The Role of Social Cognition
[Mentalising]
The Orders of Intentionality
•
Frequency of failure
20
10
Intentional competence correlates with
social network size
…..Does the hardware correlate too?
0
1st 2nd 3rd 4th 5th 6th 7th 8th 9th
Level of intensionality
30
Clique size
Scanner dataset
20
10
Powell et al
(2011)
Stiller & Dunbar (2007)
0
0
2
4
6
8
Level of intensionality
10
Intentionality and
Frontal Lobe Volume
3T T1-weighted MRI
Howard et al’s (2003) parcellation method,
using Cavalieri method for estimating volumes
PFC defined by leading edge of corpus
callosum
Intentionality correlates with
orbitofrontal PFC, but not with
dorsal frontal
Powell et al (2010)
Insights from
Neuroimaging
Powell et al (2012)
•
In a stereological analysis of gross volume:
best predictor of BOTH intentional
competence and network size is
orbitofrontal PFC volume
•
In a fine-grained VBM (voxel) analysis:
overlap of network size and intentional
competence in the ventromedial PFC
Lewis et al (2010)
Path Analysis of Imaging Data
Powell et al (2012)
• There is a clear causal sequence:
hardware  cognition [software]  behaviour
Networks
Correlate with
Brain Regions
Social group
size in
macaques
Internet Friends
Sallet et al. (2012)
Just HOW are they doing this?
Kanai et al. (2011)
Why Time is Important
50
Social Time (%)
• Grooming as the
bonding agent in
primates
• Grooming time is
determined by
group size
Predicted for Humans
40
30
20
10
• …with an upper
limit at about 20%
of total daytime
0
0
20
40
60
80
100
Group Size
120
140
160
Grooming Time in Humans?
Social Time (%)
• If we bonded
our groups
using the
standard
primate
mechanism
….we would have
to spend 43%
of the day
grooming
50
Predicted for Humans
40
30
20
10
0
0
20
40
60
80
100
Group Size
120
140
160
Grooming Time in Humans?
Social Time (%)
• In fact, we spend only
20% of our time in
social interaction
…..from a sample of 7
societies from
Dundee to New
Guinea
50
Predicted for Humans
40
30
20
10
• How do we bond our
super-large
communities?
0
0
20
40
60
80
100
120
140
Group Size
Dunbar (1998)
160
How Grooming Works
12
Number of Grooming Partners
50
Predicted for Humans
Social Time (%)
40
30
20
10
An experimental
study with
monkeys
10
8
6
Opiates block
social drive;
4
2
0
Sal Naltrex
Sal
Sal Morph
0
0
20
40
60
80
100
120
140
160
Group Size
• endorphins are relaxing
• They create a psychopharmacological environment for
building trust?
Keverne et al (1989)
Opiate-blockers
enhance social
drive
μ-receptor Activation in Light Stroking
•
•
•
•
Preliminary results from a first PET study (at Turku, Finland)
Carfentanil as opiate antagonist with particular affinity to μ-receptors [for βendorphins]
Significant response in some key regions that suggest endorphin activation even
to light touch
Probably exploiting the same c-afferent fibre system as found widely in mammals
[responds ONLY to light touch as in stroking movements of grooming]
The Three Ways
We’ve Bridged
the Gap
Religion and its rituals
50
Modern humans
40
Archaic humans
The
Bonding
Gap
H. erectus
30
Music and dance
20
Australopiths
10
-.5
0.0
.5
1.0
1.5
2.0
2.5
3.0
3.5
Millions Years BP
Laughter
a cross-cultural trait
shared with chimpanzees
Music and Laughter Trigger
Endorphin Uptake
Dunbar et al (submitted A)
Music
Laughter
Perform
Comedy
Control
Edinburgh
Fringe
Dunbar et al (2012b)
Singing
vs
prayer
Drumming
Listening to
vs listening
music
vs video
Neutral
Dunbar et al (2012a)
Procedure:
•
pain test
•
video/activity
pain re-test
•
Factual vs Comedy Videos
So….why not just get your
kicks on your own?
Plenty of people do….
…BUT doing it together
seems to ramp up the
effects
Synchony Ramps
up the Endorphins?
Change in pain threshold
before and after 45 mins
rowing work-out on
ergometers in the gym:
Alone vs in a virtual boat
Alone
Group
2007
Boat
Race
Alone
Group
Cohen et al
(2010)
Comparative brains:
• Dr Susanne Shultz
• Dr Boguslaw Pawlowski
Social Networks and Bonding:
• Dr Sam Roberts
• Dr Russell Hill
• Prof Alex Bentley
• Dr Wei Zhou
• Prof Didier Sornette
• Dr Emma Cohen
• Dr Anna Machin
Imaging:
• Amy Birch
• Rachel Browne
• Dr Penny Lewis
• Dr Joanne Powell
• Dr Marta García-Fiñana
• Prof Neil Roberts
• Dr Lauri Numennmaa
With Thanks to….
For funding:
British Academy
EPSRC
ESRC
Leverhulme Trust
EU-FP7
ERC