New dimensions to the social brain:

What’s So Social About the Social Brain?

Robin DunbarDepartment 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

The Social Brain Hypothesis

An explanationfor theevolution ofunusually largebrains in primates

Evidence:

Group size is a function ofneocortex volumein three different datasets

Prefrontal Cortex volume (cc)

Neocortex grey matter volume (cc)

Neocortex Ratio

Histological data

Histological data

MRI data

Dunbar (2010)

Stephan et al (1981)

Rilling & Insel (1999)

Fuster (1982)

The Social Brain IS Costly

Reaction Times

Mentalising

Factual

Lewis et al.(submitted)

In the mentalising network, there is a parametric effect of task mentalising level

on fMRI signal

What Does the Social BrainPredict for Humans?

• Predicted group size for humans is ~150

[Dunbar’s Number]

Are Human Groups 150?

All these have mean sizes of 100-200

Neolithic villages 6500 BC 150-200 Modern armies (company) 180Hutterite communities 107‘Nebraska’ Amish parishes 113business organisation <200ideal church congregations <200Domesday Book villages 150C18th English villages 160GoreTex Inc’s structure 150Research sub-disciplines 100-200

Small world experiments 134Hunter-Gatherer communities 148Xmas card networks 154

Maximum Network Size

350-374

325-349

300-324

275-299

250-274

225-249

200-224

175-199

150-174

125-149

100-124

75-99

50-74

25-49

0-24

Nu

mb

er

of

Ca

ses

10

9

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“Reverse”Small World Experiments

Killworth et al (1984)

Hunter-Gatherer Societies

Dunbar (1993)

Xmas Card Networks

Hill & Dunbar (2003)

HumanSocial Groups

These all have mean sizes of These all have mean sizes of 100-200100-200

Neolithic villages 6500 BC 150-200 Modern armies (company) 180Hutterite communities 107‘Nebraska’ Amish parishes 113business organisation <200ideal church congregations <200Doomsday Book villages 150C18th English villages 160GoreTex Inc’s structure 150Research sub-disciplines 100-200

Small world experiments 134Hunter-Gatherer communities 148Xmas card networks 154

Maximum Network Size

350-374

325-349

300-324

275-299

250-274

225-249

200-224

175-199

150-174

125-149

100-124

75-99

50-74

25-49

0-24

Nu

mb

er

of

Ca

ses

10

9

8

7

6

5

4

3

2

1

0

“Reverse”Small World Experiments

Killworth et al (1984)

1

10

100

1000

10000

0 10 20 30

Hunter-Gatherer Societies

Dunbar (1993)

Xmas Card NetworksHill & Dunbar

(2003)

Individual Tribes

Her 152 friends recorded for posterity…..?

http://www.youtube.com/watch?v=ApOWWb7Mqdo

Luckily, it’s a hoax….It was an advertising stunt!

The Social Brain is Really About….

Byrne & Corp (2003)

Grooming clique size

Kudo & Dunbar (2000)

YesNo

Coalitions

0.20

0.15

0.10

0.05

0.00

-0.05

Rel

ativ

e n

eoco

rtex

siz

e

Error bars: +/- 1.00 SE

Dunbar & Shultz (2007)

Coalitions

NO YES

Partialling out phylogeny, body mass, etc by PGLS

Tactical Deception

The behavioural complexity of relationships

….group size is an emergent

property

The Fractal Periodicity of Group Sizes

Xmas Card Database

Social Groupings Database

Scaling ratio = exp(2π/) = 3.2 and 3.3

Zhou, Sornette, Hill & Dunbar (2005)

Hamilton et al (2007)

Hunter-gatherer groups

Scaling ratio = 3.3

Hill, Bentley & Dunbar (2008)

In all these mammals,

scaling ratio

3

Xmas card dataset

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]

• The 150 = limit on personalised, reciprocated relationships

• 1500 = limit on memory for faces?

5

15

50

150

Intensity

EGO

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]

• Intentional competence correlates with social network size

…..Does the hardware correlate too? Level of intensionality

9th8th7th6th5th4th3rd2nd1st

Fre

quen

cy o

f fa

ilure

20

10

0

Level of intensionality

1086420

Cliq

ue s

ize

30

20

10

0Stiller & Dunbar

(2007)

Powell et al (2011)

Scanner dataset

The Orders of Intentionality

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)

• 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

Insights from Insights from NeuroimagingNeuroimaging

Powell et al (2012)

Lewis et al (2010)

Path Analysis of Imaging Data

• There is a clear causal sequence:

hardware cognition [software] behaviour

         

Powell et al (2012)

Networks Correlate with Brain Regions

Kanai et al. (2011)

Sallet et al. (2012)

Internet Friends

Social group size in

macaques

Just HOW are they doing this?

Why Time is Important

• Grooming as the bonding agent in primates

• Grooming time is determined by group size

• …with an upper limit at about 20% of total daytime

         

Group Size

160140120100806040200

So

cia

l Tim

e (

%)

50

40

30

20

10

0

Predicted for Humans

Grooming Time in Humans?

• If we bonded our groups using the standard primate mechanism

….we would have to spend 43% of the day grooming

         

Group Size

160140120100806040200

So

cia

l Tim

e (

%)

50

40

30

20

10

0

Predicted for Humans

Grooming Time in Humans?

• In fact, we spend only 20% of our time in social interaction…..from a sample of 7 societies from Dundee to New Guinea

• How do we bond our super-large communities?

         

Group Size

160140120100806040200

So

cia

l Tim

e (

%)

50

40

30

20

10

0

Predicted for Humans

Dunbar (1998)

How Grooming Works

• endorphins are relaxing

• They create a psycho-pharmacological environment for building trust?

         

Group Size

160140120100806040200

So

cia

l Tim

e (

%)

50

40

30

20

10

0

Predicted for Humans

0

2

4

6

8

10

12

Num

ber

of G

room

ing

Par

tner

s

Sal Naltrex Sal Morph

An experimental study with monkeys

Opiates block social drive;

Opiate-blockers enhance social drive

Sal

Keverne et al (1989)

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 β-endorphins]

• 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

Millions Years BP

3.53.02.52.01.51.0.50.0-.5

Pre

dict

ed G

room

ing

Tim

e (%

)

50

40

30

20

10

Laughter a cross-cultural trait

shared with chimpanzees

Music and dance

Religion and its rituals

Australopiths

Modern humans

H. erectus

Archaic humans

The Bonding

Gap

Procedure: Procedure: • pain test

• video/activity• pain re-test

Dunbar et al (submitted A)

Singing Drumming Listening to vs vs listening music prayer vs video

Factual vs Comedy Videos

Music

Laughter

EdinburghFringe

Neutral

Control

Perform

Comedy

Music and Laughter Trigger Endorphin Uptake

Dunbar et al (2012a)

Dunbar et al (2012b)

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?

Alone Group Alone Group

Change in pain threshold before and after 45 mins

rowing work-out on ergometers in the gym:

Alone vs in a virtual boat

2007 Boat Race

Cohen et al (2010)

With Thanks to….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

For funding:

British AcademyEPSRCESRCLeverhulme TrustEU-FP7ERC