New dimensions to the social brain: What’s So Social About the Social Brain?

1. New dimensions to the social brain:What’s So Social About the Social Brain? Robin Dunbar Department of Experimental Psychology University of Oxford

2. 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

3. Histological data The Social Brain Hypothesis Stephan et al (1981) An explanation for the evolution of unusually large brains in primates Evidence: Group size is a function of neocortex volume in three different datasets Dunbar (2010) Neocortex Ratio Histological data Fuster (1982) MRI data Rilling & Insel (1999) Prefrontal Cortex volume (cc) Neocortex grey matter volume (cc)

4. The Social Brain IS Costly Reaction Times Mentalising In the mentalising network, there is a parametric effect of task mentalising level on fMRI signal Factual Lewis et al.(submitted)

5. What Does the Social BrainPredict for Humans? • Predicted group size for humans is ~150 [Dunbar’s Number]

6. Are Human Groups 150? 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) Xmas Card Networks Hill & Dunbar (2003)

7. HumanSocial Groups These all 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 Doomsday 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 http://www.youtube.com/watch?v=ApOWWb7Mqdo “Reverse” Small World Experiments Killworth et al (1984) Hunter-Gatherer Societies Dunbar (1993) Luckily, it’s a hoax…. It was an advertising stunt! Individual Tribes Xmas Card Networks Hill & Dunbar (2003) Her 152 friends recorded for posterity…..?

8. The Social Brain is Really About…. The behavioural complexity of relationships ….group size is an emergent property Tactical Deception Coalitions Grooming clique size Partialling out phylogeny, body mass, etc by PGLS NO YES Dunbar & Shultz (2007) Byrne & Corp (2003) Kudo & Dunbar (2000)

9. The Fractal Periodicity of Group Sizes Xmas card dataset In all these mammals, scaling ratio  3 Social Groupings Database Xmas Card Database Hunter-gatherer groups Scaling ratio = 3.3 Hill, Bentley & Dunbar (2008) Zhou, Sornette, Hill & Dunbar (2005) Scaling ratio = exp(2π/) = 3.2 and 3.3 Hamilton et al (2007)

10. 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)

11. The Expanding Circles Intensity • 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? EGO 5 15 50 150 500 1500

12. How Bonding Works Bonding is a dual-process mechanism An emotionally intense component [= endorphins via grooming] A cognitive component [= cognition  brain size]

13. 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]

14. The Role of Social Cognition[Mentalising] • Intentional competence correlates with social network size …..Does the hardware correlate too? The Orders of Intentionality Scanner dataset Powell et al (2011) Stiller & Dunbar (2007)

15. 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)

16. 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 Neuroimaging Powell et al (2012) Lewis et al (2010)

17. Path Analysis of Imaging Data • There is a clear causal sequence: hardware  cognition [software]  behaviour Powell et al (2012)

18. 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)

19. 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

20. Grooming Time in Humans? • If we bonded our groups using the standard primate mechanism ….we would have to spend 43% of the day grooming

21. 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? Dunbar (1998)

22. How Grooming Works An experimental study with monkeys Opiates block social drive; Opiate-blockers enhance social drive • endorphins are relaxing • They create a psycho-pharmacological environment for building trust? Sal Keverne et al (1989)

23. 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]

24. The Three Ways We’ve Bridged the Gap Religion and its rituals Modern humans Archaic humans The Bonding Gap H. erectus Music and dance Australopiths Laughter a cross-cultural trait shared with chimpanzees

25. Music and Laughter Trigger Endorphin Uptake Dunbar et al (submitted A) Music Laughter Perform Comedy Control Edinburgh Fringe Dunbar et al (2012b) Singing Drumming Listening to vs vs listening music prayer vs video Neutral Dunbar et al (2012a) • Procedure: • pain test • video/activity • pain re-test Factual vs Comedy Videos

26. So….why not just get your kicks on your own? Plenty of people do…. …BUT doing it together seems to ramp up the effects

27. 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 Alone Group 2007 Boat Race Cohen et al (2010)

28. 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 Academy EPSRC ESRC Leverhulme Trust EU-FP7 ERC