Comparing Social Cognitive, Non-Social Cognitive, and Resting Brain Activity in Chimpanzees (Pan troglodytes) Open Access
Barks, Sarah Kate (2010)
Abstract
The evolution of the human brain and cognition represents a
long-standing question of
biological anthropology. Skillful interaction with others has been
proposed as a primary mover
behind increased intelligence in primates (Dunbar 1998). This study
explores the origins of the
neural bases of social cognition in humans, asking whether human
patterns of social cognitive
brain function are unique to our species, or shared with
chimpanzees (Pan troglodytes). Using
[18F]-fluorodeoxyglucose positron emission tomography, chimpanzee
brain function was assessed
during a social cognition task, a non-social cognition task, and at
rest. Two primary aims are to
assess the degree to which social cognitive brain function is
similar to resting brain function in
chimpanzees, and to examine the neural correlates of chimpanzee
social cognition. Similar
patterns of function to those of humans would suggest that these
social cognitive networks were
present in our last common ancestor. Conversely, if patterns of
activation differ, these species
may have diverged in this regard.
Chimpanzees performed a match-to-sample task with videos depicting
conspecific
behaviors with varying social complexity. Functional neuroimaging
data obtained during these
task conditions were compared with data from a non-social condition
and a resting condition.
These conditions were compared both qualitatively and on a
voxel-by-voxel basis using paired t-
tests.
Like the resting state, social cognition in chimpanzees activates
cortical midline
structures, including the precuneus, posterior cingulate, and
medial prefrontal cortex. Social
cognition also activates the insula and amygdala; higher levels of
social complexity activate the
ventral striatum. At rest, these areas are active to a greater
degree. Whole brain averages of each
condition examined independently show the same cortical midline
areas of greatest activation
across all conditions. Rest, however, produces a higher maximum
activation and a wider spread
of intensity.
This study bolsters previous findings that the resting state in
chimpanzees shows similar patterns of brain activity as that of
humans, with cortical midline structures highly
active, and shows that these areas consistently deactivate in a
variety of task conditions much like
the human default network. Further, these data demonstrate
similarity in brain function during
social cognition and at rest in chimpanzees.
Table of Contents
Table of contents
List of figures and tables
Introduction 1
Chapter 1: Background 4
Human social cognitive neuroscience 4
Theory of mind 4
Anatomy of theory of mind 5
Theory of mind and imitation 8
Development of theory of mind 11
The default mode network 13
The default mode network and social cognition 16
Chimpanzee social cognition 17
Social structure in the wild 18
Social learning 21
Social cognitive capacities 23
Self-awareness 24
Deception and false belief 25
Joint attention 27
Theory of mind in chimpanzees 31
Comparative research methodology 33
Non-human primate models of brain function 33
Functional neuroimaging of non-human primates 34
Chapter 2: Research design and methods 37
Research design 37
Hypotheses 37
Subjects 38
Creation of stimulus set 39
Training of subjects 41
FDG PET methodology 41
Acquisition of PET images 44
Acquisition of MR images 46
Analysis of PET images 47
T-tests 48
Whole brain averages 49
Subtraction contrasts 49
Chapter 3: Results 51
Behavioral results 51
Overview of imaging results 53
T-tests in whole brain 54
T-tests in whole brain, exclusive of cerebellum and brain stem 56
Rest-related activity 56
High social-related activity 58
Low social-related activity 59
Non-social-related activity 60
Combined social-related activity 61
Summary of t-tests 63
T-tests within resting state ROI 69
Whole brain averages 74
Subtraction contrasts 84
Chapter 4: Discussion 86
Contrasts among conditions 86
Activity in precuneus and posterior cingulate cortex 86
Activity in medial prefrontal cortex 89
Activity in insula 90
Activity in amygdala 91
Activity in fusiform gyrus 92
Activity in ventral striatum 93
Whole brain averages 94
Replicability 95
Task-positive and task-negative areas of activation 97
Variables between rest and tasks 100
Conclusion 102
Caveats and limitations 103
Directions for future research 104
Appendix 107
Maximum t-statistic values in each contrast 107
Results for each contrast, whole brain exclusive of cerebellum
and brain stem 109
Results for each contrast, resting state ROI 141
Condition averages in whole brain 173
Bibliography 176
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