J. Powell et al., “Orbital Prefrontal Cortex Volume Predicts Social Network Size: An Imaging Study of Individual Differences in Humans,” Proc Royal Soc B: Biol Sci 279 (2012): 2157; P. A. Lewis et al., “Ventromedial Prefrontal Volume Predicts Understanding of Others and Social Network Size,” Neuroimage 57 (2011): 1624; J. L. Powell et al., “Orbital Prefrontal Cortex Volume Correlates with Social Cognitive Competence,” Neuropsychologia 48 (2010): 3554; K. C. Bickart et al., “Amygdala Volume and Social Network Size in Humans,” Nat Nsci 14 (2011): 163; R. Kanai et al., “Online Social Network Size Is Reflected in Human Brain Structure,” Proc Royal Soc B: Biol Sci 279 (2012): 1327.