Title: Brain Structure Links Loneliness to Social Perception
Abstract: Loneliness is the distressing feeling associated with the perceived absence of satisfying social relationships [1Peplau L.A. Perlman D. Loneliness: A Sourcebook of Current Theory, Research and Therapy. Wiley, New York1982Google Scholar]. Loneliness is increasingly prevalent in modern societies [2McPherson M. Smith-Lovin L. Brashears M.E. Social isolation in America: changes in core discussion networks over two decades.Am. Sociol. Rev. 2006; 71: 353-375Crossref Scopus (1167) Google Scholar, 3Putnam R. Bowling Alone: The Collapse and Revival of American Community. Simon and Schuster, New York2000Google Scholar] and has detrimental effects on health and happiness [4Baumeister R.F. Leary M.R. The need to belong: desire for interpersonal attachments as a fundamental human motivation.Psychol. Bull. 1995; 117: 497-529Crossref PubMed Scopus (12010) Google Scholar, 5Cacioppo J.T. Hawkley L.C. Crawford L.E. Ernst J.M. Burleson M.H. Kowalewski R.B. Malarkey W.B. Van Cauter E. Berntson G.G. Loneliness and health: potential mechanisms.Psychosom. Med. 2002; 64: 407-417Crossref PubMed Scopus (695) Google Scholar]. Although situational threats to social relationships can transiently induce the emotion of loneliness, susceptibility to loneliness is a stable trait that varies across individuals [6Cacioppo J.T. Hawkley L.C. Perceived social isolation and cognition.Trends Cogn. Sci. 2009; 13: 447-454Abstract Full Text Full Text PDF PubMed Scopus (940) Google Scholar, 7Cacioppo J. Patrick W. Loneliness: Human Nature and the Need for Social Connection. W.W. Norton & Co., New York2008Google Scholar, 8Russell D.W. UCLA Loneliness Scale (Version 3): reliability, validity, and factor structure.J. Pers. Assess. 1996; 66: 20-40Crossref PubMed Scopus (2693) Google Scholar] and is to some extent heritable [9McGuire S. Clifford J. Genetic and environmental contributions to loneliness in children.Psychol. Sci. 2000; 11: 487-491Crossref PubMed Scopus (61) Google Scholar, 10Bartels M. Cacioppo J.T. Hudziak J.J. Boomsma D.I. Genetic and environmental contributions to stability in loneliness throughout childhood.Am. J. Med. Genet. B. Neuropsychiatr. Genet. 2008; 147: 385-391Crossref PubMed Scopus (50) Google Scholar, 11Boomsma D.I. Willemsen G. Dolan C.V. Hawkley L.C. Cacioppo J.T. Genetic and environmental contributions to loneliness in adults: the Netherlands twin register study.Behav. Genet. 2005; 35: 745-752Crossref PubMed Scopus (126) Google Scholar]. However, little is known about the neural processes associated with loneliness (but see [12Eisenberger N.I. Lieberman M.D. Williams K.D. Does rejection hurt? An FMRI study of social exclusion.Science. 2003; 302: 290-292Crossref PubMed Scopus (2471) Google Scholar, 13Kross E. Berman M.G. Mischel W. Smith E.E. Wager T.D. Social rejection shares somatosensory representations with physical pain.Proc. Natl. Acad. Sci. USA. 2011; 108: 6270-6275Crossref PubMed Scopus (393) Google Scholar, 14Cacioppo J.T. Norris C.J. Decety J. Monteleone G. Nusbaum H. In the eye of the beholder: individual differences in perceived social isolation predict regional brain activation to social stimuli.J. Cogn. Neurosci. 2009; 21: 83-92Crossref PubMed Scopus (209) Google Scholar]). Here, we hypothesized that individual differences in loneliness might be reflected in the structure of the brain regions associated with social processes [15Kanai R. Rees G. The structural basis of inter-individual differences in human behaviour and cognition.Nat. Rev. Neurosci. 2011; 12: 231-242Crossref PubMed Scopus (689) Google Scholar]. To test this hypothesis, we used voxel-based morphometry and showed that lonely individuals have less gray matter in the left posterior superior temporal sulcus (pSTS)—an area implicated in basic social perception. As this finding predicted, we further confirmed that loneliness was associated with difficulty in processing social cues. Although other sociopsychological factors such as social network size, anxiety, and empathy independently contributed to loneliness, only basic social perception skills mediated the association between the pSTS volume and loneliness. Taken together, our results suggest that basic social perceptual abilities play an important role in shaping an individual's loneliness.