Amygdala volume and functional connectivity predict individual differences in human social networks and social cognition

Thesis (Ph.D.)--Boston University PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.Comparative neuroanatomists hypothesize that the amygdala is one brain region that might be important for handling the demands of complex social life. In this dissertation, four studies were conducted to examine relationships between individual differences in amygdala volume and functional connectivity, social network size, and social cognitive functions . Using structural MRI, Study 1 demonstrated the first evidence that amygdala volume uniquely predicts the size and complexity of social networks in healthy adults. Using resting-state functional connectivity analysis, Study 2 demonstrated that healthy adults who have larger and more complex social networks not only have larger amygdala volumes but also amygdalae with stronger functional connectivity. Study 3 and 4 used structural MRI and a newly developed and validated clinician-based rating scale to assess relationships between atrophy in large-scale brain networks anchored in the amygdala and social cognitive impairments in a sample of frontotemporal dementia (FTD) patients. Results demonstrated that patients with the greatest atrophy in a mesolimbic-social affiliation network exhibited the most severe socioemotional detachment, whereas patients with the greatest atrophy in an interoception-social aversion network exhibited the most severe lack of social apprehension, and patients with the greatest atrophy in a sensory association-social perception network exhibited the most severe lack of awareness or understanding of others' social and emotional behavior. All findings were anatomically specific to the amygdala or amygdalar networks in that individual differences in social network characteristics and social cognitive impairment could not be explained by the volume, strength of functional connectivity, or degree of atrophy in other, control, brain regions and networks. Taken together with previous human neuroimaging and neuropsychology work, findings from this dissetiation suggest that the amygdala patiicipates in large-scale brain networks to conduct aspects of social cognition that are needed to forge and maintain social relationships