The lonely brain: Aligning theories of loneliness with data from neuroimaging studies

Although loneliness is an unpleasant subjective experience associated with negative consequences, decades of research suggest loneliness is accompanied by adaptive cognitive changes that promote self-preservation and attempts for social reconnection. This review summarizes theoretical accounts that elaborate how loneliness alters attention and social information processing, then reviews whether findings from functional magnetic resonance imaging (fMRI) studies align with these hypothesized effects. We first examined the hypothesis that loneliness should increase general attention to monitor for potential environmental threats. Findings from resting-state studies suggested that loneliness corresponds to greater baseline activity in attention-related regions. Next, we examined the hypothesis that loneliness heightens sensitivity to the social world to protect against social threats and motivate reconnection. Here, studies showed sensitivity toward negative social information increased, whereas sensitivity toward positive social information was stimulus dependent (e.g., strangers, close others). Finally, we examined the hypothesis that loneliness enhances mentalizing to better predict social situations. Although many studies support this hypothesis, the research here is limited. However, studies do find that lonely individuals show idiosyncratic processing of the self and others. To conclude, we lay out future directions addressing some shortcomings of current fMRI studies of loneliness, and provide additional avenues to expand our knowledge of the "lonely brain."