Loneliness - not for the faint of heart? Effects of transient loneliness induction on neural and parasympathetic responses to affective stimuli

While loneliness has been associated with altered neural activity in social brain networks and reduced heart rate variability (HRV) in response to social stressors, it is still unclear whether these are related or parallel effects. Thus, the current study aimed to examine the relationship between loneliness and neural and parasympathetic responses to social stimuli by using an experimental induction of momentary loneliness. Sixty-three participants (18-35 y.o.) received manipulated feedback about their future relationships to induce either loneliness (Future Alone, FA; n = 31) or feelings of belonging (Future Belong, FB, n = 32) and completed a functional magnetic resonance imaging session with concomitant HRV measurement during which affective pictures with social or nonsocial content were presented. In line with our previous research, decreased vagal flexibility and more negative affect were observed in participants subjected to the loneliness induction. Furthermore, even though no significant between-group differences in neural activity were observed, the neural response to negative social vs nonsocial stimuli in the temporoparietal junction was positively associated with the parasympathetic response, and this relationship was stronger in the FA group. Taken together, these results suggest that transient feelings of loneliness may disrupt adaptive responding to environmental demands and negatively impact brain-heart interactions.