Age and loneliness relate to reduced trust learning and alterations in amygdala function

Functional relationships are essential for healthy aging and they rely on social cognition skills such as establishing and monitoring whom to trust. However, aging and loneliness can negatively affect social brain function, potentially leading to a vicious cycle. Using functional MRI and computational modeling, we investigated trust learning in a sample of neurotypical older (64-84 years, n = 29 f/23 m) compared to younger adults (20-33 years, n = 31 f/31 m). Older participants displayed lower initial trust and less trust learning when repeatedly interacting with a trustworthy and an untrustworthy trustee. Their basolateral and central amygdala activation was lower during trust decisions, and this was associated with less optimal trust behavior. Computational modeling also revealed that a crucial learning parameter, precision of the trust prediction error, and activation in the dopaminergic midbrain were decoupled from basolateral amygdala activation, and this effect was pronounced in lonely older adults. These findings indicate that differences in amygdala and dopamine function at older ages together with higher loneliness could impair trust learning, leading to poorer social cognition and putting individuals' sociality and well-being at risk.