Learning whom to trust is an important social skill, which can be affected by aging and loneliness. An often-used experimental task to study trust learning is the repeated trust game (Berg et al., 1995) where participants repeatedly invest money in another player who can be trustworthy – or not. 50 healthy, neurotypical older adults (64 to 84 years) and 62 younger adults (age: 20 to 33, see Sladky & Riva et al., 2022) played the repeated trust game (Figure 1a) while undergoing 3T functional MRI. We found that trust learning was impaired in older adults, particularly in those who reported higher levels of loneliness (Figure 1b). We used the hierarchical Gaussian filter computational model (Mathys et al., 2014) and replicated the effects from the literature in younger adults (Mikus et al. 2023, Siegel et al. 2018). Older adults, however, exhibited reduced initial trust and reduced volatility beliefs (Figure 1c). Mikus et al. demonstrate in their study that pharmacologically blocking D2/3 dopamine receptors increases volatility. Older adult showed the opposite effect, which could be explained by the observed hypoactivation in the dopaminergic midbrain during the preparation phase (Figure 1d). During outcome evaluation, older adults exhibited less activation in the posterior hippocampus, anterior insula, while thalamus, putamen, and caudate nucleus were increased (Figure 1e). Interestingly, self-reported loneliness increased activation in bilateral locus coeruleus, an effect that was further amplified in older adults (Figure 1f). Our study demonstrates how aging and loneliness could affect dopaminergic and noradrenergic mechanisms that consequently impair successful trust learning.