The older people get, the more trusting they become—a tendency that can be dangerous because it puts elders at risk for exploitation and abuse. But why does it happen? A new study suggests that older people have trouble identifying untrustworthy faces because of an age-related drop in activity in the anterior insula, a brain region that may play a role in assessing trust and risk.

Researchers at the University of California, Los Angeles, asked 119 adults who were at least 55 years old and 24 younger adults to look at pictures of faces that exhibited either trustworthy, neutral or untrustworthy qualities (according to previous analysis). Compared with the younger subjects, the older participants were much more likely to label the suspicious faces as credible and approachable. When the researchers asked a subset of the subjects to perform a similar task while undergoing a functional MRI scan, the older subjects exhibited lower activity in the anterior insula, a small region inside the cerebral cortex (below), than did the younger ones. Although the difference in activity was most pronounced when the groups looked at the untrustworthy faces, the younger subjects exhibited higher activity in the anterior insula than did their older counterparts when they looked at the trustworthy faces, too.

The findings suggest that “the anterior insula is important for assessing trust, period,” explains U.C.L.A. doctoral student Elizabeth Castle, lead author of the study published last December in the Proceedings of the National Academy of Sciences USA. The region may be responsible for the positive and negative “vibes” we get about people when we meet them, which may, unfortunately, dissipate with age.

Profile of the Anterior Insula

The anterior insula is implicated in reactions of disgust and has been shown to support general bodily awareness. The region senses our visceral states, which form the basis of gut feelings that inform decision making. Previous research has also shown that neural activation in the anterior insula is important for assessing risks, responding to breaches in trust, representing expected financial risks and predicting the safety of choice outcomes, according to the PNAS paper.