Trust and Fear In the Brain

A brain chemical recently found to boost trust reduces activity in the brain’s fear hub, the amygdala, according to a new brain imaging study at NIH’s National Institute of Mental Health (NIMH). The finding not only provides new insight into emotion and the brain, but also suggests new approaches for treating diseases that involve social fear.

Inspired by Swiss scientists who reported last summer that a hormone called oxytocin increased trust in humans, NIMH researcher Dr. Andreas Meyer-Lindenberg and his colleagues set out to explore how this works at the level of brain circuitry. British researchers had earlier linked increased amygdala activity to decreased trust, so Meyer-Lindenberg thought that oxytocin might work by affecting the amygdala.

The researchers asked 15 healthy men to sniff oxytocin or a placebo prior to undergoing a scan that reveals brain activity. While in the scanner, the men performed tasks known to activate the amygdala—matching angry or fearful faces and threatening scenes. The threatening pictures strongly activated the amygdala during the placebo scan, but oxytocin lessened the effect. The difference was especially pronounced in response to threatening faces, suggesting a pivotal role for oxytocin in regulating social fear. Oxytocin also dampened the amygdala’s communication with areas in the upper brainstem that telegraph the fear response to other parts of the body.

This effect of oxytocin suggests possible new approaches for treating diseases thought to involve amygdala dysfunction and social fear, such as social phobia, autism and possibly schizophrenia.