I believe trust is associated with
positive emotions you feel with someone as opposed to feeling suspicion and resentment. For instance, if you're forced to trust someone whom you don't have a positive encounter with, cortisol is released in response to stress, while oxytocin decreases
In the source below, an experiment of trust was conducted on individuals. They found that two specific brain regions were actively engaged when someone thought they were trusting a close friend. Increased activity of the
ventral striatum and medial prefrontal cortex were correlated with positive social value signals when participants made decisions based on a belief they were playing with a good friend. Therefore, the ventral striatum is considered a key pathway in human reward processing and positive emotions.
The medial prefrontal cortex is associated with how we perceive another person's mental state and monitoring what's happening outside our current focus of attention. The medial prefrontal cortex also plays a role in decision-making as well retrieving and consolidating memories.
Together, these brain regions provide evidence that participants felt a greater social reward when they believed their good friend had reciprocated cooperation during the game.
Source:
https://www.jneurosci.org/content/35/21/8170