What Is Trust?

Trust is an emotional brain state, not just an expectation of behavior.

Posted Oct 09, 2018

Trust is a central part of all human relationships, including romantic partnerships, family life, business operations, politics, and medical practices. If you don’t trust your doctor or psychotherapist, for example, it is much harder to benefit from their professional advice. 

But what is trust? Here are some possibilities:

  1. Trust is a set of behaviors, such as acting in ways that depend on another.
  2. Trust is a belief in a probability that a person will behave in certain ways.
  3. Trust is an abstract mental attitude toward a proposition that someone is dependable.
  4. Trust is a feeling of confidence and security that a partner cares.
  5. Trust is a complex neural process that binds diverse representations into a semantic pointer that includes emotions.

Behaviors and verbal expressions are certainly evidence for trust—for example, when someone treats you well and says nice things to you—but these behaviors are merely evidence for the internal mental state of trust that causes them, not the trust itself. Trusting people may involve estimations of probabilities of how they will behave, but people usually trust others without any understanding of probability or any precise predictions about their behaviors. Some philosophers would say that trust is a propositional attitude, an abstract relation between an abstract self and an abstract meaning of the sentence. But the nature of these selves, relations, and meanings is utterly mysterious.

The psychological alternative that trust is a feeling of confidence and security is much more plausible than behavioral, probabilistic, and philosophical views. But it leaves unspecified the nature of this feeling. My forthcoming book, Mind-Society, proposes that trust is a brain process that binds representations of self, other, situation, and emotion into a special pattern of neural firing called a semantic pointer. Emotions like trust and love are neural patterns that combine representations of the situation that the emotion is about, appraisals of the relevance of the situation to goals, perceptions of physiological changes, and (sometimes) representations of the self that is having the emotion. 

Consider the simple case of a romantic relationship between Pat and Sam, where Pat trusts Sam to buy groceries. For this structure to operate in Pat’s brain, Pat needs to have a representation of self, which in turn is built out of a binding of current experiences, memories, and concepts. Pat’s representation of self needs to be bound with a representation of the person trusted, requiring a combination of verbal representations such as gender and sensory representations such as visual appearance. Even with just representations of the self and the person trusted, trust requires binding of bindings. Further bindings are required to incorporate representations of situations and emotions.

Trust is rarely absolute, but rather is restricted to particular situations: Pat may trust Sam to pick up the groceries but not to perform surgery. The representation of the situation, such as picking up groceries, can again be a combination of verbal, sensory, and motor depictions.

Finally, trust has an inextricable emotional dimension. Pat’s trust in Sam is not just an estimate of the probability that Sam will pick up the groceries but also a positive feeling toward Sam in this respect. In accordance with the semantic pointer theory of emotions, emotion binds a cognitive appraisal—in this case, that Sam will accomplish the required goal—with the neural representation of Pat’s physiological state, usually described as a “gut feeling.” For example, Pat’s doubts about Sam’s reliability may manifest as a nervous stomach or sinking feeling. To trust people, you need to feel good about them.

Hence, the semantic pointer in Pat’s brain for trusting Sam is a binding of five representations, each of which binds other representations, all understood as patterns of neural firings operated on by convolution. The feeling of trust arises as an emergent property of all this binding.

How can all this be going on with something as simple as Pat trusting Sam to pick up the groceries? If the brain were a serial computer having to accomplish trust by a series of step-by-step inferences, it would be puzzling how Pat could possess trust in real time. But all these bindings of bindings are accomplished in parallel by billions of interconnected neurons. Parallel processing makes it both efficient and biologically feasible that Pat has all of these representations and bindings that together emerge as trust that Sam will get the groceries.

Similarly, mistrust is an emotional process that goes far beyond estimation of low probabilities about people doing what they are supposed to. It also requires representation of the self, the person mistrusted, and the relevant aspect, but differs from trust in assigning negative emotions akin to dislike and fear. These emotional reactions emerge from the combination of cognitive appraisals about unsatisfied goals and unpleasant physiological reactions to a creepy person. Mistrusting someone is not just a prediction of betrayal, but also a bad emotional feeling about the untrustworthy person.