A few years ago, a team of researchers at New York University led by Daniela Schiller examined the neuroscience of how people form impressions of others. While their brains were being scanned in an fMRI machine, subjects were shown a photograph of a face and read six sentences about that person.

Three sentences revealed positive traits about the profile (“He picked his roommate’s package up for him on the way home from work”), and three illuminated negative traits (“He told the other student that he wasn’t smart enough”). Afterwards, the subject was asked for their overall impressions of each profile. First, a little background:

The amygdala is one of the few areas that receives information from all of the senses, making it complex enough to process the nuances of social stimuli. It controls and moderates our motivations, telling us where to go and why, navigating our social world. Damage to the amygdala in humans creates a total loss of fear, an inability to differentiate between harmful and harmless stimuli. Without it, we simply can’t learn that it’s bad to hit on the boss’s wife or drink arsenic. (Lab animals with damaged amygdalae are usually rejected by their peer groups, with tragic consequences.)

The posterior cingular cortex is the seat of autobiographical memory, attention, and the emotional influence in memory; it’s also important for spatial memory; patients with damage to the PCC show significant difficulty locating themselves or even navigating familiar terrain. Self-monitoring and self-reflection become impossible. Patients don’t know what they’re supposed to pay attention to. But the PCC is also active when we assess the value of objects, possible choices, make risky decisions and calculate bets. Stimulation of the PCC predicts exploration of a previously unexplored option: inferring the value of an alternative, whether or not we deem the change to be worth it, and what we’d have to do to get there.

Together, the PCC and amygdala help us compute first impressions of others. “These regions sort information on the basis of its personal and subjective importance and summarize it into an ultimate score, a first impression,” says Schiller.

In forming those first impressions, we automatically attend to and parse relevant information about somebody, based on how important they are to our own motivations. Our split-second reactions to other people are assessments of their value to our own social world. Outside of the lab, our impressions factor in everything from what we’ve heard about them to how often they blink.

To recap, despite some oversimplification: meeting people activates the same region of the brain responsible for assigning prices to objects. And after we’ve assigned a value to a person, we make the decision about how to orient ourselves to that person: do we want to get closer? Knowing what this person’s value is to us, do we want this person to be involved in our network?

The ideas of fear and value make great metaphors in helping us understand what's at stake during those first few seconds when we meet someone else. Fear is so primal and elicits such an immediate response, but how often do we think about the small factors that can change the way someone views us? We might be constantly checking over our shoulder because we're looking for someone in the hallway, but if the other person doesn't know that, he may interpret your actions as a little shifty. Your neutral face may look a little more menacing or indifferent than you'd like it to. 

Based on this study (and a little common sense), one of the best ways to take advantage of a first impression is to give people a reason to trust and value you. Bringing up shared social connections is probably one of the best ways to establish trust, and get what I like to call the "Not a Lunatic" seal of approval. Shared activities, mutual acquaintances, common LinkedIn connections—and don't forget about the power of a sincere Duchenne smile. Remember, you’re doing this to work around more primitive (and therefore faster) areas of the brain, and the ultimate goal is to give someone the impression that it's not only okay for the other person to get close to you, but that it would be well worth their time.

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