Why Do We Get Attached to Certain People?

You can sit next to hundreds of classmates over the years and remember only a few of them. Yet with one or two people, something clicks. You start saving funny things to tell them, you notice when they are not around, and before long they feel less like other people and more like part of your life.

Why does that happen with certain people and not with others? Neuroscience cannot fully answer that question yet, but research on animals and humans points to several pieces of the puzzle: reward systems that learn to value a specific person, chemical signals involved in social bonding, the calming effect of a familiar presence, and perhaps a deeper similarity in how two people see the world.

Lessons from a small, faithful rodent

Much of what we know about the biology of bonding comes from prairie voles, small rodents that are unusual because many of them form long-lasting pairs. In an influential review, researchers described a model in which the hormones oxytocin and vasopressin help process the social cues needed to recognize a particular individual, while the brain’s dopamine reward system supports reinforcement and learning. In that model, activation of both neuropeptide and dopamine receptors in reward centers during mating produces a learned preference for that partner, which researchers observe as a pair bond.

The key idea is that attachment may be partly a kind of learning. The brain links one specific individual with reward, so that person, and not just anyone, becomes something you seek out.

A story that keeps getting more complicated

For years, oxytocin was described as the “bonding hormone,” and pharmacology studies in voles supported its importance. Then, in 2023, a team used gene editing to create prairie voles with no working oxytocin receptor. Surprisingly, the mutant voles still showed a preference for their mating partner over a stranger, and parents still cared for and raised their young. The authors described the result as unexpected: social attachment could occur without oxytocin receptor signaling.

This does not mean oxytocin is irrelevant. One interpretation is that the brain has backup routes for something as important as bonding, or that animals that develop without the receptor from the start compensate in other ways. What it does show is that no single molecule is “the” cause of attachment.

The human evidence on oxytocin needs even more caution. Many studies have given people oxytocin as a nasal spray and reported effects on trust, empathy or bonding. A statistical review of that work concluded that such studies are generally underpowered and that there is a high probability that most published intranasal oxytocin findings do not represent true effects. So headlines that call oxytocin a “love hormone” are getting well ahead of the evidence.

Reward and attachment in the human brain

Human brains cannot be studied the way vole brains are, but imaging gives some clues. One study scanned 17 people who had been married for an average of about 21 years and still reported intense love for their partner. When they viewed their partner’s face, compared with the faces of a close friend and other familiar people, activity increased in dopamine-rich reward areas such as the ventral tegmental area and dorsal striatum, and in several regions previously linked to maternal attachment. The authors suggested that for some people, the reward value of a long-term partner may be sustained, while also involving brain systems tied to attachment and pair-bonding. Because this was a small group of unusually devoted couples, it shows what is possible, not what is typical.

A broad review of human attachment argues that people form several kinds of bonds, including parent-infant bonds, romantic pair bonds, and bonds with friends and wider social groups. It proposes that bonding is supported by interactions between oxytocin and dopamine in the striatum, which combine motivation with social focus, and that human attachments also draw on networks for reward, for “embodied simulation” (feeling a bit of what another person feels) and for thinking about other people’s minds. The same review emphasizes biobehavioral synchrony, the way people in close relationships come to coordinate their behavior and physiology. This is a theoretical framework built from many studies, not a single proven mechanism.

Familiar people make threats feel smaller

Part of the answer to “why these people?” may be that close others change how our brains handle stress. In one experiment, 110 adults lay in a scanner under the threat of an electric shock while holding hands with a partner (a spouse, romantic partner or platonic friend), holding hands with a stranger, or holding no hand at all. Holding the hand of a familiar partner reduced both reported distress and activity in a brain network associated with vigilance and self-control, but holding a stranger’s hand had no such regulatory effect. Notably, relationship status did not change the effect, so a close friend’s hand seemed to help about as much as a spouse’s did.

One interpretation is that attachment figures act like a shared resource. When someone familiar is with us, the brain may not need to work as hard to deal with a threat on its own. That could be part of why being apart from certain people feels uncomfortable: their presence has become part of how we cope.

Friends may see the world the way we do

There may also be a reason we click with some people in the first place. In one study, researchers mapped the friendships of an entire class of 279 graduate students, then scanned 42 of them while they watched a series of video clips. They found that brain responses to the clips were exceptionally similar among friends, and that similarity decreased as distance in the social network increased. The authors suggested that we may be exceptionally similar to our friends in how we perceive and respond to the world.

This finding is intriguing, but it is correlational. It cannot tell us whether people become friends because they already think alike, or whether spending time together makes their responses more similar. It is also one group of graduate students at one university.

What remains uncertain

Most of the detailed biology comes from rodents, and even there the picture changed sharply when oxytocin receptors were removed. Human studies are mainly correlational brain scans with modest sample sizes, and the human hormone research has serious reliability problems. Researchers also do not yet know how these systems combine to make one specific person, rather than another, feel irreplaceable. Personality, culture, shared history and simple chance almost certainly play large roles that brain studies do not capture well.

The takeaway

Getting attached to certain people seems to involve the brain learning that a particular person is rewarding, safe and familiar. Reward systems, bonding-related chemical signals, the soothing effect of a known presence, and similarities in how we see the world may all contribute. None of these is the whole story, and some popular explanations, especially about oxytocin, are much shakier than they sound. Still, the research supports something most of us already sense: the people we bond with become part of how our brains handle the world.