When it comes to studying love, prairie voles, with their strong pair bonds, are the laboratory stars. Now researchers at the University of California, Davis, have established a primate model of monogamy they believe will be more relevant for uncovering the basis of human affection.

The researchers used PET scans to examine brain activity in male titis, small South American monkeys that form strong relationships with their mates. They discovered that lone, unpaired male titis had strikingly different patterns of brain activity than males in long-term, monogamous partnerships did. These differences were primarily found in two brain circuits: one that is involved in reward processing and another that plays a part in social recognition. These circuits appear to be necessary for pair bonding, lead researcher Karen L. Bales says. And although the regions are also implicated in rodent models of monogamy, she believes titi monkeys will ultimately be more useful for studying human bonding and social disorders, such as autism.

The scientists also studied the brains of lone males who had recently been introduced to new mates. Although the average of the monkeys’ brain activity was somewhere in between that of unpaired males and that of those in long-term partnerships, testing showed tremendous individual variation in both behavior and brain activity. “I think we can all identify with that as humans,” Bales says. “It’s not always love at first sight.”