Most people know a married couple that will say “it was love at first sight.” But is it truly possible to meet someone and instantly like or love them? And does it work the other way—can you meet someone and instantly know you don’t want to be their friend?
A new study from researchers at the University of Maryland School of Medicine suggests there may be a biological basis behind instantaneous compatibility reaction, at least in mice. The study’s findings have implications for interactions ranging from relationship compatibility to understanding diseases associated with social avoidance, such as autism and schizophrenia.
Lead author Michy Kelly, now an associate professor of anatomy and neurobiology, fell into this research after her previously un-associated work kept leading her down the same road.
While she was working at a pharmaceutical company, a group of bone researchers asked Kelly to characterize the behavior of one of their mutant mice that was missing the PDE11 protein. She observed that the mice without PDE11 withdrew socially. This piqued her interest and she began to look into mouse models of schizophrenia and antisocial behavior.
Later, as a faculty member at the University of South Carolina, Kelly examined the social behavior of mutant mice to test if they had a preference with whom they interacted.
In experiments, Kelly and her team found that PDE11 mutants preferred being around other PDE11 mutants over normal mice, while normal mice preferred their own genetic type. This discovery held true even when the researchers tested other laboratory mouse strains. When they tested another genetic variant of PDE11 with a single change in the DNA code, mice with that genetic variation preferred other mice with the same variant over any others.
“So, what is it that the mice are sensing that determines their friend preferences?,” remarked Kelly.
In additional experiments, the neuroscientist ruled out smell and body movements as contributing factors to friend preference. When presented with a scented bead from a familiar friend and one from a stranger, the PDE11 mutants favored the stranger's scent one hour after "meeting," as well as 1 week later—but not 1 day after introduction. The research team says this means the mice’s short and long-term social memory worked fine, but they had a problem coding the information into recent long-term memory—the time between short and long-term memory. Given the luxury of a week, they recover the memory and can differentiate between a friend and a stranger.
“We imagine that [PDE11] is only the first among many biomarkers of compatibility in the brain that may control social preferences,” said Kelly. “Imagine the possibilities of truly understanding the factors behind human compatibility. You could better match relationships to reduce heartache and divorce rates, or better match patients and doctors to advance the quality of healthcare as studies have shown compatibility can improve health outcomes.”
The PDE11 enzyme is located in the limbic system, the part of the brain that regulates mood and motivation. Theoretically tying the limbic system to social interaction, then, is an easy hypothesis to form; however, the underlying reason that genetically similar mice seem to prefer one other is something Kelly says she and her team still need to test further.
“What this team has done is establish a paradigm by which researchers can identify the social underpinnings of friendship in animal models,” said E. Albert Reece, MD, dean of the University of Maryland School of Medicine. "This very important finding is just the start, but hopefully will lead to exciting new avenues of biological or social treatments for diseases like schizophrenia or age-related cognitive decline in which severe social avoidance and isolation can reduce a person’s quality of life.”