by University of Maryland School of Medicine
Have
you ever met someone you instantly liked, or at other times, someone
who you knew immediately that you did not want to be friends with,
although you did not know why?
Popular author Malcolm Gladwell examined this phenomenon in his best-selling book, Blink. In
his book, he noted that an "unconscious" part of the brain enables us
to process information spontaneously, when, for example, meeting someone
for the first time, interviewing someone for a job, or faced with
making a decision quickly under stress.
Now,
a new study from the University of Maryland School of Medicine (UMSOM)
suggests that there may be a biological basis behind this instantaneous
compatibility reaction. A team of researchers showed that variations of
an enzyme found in a part of the brain that regulates mood and
motivation seems to control which mice want to socially interact with
other mice—with the genetically similar mice preferring each other.
The
UMSOM researchers, led by Michy Kelly, Ph.D., Associate Professor of
Anatomy and Neurobiology, say their findings may indicate that similar
factors could contribute to the social choices people make.
Understanding what factors drive these social preferences may help us to
better recognize what goes awry in diseases associated with social
withdrawal, such as schizophrenia or autism, so that better therapies
can be developed.
The study was published on July 28 in Molecular Psychiatry, a Nature publication.
"We imagine that this is only the first among many biomarkers of compatibility in the brain that may control social preferences,"
said Dr. 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."
A
succession of unlikely events and circumstances over the years
eventually culminated in this research project, according to Dr. Kelly.
While
she was working at a pharmaceutical company, a group of bone
researchers asked Dr. Kelly to characterize the behavior of one of their
mutant mice that was missing the PDE11 protein. She observed that these
mice without PDE11 withdrew socially, so she knew that PDE11 had to be
in the brain. She remembered a study that used a mouse model of
schizophrenia in which the researchers damaged the brain's hippocampus
leading to antisocial behavior. She then looked at this part of the
brain in healthy mice and found where the PDE11 protein was hiding.
Later, as a faculty member at University of South Carolina, she continued studying the social behavior of mutant mice in
terms of their social reactions to scent. In the lab, researchers took
wooden beads rubbed all over with pungent, airborne pheromones from one
group of mice, and placed them in an enclosure with a second group. A
mouse presented with one bead from a familiar friend and another from a
new stranger mouse would typically spend more time investigating the
bead with the stranger's scent on it. When researchers looked at the
PDE11 mutant's preferences, they favored the stranger's scent one hour
or one week after meeting their friend, but one day after
meeting—considered recent long-term memory for a mouse— their social
memory seemed fuzzy, and they did not differentiate between a friend and
a stranger. To the researchers this meant, the mice's short and
long-term social memory worked fine, but there was a problem coding the
information into recent long-term memory—the time between short and
long-term memory. Given more time, they would eventually recover that
memory.
A
student working in the laboratory offhandedly remarked that he noticed
children with autism prefer to interact with others that have autism.
So, Dr. Kelly decided they should test to see if the PDE11 mutants and
normal mice had a preference with whom they interacted. The researchers
found that PDE11 mutants preferred being around other PDE11 mutants over
the normal mice, while normal mice also preferred their own genetic
type. This discovery held true even when 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?" said Dr. Kelly. "We
eliminated smell and body movements as contributing factors, but we
still have some other ideas to test."
"What
this team has done is to establish a paradigm by which researchers can
identify the social underpinnings of friendship in animal models," said
E. Albert Reece, MD, Ph.D., MBA, Executive Vice President for Medical
Affairs, UM Baltimore, and the John Z. and Akiko K. Bowers Distinguished
Professor and Dean, 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."