October 2020, ScientificAmerican.com 69ing to replace classic grooming in human bonding. Some
researchers have called them the “neurochemical glue”
of human relationships.BRAINS AND MOVEMENT
an endorphIn-Infused sense of bonding and commit-
ment has been apparent in several experiments, some
of them coming from Dunbar’s laboratory. One of the
early studies showed not only that synchronous behav-
iors likely trigger the endorphin systems but also that
they do so beyond the effects produced by the physical
activity itself (the famed “runner’s high”). In one of
Dunbar’s studies, male athletes from the University
of Oxford Boat Club were invited to train on rowing
machines independently and then work out in synchro-
ny. After the exercise, researchers measured how much
pain each of the rowers could take by inflating blood
pressure cuffs on their arms until they could no longer
take the discomfort. (Measuring endorphin levels
directly is difficult, so brief pain perception is common-
ly used as a proxy.) Dunbar and his colleagues learned
that athletes who exercised in sync with others
were much more resistant to pain afterwards, and
the scientists calculated their endorphin output basi-
cally doubled.
A similar series of experiments showed that when
it comes to dancing, synchrony boosts endorphin
effects far more than do dissonant moves around the
floor. Volunteers were first taught some basic dance
moves such as “driving” (one hand is extended as if rest-
ing on top of a steering wheel, crossing from left to right
and back, while the other hand hangs relaxed along the
body) or “swimming” (knees bending rhythmically,
arms alternating from side to side as if doing the front
crawl). Afterward, the participants were divided into
groups of four and went onto the dance floor, where
everyone was handed headphones through which
music would flow. The trick, though, was that in some
groups all four volunteers heard exactly the same music
and were instructed to do the same movement routine,
causing synchrony. But in other foursomes, the mem-
bers heard different tunes or were instructed to do dif-
ferent routines—causing a weird, discordant silent dis-
co. After the dancing was over, the blood pressure cuffs
came out, and the measurements began. Once again,
those who engaged in synchrony proved more resistant
to pain, confirming that the effects are not merely
caused by dancing with others but by dancing with oth-
ers in synchrony. The scientists behind the experiments,
which were published in 2016 in Evolution and Human
Behavior, also checked how well the participants bond-
ed. As in other studies of emotional reactions, those
who boogied in sync said they felt closer to the other
participants than did those who danced separately.
Although endorphins offer a neurochemical expla-
nation for synchrony’s powerful effects, other biologi-
cal mechanisms may be at play, too. When it comes to
activity patterns within the brain, synchrony seems to
prompt different effects than does humming or shim-mying without harmony. A 2020 study using function-
al near-infrared spectroscopy—a noninvasive technique
that measures how much oxygen a particular brain
region is using, which indicates how hard it is working—
showed that while nonsynchronous movements most-
ly activate just the left hemisphere of the brain, syn-
chrony involves activation of both the left and right
hemispheres. This suggests that synchrony is a far more
complex behavior than simpler movements.COORDINATED REWARDS
other research suggests that the brain’s reward system,
including the neural structures involved in desire and
motivation, also plays a role in the power of synchrony
by creating a positive feedback loop. Using functionalmagnetic resonance imaging—another way to gauge
brain activity—a series of experiments revealed that for
those who find drumming easy, doing it in sync hikes
activity in the right caudate, a reward-related area,
which in turn makes people more likely to help the per-
son they drummed with. “We believe that during syn-
chronized drumming, the caudate activity reflects the
rewarding nature of the experience,” says Christian Key-
sers, a neuroscientist at the Netherlands Institute for
Neuroscience and the study’s lead author. “Participants
will then be more likely to engage in joint actions with
that person in the future.” People synchronize, our
reward areas of the brain activate, and that pushes us
to do more to help our partners.
Although not everyone experiences the effects of
synchrony with equal force, the experience of moving
in rhythm with others or of harmonizing voices appears
to play an important role in human societies. That is
likely why we see synchrony all over, in large sympho-
ny concerts, in dance parties and in village ceremonial
performances. When we are in sync, our hormones and
our brain activity help to smooth societal wrinkles,
keeping us together. Joining a marching band may not
be the path to world peace, but behavior like it may help
make us more tolerant and better able to see the great-
er good in wider communities.FROM OUR ARCHIVES
The Evolution of Dance. Thea Singer; June 2017.
scientificamerican.com/magazine/saEarly humans may have been able
to sustain a group size that is triple
that of the average ape because they
came up with a way to “groom”
several people at once—using voices
or body movements.
© 2020 Scientific American © 2020 Scientific American