Monkey "Pay-Per-View" Study Could Aid Understanding of Autism
DURHAM, N.C. -- Researches have found that monkeys will "pay" juice
rewards to see images of high-ranking monkeys or female hindquarters.
They say their research technique offers a rigorous laboratory approach
to studying the "social machinery" of the brain and how this machinery
goes tragically awry in autism -- a disease that afflicts more than a
million Americans and is the fastest growing developmental disorder.
an article published early online by the journal Current Biology, Duke
University Medical Center neurobiologists Michael Platt, Robert Deaner
and Amit Khera describe experiments in which they gave male rhesus
macaque monkeys juice rewards for glancing at either a neutral target
on a computer screen or images of other monkeys. By systematically
varying the juice rewards and the images -- including a gray square,
higher-ranking or lower-ranking monkeys and female hindquarters -- the
researchers could precisely measure how much reward a monkey would
"pay" to see which images.
The researchers found that the
monkeys would forego a significant amount of reward to see an image of
a higher-ranking monkey or of female hindquarters. In contrast, the
monkeys had to be "paid" more juice to view lower-ranking monkeys.
research was sponsored by The National Institute of Mental Health and
the Cure Autism Now Foundation. It will be published in the March 2005
issue of Current Biology
The aim of the study, said Platt, was
to bring into a controlled laboratory setting the kinds of social
judgments that monkeys were observed to make in the wild.
of studies of monkeys in the wild have indicated that they act as if
they make judgments about dominance rankings and of the importance of
other individuals for their own reproductive success," said Platt. "But
there have been no real quantitative experimental demonstrations that
monkeys actually process this information and use it in
"More broadly, it's important to understand
how the brain processes social information and uses it to make
decisions," said Platt. "Historically, the problem of understanding
social cognition, social evaluation and its neural basis has been a
slippery one. And in part that's because scientists haven't been able
to bring to bear the methods of experimental psychophysics to
understand these phenomena.
"So, our approach, in which we ask
the monkeys to, in a sense, put a number on how much juice they'd be
willing to 'spend' to see a particular individual gives us an
invaluable experimental system to explore the neural wiring that
underlies social cognition."
Intriguingly, said Platt, the
monkeys were not living in a colony where physical interactions could
contribute to establishing dominance hierarchies or sexual
relationships. "So, somehow, they are getting this information by
observation -- by seeing other individuals interact," he said.
findings indicate that the researchers' methods could offer rich
scientific dividends in understanding perception and the brain's social
machinery, said Platt. This knowledge can likely be applied to human
neural social machinery, he said.
"At the moment, it's only a
tantalizing possibility, but we believe that similar processes are at
work in these monkeys and in people. After all, the same kinds of
social conditions have been important in primate evolution for both
nonhuman primates and humans. So, in further experiments, we also want
to try to establish in the same way how people attribute value to
acquiring visual information about other individuals."
parallels exist, said Platt, electrophysiological, genetic and
molecular studies of monkeys in such laboratory situations could yield
important insight into the social machinery of the brain. Platt and his
colleagues have already begun exploring the neural pathways in monkeys
that govern the decision about shifting gaze to look at a target
assigned a specific reward value.
Such studies could prove
extremely important in understanding how the brain's social machinery
malfunctions in autism, said Platt.
"One of the main problems
in people with autism is that they don't find it very motivating to
look at other individuals," he said. "And even when they do, they can't
seem to assess information about that individual's importance,
intentions or expressions.
"So, what we now have with these
monkeys is an excellent model for how social motivation for looking is
processed in normal individuals. And, it's a model that we can use to
explore the neurophysiological mechanisms of those motivations in a way
we can't do in humans. For example, we can use drugs that affect
specific neural processes to explore whether we can mimic some of the
deficits found in autism in these animals."