Inside Two Brains at Once
Hyperscanning may map out the biology of social
interaction | By Mike
May
Today's imaging technology can practically gauge brain
activity in real time. But scans of a single brain don't offer
much information about real life, according to P. Read
Montague. "There's a reason that you don't have a cocktail
party one person at a time," says Montague, professor of
neuroscience at the Baylor College of Medicine. One
partygoer--standing alone, nursing a drink, and chitchatting
to no one--hardly replicates people gabbing and gossiping in
groups. "The most important things in human life come down to
relationships with other people," says Michael Huerta,
associate director of neuroscience and basic behavioral
science at the National Institute of Mental Health.
To view those relationships, Montague recently upped the
ante using a technique he calls hyperscanning to scan the
brains of two individuals while they played a game
together.1 He selected functional magnetic
resonance imaging (fMRI) because it is noninvasive and gives a
good view of activity throughout the brain. "I'm kind of
simpleminded," Montague says. "If I want to use imaging to
study social interaction and I can't put two people in the
bore of one magnet, I have to put the scanners together."
Luckily, Baylor owns two.
These scanners predict brain activity by measuring the
so-called blood oxygenation level-dependent (BOLD) contrast,
changes in blood's magnetic characteristics related to
differences in levels of oxygenated and deoxygenated
hemoglobin. The trouble, Montague says, is that BOLD is
sluggish. It takes two seconds to scan an entire brain. To see
what goes on in each brain at the same time, the scans must be
perfectly synchronized. "Once you have that," Montague says,
"you can hunt for cross correlations between the brains, or
regions that get activated together between the subjects."
THE BRAIN'S TRUST Montague's subjects watch each
other on video monitors as they are being scanned. In one set
of experiments, they play a trust game. In essence, subjects
keep or invest money in a common pot, where the money can grow
or be taken by the opponent. All the while, Montague scans
their brains. In recent results, Montague may have found the
first social interaction map. The data, which have yet to be
published, show specific areas activated while playing such a
game.
Maps of brain activation patterns make sense for perceptual
tasks, such as audition and vision, because highly specialized
brain regions provide those capabilities. It is harder to
interpret similar maps generated for a process as complex as
social interaction. Huerta says that neuroscientists generally
think of high-level functions as being distributed or spread
over a considerable area. "Any social map would be very high
level," he says, "and it's always possible that the map is of
something else, something that you are not controlling for."
He adds, however, "The other possibility is that Montague is
absolutely right."
Other research does reveal high-level function localized to
specific areas. For instance, a recent study by Jeffrey
Schall's group at Vanderbilt University examined the activity
of single neurons in the anterior cingulate
cortex.2 In the experiment, a monkey was rewarded
if it looked at the right place for the right amount of time.
This revealed a group of neurons that responded to whether the
monkey got the reward. Schall says this suggests that part of
the anterior cingulate cortex "is sensitive to the
consequences of actions."
Paul Matthews, director of the Oxford Centre for Functional
Magnetic Resonance Imaging of the Brain, says there's
potential in Montague's work. "This might provide a way of
looking more precisely at context-dependent brain reactions."
Broader applications may exist. "This is linked to theory of
mind," Matthews adds, an understanding of why one person
empathizes with another or even knows that another exists.
This capability helps humans socialize, but deficits make up
prominent features of many diseases, including autism,
depression, and schizophrenia. Huerta says, "Knowing what's
going on in a normal brain compared to one affected by one of
these disorders would be tremendously exciting and important."
Moreover, if two brains are better than one, more brains
could be better still. So, Samuel McClure--Montague's former
graduate student and now a postdoctoral fellow at Princeton
University--plans to simultaneously image the brains of four
subjects as they make related economic decisions. Overall,
Huerta says, "this work is just getting started. Maybe
Montague will interest other scientists, especially social
psychologists, to bring their expertise and acumen to this
technology."
Mike May (mikemay@mindspring.com)
is a freelance writer in Madison, Ind.
References
1. P.R. Montague et al.,
"Hyperscanning: simultaneous fMRI during linked social
interactions," Neuroimaging, 16:1159-64,
2002.
2. S. Ito et al., "Performance monitoring by the
anterior cingulate cortex during saccade countermanding,"
Science, 302:120-2, Oct. 3, 2003.
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THINKING ABOUT ROLES:
The brain images show activity for two subjects
engaged in a social exchange. The difference in activity
may be a result of their different roles in the context
of the task. 
