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HOW THE MIND READS OTHER MINDS
Science, May 16, 2003

Understanding what others are thinking is a human exclusive. Now
researchers are tracking how the brain performs this feat and
speculating about how it evolved

Imagine a boy sitting on a couch about to unwrap a chocolate bar. His
mother announces that she's taking him to soccer practice. He tucks
the chocolate under the couch for safekeeping and leaves. A few
minutes later, his sister comes into the room in search of her teddy
bear. When she looks under the couch she is surprised to find an
unopened chocolate bar, which she then hides behind a bookshelf. When
her brother comes home, drooling for chocolate, where will he look?

This may not seem like a difficult question: It's glaringly obvious
that the boy will look under the couch. But to get the right answer,
you have to perform an extraordinary mental feat: understand the boy's
intentions and beliefs--regardless of their accuracy--and use that
information to predict his action. And the skill doesn't come easily:
Until the age of 5 or so, children answer that the boy will look
behind the bookshelf, where they know the chocolate bar to be.

Of all the species on Earth, only humans possess what researchers call
a "theory of mind"--the ability to infer what others are thinking. "It
is extremely critical, because it underlies teaching, deception,
propaganda, all these sorts of things," says Christopher Frith of
University College London. "To get an idea from one brain into
another, that's a deeply mysterious thing we do."

It has been 25 years since scientists first began to seriously
investigate this ability to read minds. Today psychologists can chart
its development, and they link it to children's acquisition of
language and appropriate social behavior. Neuroscientists have tried
for a decade to pinpoint the regions of the brain required for a
theory of mind, and their results are now converging on a distinct
network.

This work may ultimately reveal how the brain's social wiring evolved.
On a more practical level, it is also allowing researchers to pinpoint
some of the neurological signs of autism, in which a breakdown in
theory of mind makes it difficult to understand other people's
emotions and motives. Researchers hope that they will be able to
translate these discoveries into more accurate diagnoses of autism and
point to more effective treatments.

Mind reading takes shape

The psychologists David Premack and Guy Woodruff, who first coined the
term "theory of mind," believed that chimpanzees and perhaps other
primates could read intentions. Subsequent research has shown that
primates are remarkably sophisticated in their relationships: They can
deceive, form alliances, and bear grudges for days. Chimpanzees can
even tell what another chimpanzee can and cannot see. But after
decades of studies, no one has found indisputable signs that chimps or
other nonhuman primates have a theory of mind.

IMG Ascribing intentions. Autism interferes with people's ability to
perceive complex behaviors such as teaching or coaxing in simple
animations.

Humans aren't born with a full-blown theory of mind. Children from
cultures around the world acquire the skill at roughly the same age,
and after reaching the same developmental milestones, which has led
many psychologists to conclude that the theory of mind is a specific
adaptation separate from general-purpose intelligence. "There might be
a dedicated brain system," says Frith. Researchers are still working
out how theory of mind develops in the brain. "The exciting thing
that's going to happen in the next few years is scanning children
doing [theory-of-mind] tasks at different stages," says Frith.

Autism provides more evidence that theory of mind is somewhat
independent of other skills. Autistic people do poorly on problems
like the chocolate bar test. One powerful demonstration uses
animations of geometrical shapes in motion. Nonautistic people easily
recognize when these shapes are acting like people--when two triangles
coax a circle out of a square, for example. But even highly
intelligent autistic people can't distinguish intentional movements
from random collisions. Autism, some researchers theorize, is a
selective deficit of theory of mind.

Specialized circuitry for reading people's minds hints that this
ability played an important role in human evolution. According to Paul
Bloom, a psychologist at Yale University in New Haven, Connecticut,
the evolution of language would have been impossible without it. "Our
species has come to possess this powerful theory of mind, and once you
possess that, you are then capable of understanding people referring
to things," says Bloom. His research suggests that theory of mind
makes learning words a fast, efficient process because children can
quickly recognize what their parents are trying to teach them.

Minds in the brain

In the mid-1990s, researchers using brain-imaging technology began
searching for the biological basis of theory of mind. The premise was
simple: Scan people while they perform mental tasks differing only in
that one demands the use of theory of mind. In an early study, Frith
and his colleagues had subjects read stories. The subjects then
answered questions about the stories while in a brain scanner. Only
some of the stories demanded that the subjects think about the beliefs
and intentions of the characters.

Many other teams conducted similar experiments, and each revealed a
constellation of active brain regions. Unfortunately, the
constellations were not identical from one experiment to the next.

Part of the trouble was that theory of mind is hard to isolate from
other mental tasks. Another problem was that the experiments didn't
demand mind readings on real minds--only on pictures or stories.

IMG Reading faces. The amygdala may help people judge others' emotional
states.

More recent experiments have tried to overcome these limits. Working
with Frith and other researchers at University College London, Helen
Gallagher put together an experiment based on the game of "rock,
scissors, paper." In each round, two players simultaneously choose one
object. Rock beats scissors, scissors beat paper, and paper beats
rock. Gallagher's subjects lay in a brain scanner and played the game
on a computer screen. In some cases, they were told they were playing
against a computer; in other cases, they thought their opponent was a
person. In fact, the researchers generated a random sequence of
choices. The only difference lay in the attitude of the subjects: As
the researchers confirmed in interviews after the study, when subjects
thought they were playing against a person, they tried to figure out
their opponent's strategy.

In the brain of the participant, the chief difference between playing
against a computer or a supposed human lies in one small region, a
patch of neurons above the eyes known as the anterior paracingulate
cortex, the researchers reported last year in Neuroimage . The
paracingulate turned up in older studies of theory of mind as well. It
may be responsible for the central task: separating your own mind from
someone else's. "It's being able to recognize that someone has a
different perspective than you do," says Gallagher, who is now at
Glasgow Caledonian University. She notes that the adjacent region of
the brain acts as a conflict monitor, sensing when the brain's
predictions about how the world works don't match up with reality. The
paracingulate may make a similar distinction between our own beliefs
and intentions and those of other people.

As important as the paracingulate may be, however, it can't create a
theory of mind by itself. "You have to draw on other abilities and
skills in other parts of your brain," says Gallagher. Two such regions
tend to turn up in theory-of-mind experiments. One is the temporal
pole, located near the ear. It's crucial for recalling memories,
suggesting that subjects need to dredge up past experiences to help
figure out what other people must be thinking.

The other region, known as the superior temporal sulcus, lies high up
on each side of the brain. Like the temporal pole, neuroscientists
have found it at work in many experiments not focused on theory of
mind. It is, essentially, a sensor of biological motion. The sight of
a moving car won't activate its neurons, but a moving hand will. It is
particularly sensitive to the movement of eyes and lips. It's possible
that the paracingulate gyrus depends on interpretations about body
language made by the superior temporal sulcus in order to work out
what's going on inside another person's head.

Other parts of the brain may eventually be initiated into this inner
circle of the theory of mind, but not without debate. Simon
Baron-Cohen of the University of Cambridge, for example, believes that
an almond-shaped structure known as the amygdala should be recognized
as part of the network. The amygdala has long been recognized as a key
player in the emotional life of the brain. Baron-Cohen has found that
the amygdala becomes active when subjects look at pictures of eyes to
answer questions about the depicted person's feelings and intentions.
Theory of mind comes into play, Baron-Cohen says, when "you're trying
to find out if [a stranger is] friendly or aggressive."

A few other studies have revealed the amygdala at work as well. Robert
Schultz of Yale University and his colleagues showed people animations
of "intentional" geometrical objects, as they reported in the 28
February issue of Philosophical Transactions of the Royal Society of
London . They found that only the shapes that were moving as though
they were pursuing goals triggered a theory-of-mind network--one that
included the amygdala. In the brains of autistic people, none of the
films activated this network.

Gallagher plays down the role of the amygdala, however, pointing out
that it fails to become active in most tests of theory of mind. She
suspects it plays an indirect role, primarily during development. As
children mature, she suggests, the amygdala guides their theory of
mind to situations that are socially relevant.

However, earlier this year in Neuropsychologia , Baron-Cohen and his
colleagues reported that people who sustain damage to the amygdala in
middle age--long after their theory-of-mind network has been wired
together--do worse on theory-of-mind tests than do people with
undamaged brains. In other words, it seems adults still rely on the
amygdala to read minds.

An evolving theory

Determining the neural building blocks of the theory of mind may help
researchers figure out how it evolved in our ancestors. The brain
regions identified so far all have counterparts in the brains of other
primates. It seems that the pieces of the mind-reading network were
probably all in place in the brains of early hominids. Perhaps all
that was required to create a theory of mind was to network them in
the right way. "My personal view is that it all comes from trying to
predict what some other animal is going to do next," says Frith. "It
just happens that the best way to predict what people are going to do
next is understanding mental states."

A theory of mind may even have evolved before people could understand
their own minds. That at least is the opinion of Francesca Happé, who
works with Frith at University College London. She points out that the
brain networks underlying self-awareness and an awareness of others
are intermingled. "People have struggled to find an evolutionary
explanation for self-awareness, whereas the evolutionary value of
theory of mind is clear," says Happé. Perhaps a human ancestor "could
track the intentions of others but wasn't at all self-reflective."
However it evolved, theories about theory of mind will likely keep
researchers' minds occupied for years.