How do we know what other people are thinking? How
do we judge them, and what happens in our brains when
MIT neuroscientist Rebecca Saxe is tackling those tough
questions and many others. Her goal is no less than
understanding how the brain gives rise to the abilities
that make us uniquely human--making moral judgments,
developing belief systems and understanding language.
It's a huge task, but "different chunks of it
can be bitten off in different ways," she says.
Saxe, who joined MIT's faculty in 2006 as an assistant
professor of brain and cognitive sciences, specializes
in social cognition--how people interpret other people's
thoughts. It's a difficult subject to get at, since
people's thoughts and beliefs can't be observed directly.
"These are extremely abstract kinds of concepts,
although we use them fluently and constantly to get
around in the world," says Saxe.
While it's impossible to observe thoughts directly,
it is possible to measure which brain regions are active
while people are thinking about certain things. Saxe
probes the brain circuits underlying human thought with
a technique called functional magnetic resonance imaging
(fMRI), a type of brain scan that measures blood flow.
Using fMRI, she has identified an area of the brain
(the temporoparietal junction) that lights up when people
think about other people's thoughts, something we do
often as we try to figure out why others behave as they
That finding is "one of the most astonishing discoveries
in the field of human cognitive neuroscience,"
says Nancy Kanwisher, the Ellen Swallow Richards Professor
of Brain and Cognitive Sciences at MIT and Saxe's PhD
"We already knew that some parts of the brain
are involved in specific aspects of perception and motor
control, but many doubted that an abstract high-level
cognitive process like understanding another person's
thoughts would be conducted in its own private patch
of cortex," Kanwisher says.
Breaking down the brain
Because fMRI reveals brain activity indirectly, by
monitoring blood flow rather than the firing of neurons,
it is considered a fairly rough tool for studying cognition.
However, it still offers an invaluable approach for
neuroscientists, Saxe says.
More precise techniques, such as recording activity
from single neurons, can't be used in humans because
they are too invasive. fMRI gives a general snapshot
of brain activity, offering insight into what parts
of the brain are involved in complex cognitive activities.
Saxe's recent studies use fMRI to delve into moral
judgment--specifically, what happens in the brain when
people judge whether others are behaving morally. Subjects
in her studies make decisions regarding classic morality
scenarios such as whether it's OK to flip a switch that
would divert a runaway train onto a track where it would
kill one person instead of five people.
Judging others' behavior in such situations turns out
to be a complex process that depends on more than just
the outcome of an event, says Saxe.
"Two events with the exact same outcome get extremely
different reactions based on our inferences of someone's
mental state and what they were thinking," she
For example, judgments often depend on whether the
judging person is in conflict with the person performing
the action. When a soldier sets off a bomb, an observer's
perception of whether the soldier intended to kill civilians
depends on whether the soldier and observer are on the
same side of the conflict.
In a future study, Saxe and one of her postdoctoral
associates plan to study how children develop beliefs
regarding groups in longstanding conflict with their
own group (for example, Muslims and Serbs in the former
Yugoslavia, or Sunnis and Shiites in parts of the Middle
They hope to first identify brain regions that are
active while people think about members of a conflict
group, then observe any changes in brain activity following
mediation efforts such as "peace camps" that
bring together children from two conflict groups.
Saxe earned her PhD from MIT in 2003, and recently
her first graduate student, Liane Young, successfully
defended her PhD thesis. That extends a direct line
of female brain and cognitive scientists at MIT that
started with Molly Potter, professor of psychology,
who advised Kanwisher.
"It is thrilling to see this line of four generations
of female scientists," Kanwisher says.
Saxe, a native of Toronto, says she wanted to be a
scientist from a young age, inspired by two older cousins
who were biochemists.
At first, "I wanted to be a geneticist because
I thought it was so cool that you could make life out
of chemicals. You start with molecules and you make
a person. I thought that was mind-blowing," she
She was eventually drawn to neuroscience because she
wanted to explore big questions, such as how the brain
gives rise to the mind.
She says that approach places her right where she wants
to be in the continuum of scientific study, which ranges
from tiny systems such as a cell-signaling pathway,
to entire human societies. At each level, there is a
tradeoff between the size of the questions you can ask
and the concreteness of answers you can get, Saxe says.
"I'm doing this because I want to pursue these
more-abstract questions, maybe at the cost of never
finding out the answers," she says.