How do we know what other people are thinking? How do we judge them, and what happens in our brains when we do?
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 do.
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 thesis adviser.
"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 says.
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 East).
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 says.
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.