The Physicist in Your Brain
Margaret Wertheim, the best-selling author of books on physics, once said that more people don’t study the subject because they think: “Oh, physics isn’t for me. I just don’t have that kind of a mind.”
Turns out, we do have that kind of mind. In fact, our brains are constantly calculating physics even if we don’t consciously realize it.
When we watch a pile of poorly stacked blocks teeter, or a pair of misdirected cars collide, we do more than witness the mishaps and cringe. Our brains constantly plot the complex actions of moving physical objects. This ability is “like having a physicist in our brains,” says Jason Fischer, an assistant professor of psychological and brain sciences in the Johns Hopkins Krieger School of Arts and Sciences. He noted that our brains not only configure the movements we’re seeing but also create a range of scenarios as to how the objects might come to behave. Watch a Magic Marker roll across a table and you might predict its descent off the edge and onto the floor, for instance.
Neuroscientists have long theorized that a specific region of our brain must handle these intense calculations. Now, Fischer, along with two professors at MIT, has pinpointed the premotor cortex and the somatosensory cortex as the brain centers responsible.Those regions hold what Fischer calls “the brain’s physics engine,” and it’s where we also organize and carry out our own physical movements.
“We asked the questions: What is the chain of events that leads the brain to understand what is happening with objects, and where in the brain are these calculations made?” Fischer says about the experiment that led to this breakthrough. “We found that regions of the brain that deal with motor planning might be doing more than just that. The brain is doing these complex physical simulations all the time.”
To find out how people perceive the motions of objects, Fischer used functional magnetic resonance imaging (fMRI) machines to monitor the brain activity of a dozen subjects. They were shown images of stacked three-dimensional blocks or billiard balls bouncing off a pool table’s edge and then asked which way the objects were likely to go. As they responded, the fMRI machine scanned their brains, showing that the premotor and somatosensory cortices experienced a marked increase in blood flow—a sign they were busy computing how the blocks or balls would move.
When we watch a pile of poorly stacked blocks teeter, or a pair of misdirected cars collide, we do more than witness the mishaps and cringe. Our brains constantly plot the complex actions of moving physical objects.
“I had some inkling that we’d see activity in the motor regions because you need a model of how the world will behave in order to plan appropriate actions on it. Effective motor planning presumes some understanding of physical behavior,” Fischer says. “But it was still surprising to see so much activity.”
Fischer’s findings could lead to more investigations, including one to learn how exactly the physics engine links up with other brain regions, creating a fuller picture of how we develop what he calls “physical reasoning.”
Once science has a better idea of that, engineers may be able to build robots that can predict physical movements as humans do. Physicians, meanwhile, could come to better understand the plight of people with apraxia, a movement disorder associated with damage to the brain. “This has opened up another area for cognitive study,” Fischer says.
The premotor cortex and somatosensory cortex perform intense computations that tell us whether a Magic Marker will roll off a table or how cars on a collision course might collide.