Scientists have identified the brain's "physics engine" that helps us predict how objects in the world will behave - one of the most important aspects of cognition for survival.
This engine, which comes alive when people watch physical events unfold, is not in the brain's vision centre, but in a set of regions devoted to planning actions, suggesting the brain performs constant, real-time physics calculations so people are ready to catch, dodge, hoist - any necessary actions on the fly.
"We run physics simulations all the time to prepare us for when we need to act in the world," said lead author Jason Fischer, an assistant professor at the Johns Hopkins University in the US.
"It is among the most important aspects of cognition for survival. But there has been almost no work done to identify and study the brain regions involved in this capability," said Fischer.
Researchers, including those at Massachusetts Institute of Technology (MIT), conducted a series of experiments to find the parts of the brain involved in physical inference.
First they had 12 subjects look at videos of Jenga-style block towers. While monitoring their brain activity, the team asked the subjects to either guess where the blocks would land should the tower topple, or if the tower had more blue or yellow blocks.
Predicting the direction of falling blocks involved physics intuition, while the colour question was merely visual.
Next, the team had other subjects watch a video of two dots bouncing around a screen. They asked subjects to predict the next direction the dots would head, based either on physics or social reasoning.
The team found that with both the blocks and dots, when subjects attempted to predict physical outcomes, the most responsive brain regions included the premotor cortex and the supplementary motor area - the brain's action planning areas.
"Our findings suggest that physical intuition and action planning are intimately linked in the brain," Fischer said.
"We believe this might be because infants learn physics models of the world as they hone their motor skills, handling objects to learn how they behave," he said.
"Also, to reach out and grab something in the right place with the right amount of force, we need real-time physical understanding," he added.
In the last part of the experiment, the team asked subjects to look at short movie clips, while having their brain activity monitored.
Some of the clips had a lot of physics content, others very little. The team found that the more physical content in a clip, the more the key brain regions activated.
"The brain activity reflected the amount of physical content in a movie, even if people were not consciously paying attention to it," Fischer said.
"This suggests we are making physical inferences all the time, even when we are not even thinking about it," he said.
The research was published in the journal PNAS.
