Our brains predict events in fast-forward

What happens when you look up and see a ball headed toward you? Without even thinking about it, you flinch. That might be because our brains are constantly living our lives in fast-forward, playing out the action in our head before it happens.

Humans have to navigate, and respond to, an environment that is always changing. Our brain compensates for this by constantly making predictions about what’s going to happen, says Mattias Ekman, a researcher at Radboud University Nijmegen in the Netherlands. We’ve known this for a while, but these predictions are usually associative. An example: if you see a hamburger, your brain might predict that there will be fries nearby. In a study published today in the journal Nature Communications, Ekman and other scientists focused instead on how the brain predicts motion. So they used brain scans to track what happened as participants observed a moving dot.

First, 29 volunteers looked at a white dot the size of a ping-pong ball. The dot went from left to right and then reversed directions. The volunteers watched the dot for about five minutes while scientists scanned their brains with ultra-fast fMRI. This way, the researchers know what pattern of brain activity was activated in the visual cortex while they watched the dot.

After these five minutes, the researchers showed only the beginning of the sequence to the volunteers. Here, the scans showed that the brain “autocompletes” the full sequence — and it does it at twice the rate of the actual event. So if a dot took two seconds to go across the screen, the brain predicted the entire sequence in one second. “You’re actually already trying to predict what’s going to happen,” says Ekman. “These predictions are hypothetical, so in a way you’re trying to generate new memories that match the future.”

In fact, “twice as fast as real-time” might not be the actual number because it’s limited by the brain scans, notes Ekman. An electrode placed directly in the brain might find that the rate of compression is even faster. (It’s worth noting here that the brain scan they did use, called fMRI, can sometimes be unreliable. It measures brain activity by recording how blood oxygen levels change, not by directly measuring what’s happening. And sometimes there are false positives, like when one study showed brain activity in a dead salmon.)

The study is an interesting blend of research on visual perception and memory, says neuroscientist Arjen Alink, who was not involved in the study. “The results are quite striking, because I would have expected a more subtle result,” he says. “But the effect is not minor.”

Of course, events in the real world are a lot more complex than a dot moving across the screen, and that’s the biggest limitation of the study. “It’s difficult to transfer this into the real world because there objects aren’t deterministic and, for example, a car can take a turn,” says Ekman. “So then the question is, is the brain still able to do these more complex predictions?” The next step is to figure out how well the results hold up in real-world scenarios, and what exactly is going on when someone says to look up because a ball is headed our way.