What Is Reality? How Your Brain Builds a Map of the World Without Your Help

A human brain is held at a brain bank in New York City. Carlo Allegri/Reuters

Understanding reality is difficult. We aren't born with an innate sense of how the world works. Instead, we learn as we go. But how that learning happens has been a source of mystery and debate among those who study such matters.

A collection of interacting areas inside the brain known as the default mode network could be crucial. Since this patchwork was discovered, it's been thought of as a kind of bystander, a site of autobiographical memory and other passive functions of keeping information encoded in the mind. One recent study suggested its role in encoding the key plot points of an episode of Sherlock, for example.

But new research shows that the default mode network might be teaching us more about reality than we previously suspected. Deniz Vatansever and colleagues at York University and Cambridge University set out to challenge the commonly held notion about this network. "People have been thinking of default mode work as an internal model center or a network that doesn't 'do' any tasks," researcher Deniz Vatansever tells Newsweek.

In their new study, published in Proceedings of the National Academy of Sciences, Vatansever and colleagues gave 28 people a card-sorting task. They were shown four cards. They had to match them with a target card based on color, shape, or number. The catch is that subjects didn't know the rules beforehand. They had to figure out the rules of the task as they went along, getting feedback each time they tried to match the cards.

When subjects were following the rules of the task as they had learned, drawing from the feedback when trying to match the cards, there was a much higher level of activity in the default mode network than before.

Vatansever says this finding builds into a larger theory of how the mind works, one that is still the subject of much debate: predictive coding. The idea is that the mind is constantly generating hypotheses about the world around it. As a mind learns more information, those hypotheses are altered. As Vatansever puts it, this theory casts an "internal model" of what the world should look like. When new information comes in, it's compared to the model, and if it matches, the model stays the same. If it doesn't match, the model is altered.

"Once we learn rules of the environment," Vatansever says, "then the default mode network might be helping out with utilizing information to make decisions in that environment." Whether this theory holds true depends in part on whether changing levels of oxygenation in the brain, as observed by MRI, are a reliable proxy for activity in those regions.

Vatansever said he'd like to replicate this study, and to use a larger number of subjects. And going forward, he'd like to see what happens when, instead of rules set by a simple card game, people respond to real-world situations like observing a television ad for a product and being made to choose between two different brands. A test like that, he says, would show us just how much the default mode network shapes the "everyday life decisions that everybody makes."