We do it all the time, but what's actually going on in our brains as we read?

Neuroscientists have for the first time have come up with a way to observe brain activity during “natural reading,” the reading of actual text and not just individual words. The findings are already helping settle some ideas about how we read.

“It’s a key advance in understanding reading in the brain, because people are just reading normally,” says John Henderson, a psychology professor at the University of California, Davis.

Until now, neuroscientists have only measured brain activity as a volunteer fixes his or her attention on individual words. The signals of brain activity from functional magnetic resonance imaging, or fMRI, last for several seconds—too slow to keep up with natural reading, which processes several words a second.

[These suspenseful words make books thrill us]

Instead, researchers combined functional MRI with eye tracking. Lying in an MRI scanner, subjects read text on a screen while the eye-tracking device registers which word they are paying attention to at any given time.

“By tracking their eye movements as they read natural paragraphs, we can know which word they are attending to, and see the neural signal for fixation on each word,” Henderson says.

For the study, published in the Journal of Neuroscience, researchers applied the technology to test two theories about how words are represented in the brain. The first holds that words are represented by connections to the real world—what does it look like, how do I handle it, how does it make me feel—reflected in brain areas for vision, touch, emotion, and so on.

The second theory holds that words are represented as abstract symbols that interact with each other.

To test these ideas, the researchers scored the nouns in their test paragraphs for manipulability—do they refer to real objects that can be manipulated to some degree?

[Scans map the brain as people read ‘Harry Potter’]

As volunteers read the manipulable nouns, areas of the brain that deal with manipulation and carrying out physical actions lit up, lending support to the view that words are represented in the brain by connections with real actions.

By providing a window into brain activity during natural reading, the fixation-related or “FIRE” fMRI technique allows researchers to look at all kinds of unanswered questions, Henderson says, such as whether language and grammar are handled by a specific part of the brain, and whether the brain anticipates upcoming words as we read.

The discoveries may have implications not just for human psychology but also for artificial intelligence, and could help clarify dyslexia and other reading deficits.

Other researchers from UC Davis and from the University of South Carolina are coauthors of the study, which was supported by the National Science Foundation and the National Institutes of Health.