Scientists have found a way to decode (解码) a stream of words in the brain using MRI scans and artificial intelligence. The system reconstructs the main point of what a person hears or imagines, rather than trying to copy each word, a team reports. "It's getting at the ideas behind the words, the meaning, says Alexander Huth, an author of the study.

Previous efforts to decode language have relied on sensors placed directly on the surface of the brain. The sensors detect signals in areas involved in expressing words. But the Texas team's approach is an attempt to "decode more freeform thought," says Marcel Just, a professor of psychology at Carnegie Mellon University.

The new study came about as part of an effort to understand how the brain processes language. Researchers had three people spend up to 16 hours each in a functional MRI scanner, which detects signs of activity across the brain. Participants wore headphones that streamed audio from the Internet. Those streams of words produced activity all over the brain, not just in areas associated with speech and language. After participants listened to hours of stories in the scanner, the MRI data was sent to a computer. It learned to match specific patterns of brain activity with certain streams of words. Then came a paraphrased version of what a participant heard. 

The MRI approach is currently slower and less accurate than an experimental communication system being developed for paralyzed people, where people get a sheet of electrical sensors implanted directly on the surface of the brain. With an MRI-based system, no one has to get surgery. 

But future versions of MRI scans could raise moral questions. "What if you can read out the word that somebody is just thinking in their head? That's potentially a harmful thing." Huth says. This technology can't really read minds uncontrollably, though. It only works when a participant is actively cooperating with scientists. Still, systems that decode language could someday support people who are unable to speak because of a brain injury or disease. They are also assisting scientists in understanding how the brain processes words and thoughts.