Next time you want to see a trailer of your favorite movie, don’t search for it on YouTube--just watch it in your head. Think I’m crazy? Think again. A team led by professor Jack Gallant of UC Berkeley recently found that people can watch videos in their head without seeing anything physical through their eyes.

Subjects in the study first watched YouTube videos for several hours straight and were then asked to replay the videos in their mind. While the subjects recounted the videos, researchers recorded a spatial map of blood oxygen levels in their brains using functional Magnetic Resonance Imaging (fMRI). This imaging technique separates the brain into small three-dimensional regions and determines which parts of the brain are active at a given point in time. Complex calculations carried out by computers then convert the fMRI signals into blurry but distinctive collections of images that correspond to the videos the subjects had watched previously.

The study represents a major leap towards reconstructing mental imagery, but it is only the first step of a much more ambitious effort. The team ultimately hopes to use their experience decoding videos that a subject has watched previously to learn how to read out mental images in real time. Further progress in this direction could lead to applications like reading the thoughts of deaf and mute people or allowing cerebral palsy or paralysis patients to control mechanical devices.

Because the brain is composed of so many interacting pieces, it is not surprising that a tremendous amount of information can be extracted by measuring the activity in different regions. With more sophisticated models and improved measurement technology, there is no telling what sorts of information we might be able to extract from the brain in the future.