Scientists are now able to study brain activity in the real world with enough precision to know if a subject is thinking about anything related to numbers or quantities. New research out of Stanford University, published this week in Nature, demonstrates the ability to determine when a subject either read, heard, spoke, or thought about quantities.

It's a significant finding, but this isn't the kind of mind reading you've come to know from sci-fi movies. Researchers studied three volunteers with severe cases of epilepsy who were in the hospital to have portions of their skulls removed so that electrodes could be placed directly on the surfaces of their brains. It's a technique known as electrocorticography, or ECoG, and allows for precise and detailed measurements that can't be accomplished with other methods like EEG. In clinical use, ECoG is employed prior to surgical treatment to identify where seizures originate. But Stanford researchers took the opportunity to study a region of the brain known as the intraparietal sulcus (IPS) for an extended period of time.

The IPS is key to thoughts involving numerical processing, but earlier research took place in carefully controlled experimental settings, like the inside of an MRI machine. With ECoG, researchers were able to study the volunteers in their hospital rooms. As the paper's senior author, Dr. Josef Parvizi, told Time, "You are able to see how neurons within the human brain are working in a real life setting."

To start, researchers monitored brain activity as the volunteers answered specific questions using a computer. For example, a patient would have to select if a simple mathematical statement like 2+2=5 was correct. Brain activity would spike in the IPS during these questions, while remaining unchanged during other, non-numerical inquiries.

With this data in hand, researchers then left the patients to themselves and continued to monitor their brains while recording all activity in the room using a video camera. The patients spoke with nurses, family members, and friends, watched TV, and read — activities that cannot be naturally performed from within a noisy and hulking MRI machine.

This video provided by researchers superimposes brain activity in a region of the mind known to be associated with numerical thought over a tape of patients in the "real world" setting of a hospital room.

When reviewing the video tape alongside the brain activity readout, scientists found that activity peaked in a wide range of circumstances involving quantities and numbers. Events that triggered a spike included "the visual identification of numbers, [the] enumeration of objects or individuals, as well as estimation in the temporal domain," according to the paper. Concrete examples include when patients said, heard, or read statements such as "some more Vicodin," "a bunch of people," or "an extra little bit." Other phrases included "once every hour," "the first night" and "every hour on the hour."

The range of thoughts that could trigger a spike was unexpected. But most significantly, the readings were a good match with earlier experimental results. "[This] shows that the discoveries we make through brain studies done under strictly controlled experimental circumstances, can, indeed, be generalized to real-world situations," says Dr. Thomas Thesen, director of intracranial neurophysiology research at NYU, who wasn’t involved in the study.

Of course, there's no reason to be concerned about scientists snooping on your thoughts. As Dr. Parvizi explains to Time, "The only thing that we can tell is that they were thinking about numbers" — not what numbers the patients were thinking of. The results also required an invasive procedure and only three patients were examined. Other researchers are also using ECoG to better understand which parts of the brain are involved in particular activities, helping create a more accurate map of the mind. And findings from that kind of research can lead to the next step: translating thought into commands, as another group of scientists demonstrated last year when a paralyzed woman controlled a robotic arm with only her mind.