Some people are trapped in their minds, unable to think and feel but unable to express themselves because brain injuries or illnesses have damaged their lines of communication with the outside world.
To help those in these situations, scientists at Washington University School of Medicine in St. Louis have shown they can use light to detect what's going on in someone's head. Researchers use LED light radiated from the outside of the head inward to detect activity in the brain area responsible for visual processing, then decode brain signals to determine what the person sees.
Achieving this feat required the development of neuroimaging tools and analysis techniques that move the field one step closer to solving the much more complex problem of language decoding.
The study of brain signals
Research, available online in the journal NeuroImage, demonstrates the potential of high-density diffuse optical tomography (HD-DOT). A non-invasive, wearable, light-based brain imaging technology that is sensitive and precise enough to be potentially useful in applications like this one.
"MRI could be used for decoding brain signals, but it requires a scanner and you can't expect someone to think into a scanner every time they want to communicate," says senior author. Joseph P. Culver, Professor of Radiology at Washington University.
With this optical method, users would be able to sit in a chair, wear a cap, and use this technology to communicate with people. We are not quite there yet, but we are making progress. What we have shown in this article is that, by using optical tomography, we can decode some brain signals with greater than 90% accuracy, which is very promising.Joseph P. Culver
How the technology for decoding brain signals works
When neuronal activity increases in any region of the brain, oxygenated blood rushes to fuel the activity. HD-DOT uses light to detect this blood supply. Participants wear a cap equipped with dozens of fibers that transmit light from tiny LEDs to the head. After the light has been transmitted through the head, the detectors capture the dynamic changes in the colors of the brain tissue as a result of the changes in blood flow.
Culver, first author, a student of his Kalyan Tripathy and colleagues set out to evaluate the potential of HD-DOT for decoding brain signals. They started with the visual system because it is one of the best understood brain functions.
How has the reading of brain signals been perfected?
The researchers started out simple. They recruited five participants for multiple five- to ten-minute sessions in which participants were shown a checkerboard pattern on the left or right side of the visual field for a few seconds at a time, interspersed with pauses during which there was no picture.
The researchers were able to identify the correct position of the board (left, right or not visible at all) with an accuracy of 75% to 98%.
After the first "training" the researchers made the problem more complex. They showed participants a checkerboard wedge that rotated 10 degrees per second. Three participants sat for six seven-minute shifts on two separate days. Using the same model and test execution strategy, the researchers were able to pinpoint the position of the wedge within 26 degrees.
Sound complicated? See if you understand more with this video:
The findings are a first step towards the ultimate goal of facilitating communication for people struggling to express themselves due to cerebral palsy, stroke, or other similar conditions.
"It seems like a huge leap to go through the boards to figure out which words someone is verbalizing internally," says Culver. “But many of the principles are the same. The goal is to help people communicate and what we have learned by decoding these brain signals is a solid step towards that goal. "