Scientists Shine a Laser Through a Human Head

Summary

For the most part, anyone who wants to see what’s going on inside someone else’s brain has to make a tradeoff when it comes to which tools to use. The electroencephalograph (EEG) is cheap and portable, but can’t read much past the outer layers of the brain, while the alternative, functional magnetic resonance imaging (fMRI), is expensive and the size of a room, but can go deeper. Now, a research group in Glasgow has come up with a mechanism that could one day provide the depth of fMRI using equipment as affordable and portable as an EEG. The technology will rely on something that previously seemed impossible—shining light all the way through a person’s head.Obviously, the human head doesn’t let much light through it. For years, brain imaging techniques using light, called optical brain imaging, have struggled against that barrier to becoming widely used in research and clinical practice. Optical brain imaging primarily uses near-infrared light, to which human tissue is relatively transparent. But human heads are so good at blocking even those wavelengths that the Glasgow research group found that only a billionth of a billionth of all near-infrared photons make it through an entire adult human head from one side to the other. Statistics like these had prompted many in the field to conclude that transporting light through the deep brain was impossible, until Daniele Faccio’s group at the University of Glasgow recently did it. “Sometimes we went through phases of thinking, okay, maybe this is just impossible because we just didn’t see a signal for so many years.” —Jack Radford, University of Glasgow“There are a lot of optical techniques of monitoring brain activity which have laser detectors that are placed maybe three centimeters apart, maybe five centimeters apart. But nobody had really tried to go all the way through the head,” Jack Radford, the lead author of the study describing the work in Neurophotonics, explains. The team started with a slab of thick, light-sc...