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They still can't read your thoughts just by looking at you, but researchers can now see what your brain is doing just by shining beams of light into your head. This ScienCentral News video explains.
Seeing Our Thoughts?
It kind of looks like a motorcycle helmet from the future; divided into sections with colored stripes, drilled full of holes, and stuck full of fiber optic cables. But don't be fooled -- it's actually a new brain imaging technique. Cognitive neuroscientists at the Beckman Institute at the University of Illinois, Gabriele Gratton and Monica Fabiani call it EROS and explain that it works by using harmless beams of light.
EROS stands for event related optical signal. It's optical because it uses light reflections and it's event-related because the signals it produces mirror events in the brain.
So how can light give you an accurate picture of what's happening in the brain?
"Even though we are not transparent, light does penetrate into tissue," Fabiani explains. So just like pressing a red laser pointer against your finger makes it glow red, shining light on your scalp also makes your brain give off faint reflections. As reported in "Scientific American Mind" magazine, EROS catches these reflections to create a picture of the activity in brain cells, or neurons.
Gratton and Fabiani explain that each fiber optic cable going into the helmet is either a light source or a detector. The helmet holds them in place directly on the scalp so that they touch the skin in between hairs. When the light sources are turned on, the light diffuses through the head and ultimately reflects back, getting picked up by the detectors on the way out.
When neurons are active they swell with water, causing the light to travel through them in a very different way when they are firing than when they're resting. "The particles of the light take bounces all around the tissue and depending on whether the neurons are active or inactive the bounces will change," Fabiani says.
Gratton says they can tell whether brain cells are active by how long it takes for the light to travel from the sources back to the detectors. "So light, of course, moves very quickly, but we can, with our instrumentation, detect changes in the time light takes to move through the head," he says. A computer program can then create statistically-generated images of brain activity by mapping these delays.
But you can't use just any color of light -- only certain wavelengths produce reflections. If you try pressing a green laser pointer against your finger rather than a red one, you'll see that it doesn't make your finger glow. That's because, green light, which is actually a higher-energy (but shorter wavelength) kind of light than red, gets mostly absorbed by the tissues inside our bodies. Red light and near-infrared light (longer wavelengths), on the other hand, get reflected back out. "Near-infrared light, which is a low-energy light is very useful for imaging because the substances that are in the human body tend to absorb very little light at this particular wavelength," Gratton says.
Using such low-energy light, makes EROS particularly safe. Gratton says that in fact, much more light travels through our heads when we're just sitting indoors under normal lighting than during any of their experiments.
So what makes EROS special? Science already has multiple other ways to view brain activity, but every method has its own set of limitations.
Functional MRI (fMRI) is a brain-imaging method based on showing where blood is flowing in the brain. It's based on the assumption that blood will flow to the areas of the brain where neurons are active. However, it takes much more time for blood to flow than it takes neurons to be active. "So you present a stimulus and you wait one, two, three, four seconds… and now you see a response of the brain by using functional MRI," explains Gratton. Fabiani says that although four seconds may not seem like a lot of time, it's ages in terms of brain activity. The brain acts in the range of milliseconds rather than seconds. So although fMRI gives you a very good picture of brain structure, and where in the brain activity is happening, it suffers from a time delay.
Other methods of visualizing brain activity do work in the milliseconds range, such as electrical measures like ERPs and electroencephalography. But, unlike fMRI, they don't show very accurately where the activity is happening. The type of images they produce are more like line graphs showing the intensity of activity over time, but that don't tell researchers in which region it's happening.
EROS overcomes both of these issues -- where and when activity is happening -- at the same time. As Gratton says, "With EROS we obtain this type of combination of spatial and temporal information, and the advantage is that we can get a single technology to do these two things together." The result is that EROS can generate almost real-time movies of brain activity.
"I believe that this may have very beneficial effect in the long run, both in terms of medical and clinical applications, but also in human engineering," says Gratton. For example, he says cars and other everyday machines can eventually be improved based on how our brains process what we see.
Nevertheless, EROS does have some limitations. For example, it can't be used to visualize the deepest parts of the brain and the signal it produces is fairly small. Because of the faintness of the signal, readings have to be taken multiple times to produce the statistically-generated images. However, using it together with other techniques like electrical measurements and fMRI has shown that it is just as accurate in showing what the brain is doing. Gratton and Fabiani are already using it to shed new light on complex brain activities.
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