Mapping the chattering of neurons is a tricky undertaking. Arguably the best tool for eavesdropping in real time—by detecting the weak magnetic fields emitted by communicating neurons—comes with a huge caveat: Participants must keep their heads absolutely still inside an enormous scanner. That makes the method, magnetoencephalography (MEG), a no-go for young children, and it nixes studying brain behavior while people are moving. Now, scientists have developed the first device to solve those problems, a masklike instrument that can transmit brain signals even when the wearer is moving.
Despite some limits on how much of the brain’s activity can be mapped at once, neuroscientists are excited. “This is remarkable,” says MEG researcher Matti Hamalainen of Massachusetts General Hospital in Boston, who wasn’t involved in the study. “MEG is moving forward conceptually into a new era.”
When neurons interact with one another, their weak electrical current generates a tiny magnetic field. To measure it with conventional MEG, scientists have people stick their heads inside a scanner like an “old-style hair dryer at a salon,” explains physicist Richard Bowtell of the University of Nottingham in the United Kingdom. Inside the scanner are superconductors, loops of ultrasensitive magnetic sensors that need to be kept extremely cold by liquid helium.
It’s an incredibly powerful technology, Bowtell says, but a person moving just 5 millimeters will ruin any attempt to read their brain activity. To study the brain during motion-related tasks, MEG researchers have devised ingenious ways to simulate movement in virtual reality.
To work around such workarounds, Bowtell’s team created a wearable 3D-printed mask that, instead of using superconductors as sensors, relies on 13 small glass cubes filled with vaporized rubidium. These optically pumped magnetometers (OPMs) get to work when a laser pulses through the vapor, lining up the atoms in its path. When neural current from the brain generates a small magnetic field, it knocks the atoms out of formation. A sensor on the other side measures fluctuations in the light from the laser to paint a map of brain activity.
Elena Boto, a physicist at the University of Nottingham, was the first to try the mask out. To compare it to a conventional scanner, she performed a series of tasks—including bending and pointing her finger, drinking from a cup, and bouncing a ball on a paddle—while using both devices. Even though her head bobbed to and fro in the mask, the brain activity recorded was practically identical to that of the fixed scanner, the researchers report today in Nature.
Some challenges remain. To counteract interference from Earth’s magnetic field, researchers had to set up two large panels with magnetic coils on either side of the mask, limiting Boto’s range of motion. Expanding the range of motion to allow for something like walking is a technically difficult chore.
But the biggest hurdle is cost. The OPM sensors, designed and manufactured by QuSpin of Louisville, Colorado, are expensive, each costing about $7000. The 13 sensors in the current mask could target only one region of the brain at a time—many dozens more would be needed to give scientists full-brain coverage. The cost of doing that, nearly $1 million, would be prohibitively expensive for many researchers, Bowtell says, though he expects the price to drop as the technology matures.
But Timothy Roberts, a neuroradiologist who works with children with autism at the Children’s Hospital of Philadelphia in Pennsylvania, says MEG masks like this one would be worth it. Neuroscientists could one day use them to track early brain development or to record brain signals in adults with movement disorders like Parkinson’s disease. Or, says Roberts, to finally get a good look at the brain activity of his often fidgety patients. “Asking a child with autism to sit still is not very easy. Asking a toddler to sit still is impossible. … I think this work is transformative.”