A new wearable brain scanner can accurately record magnetic fields generated by brain activity while people are in motion. It will enable researchers to learn more about brain development and neurological conditions that can affect movement, including autism, epilepsy, stroke, concussion, and Parkinson’s disease, say researchers. 

“This advance could also make it easier to conduct brain scans in young children and individuals with neurological disorders, who can’t always remain still in conventional scanners,” said Niall Holmes, Ph.D., a Mansfield Research Fellow in the School of Physics and Astronomy at the University of Nottingham, who led the research. “Unconstrained movement during a scan opens a wealth of possibilities for clinical investigation and allows a fundamentally new range of neuroscientific experiments.”

How magnetic fields are recorded

When neurons interact, they generate a small electric current. This current produces a magnetic field that can be detected, recorded, and analyzed by sensitive magnetic sensors, using a technique called magnetoencephalography (MEG).

MEG technology can record brain signals every millisecond. By overlaying the neuronal sources of these magnetic fields onto an anatomical image of the brain, clinicians can visualize where and when specific brain activities originate. However, current MEG systems are bulky and rigid, like an old-fashioned hair dryer (where you must keep your head still for a while). Also, these sensors require cooling at or below freezing temperatures, so they can’t be placed directly on your scalp.

Now researchers at the University of Nottingham have used a new generation of magnetic field sensors called “optically pumped magnetometers” (OPMs), which operate at room temperature and can be placed close to the head, enhancing data quality. They are also flexible, allowing children and adults to move during scanning. 

The researchers also designed a magnetic shielding system that would cancel out or compensate for external magnetic fields (see “Technical background: Designing a matrix coil system” below).

Research applications

A company co-founded by Holmes and his colleagues is selling the OPM-MEG systems (which include a magnetically shielded room) to research centers in North America and Europe to conduct a variety of neuroscientific experiments.

One of the U.S. centers to use the MEG-OPM system is Virginia Polytechnique Institute and State University, which collaborated with the Nottingham team on another study to determine how well the OPM-MEG helmet worked when two individuals each wore one and then interacted.  To conduct this proof-of-concept study, two experiments involving social interaction were conducted.

“To really study how the human brain works, we have to embed people in their favorite natural environment—that’s a social setting,” said Read Montague, Ph.D., the principal investigator of the Virginia Tech team and director of the university’s Center for Human Neuroscience Research. The research was published this year in Sensors. 

For social interactions, two participants stroked each other’s hands and then played a game of ping pong.  Both experiments showed that despite large and unpredictable motions by participants, each person’s brain activity was clearly recorded.

The company is collecting data to obtain approval from regulatory bodies, including the FDA, to deploy the system in clinical populations, which can take up to five years.

Technical background: Designing a matrix coil system

The Nottingham research team constructed a system of electromagnetic coils to shield against the background magnetic-field noise and positioned them on two panels around the participant. Prior research published in Nature shows that eight large coils cancelled the background magnetic fields, but at a fixed position that only allowed small head movements.

Holmes and his team instead designed a new matrix coil system that features 48 smaller coils on two panels positioned around the participant. The coils can be individually controlled and continually recalibrate to compensate for the magnetic field changes experienced by the moving sensors, ensuring high-quality MEG data are recorded.

“This enables magnetic field compensation in any position, which makes OPM-MEG scans more comfortable for everyone and allows people to walk around,” said Holmes.

The researchers demonstrated the capabilities of the new matrix coil system with four experiments. They first wanted to show that the stationary helmet (not worn by anyone) placed inside the two coil panels could reduce background magnetic fields, which it did. Then a healthy participant wore the helmet, demonstrating that the OPMs recorded his brain function when he moved his head and that the coils cancelled the magnetic fields.

A third experiment used a wire coil as a proxy for brain cell activity because it produces magnetic fields when electric currents are applied. The wire coil attached to the helmet with OPM sensors showed that the matrix coil compensated for motion-related changes, ensuring accurate measurements. The last experiment showed that the helmet worn by a second healthy participant could produce a high-quality recording of brain activity when walking around.

“By taking advantage of recent OPM-MEG technology and designing a new magnetic shielding system, this helmet represents a novel magnetoencephalography approach that could help reveal more about how the brain works,” said Shumin Wang, Ph.D., a program director in the U.S. National Institute of Biomedical Imaging and Bioengineering (NIBIB) Division of Applied Science & Technology (Bioimaging).

Citations: Holmes, N, et al. Enabling ambulatory movement in wearable magnetoencephalography with matrix coil active magnetic shielding. NeuroImage. (2023), https://www.sciencedirect.com/science/article/pii/S1053811923003087?via%3Dihub (open-access); and Holmes N, et al. Naturalistic Hyperscanning with Wearable Magnetoencephalography. Sensors. (2023), https://www.mdpi.com/1424-8220/23/12/5454 (open-access)

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