The human brain undergoes significant functional and structural changes during the first decades of life, as the fundamental building blocks of human cognition are established. However, relatively little is known about maturation of brain function during these critical times. Non-invasive imaging techniques can provide information on brain structure and function, but brain scanners tend to be optimized for adult head-sizes. Traditional fixed scanners also require patients to stay completely still, which can be highly challenging for children.
A UK research collaboration aims to solve these problems by creating a wearable magnetoencephalography (MEG) system that allows natural movement during scanning. They have now used the wearable MEG for the first time in a study with young children (Nature Commun. 10.1038/s41467-019-12486-x).
The researchers, from the University of Nottingham, the University of Oxford and University College London, developed a lightweight ‘bike helmet’ style MEG scanner and used it to measure brain activity in children performing everyday activities. As well as enabling studies of neurodevelopment in childhood, this system should allow investigation of neurological and mental health conditions in children, such as epilepsy and autism, for example.
MEG measures the small magnetic fields generated at the scalp by neural current flow, allowing direct imaging of brain activity with high spatiotemporal precision. Traditional MEG systems use an array of cryogenically-cooled sensors in a one-size-fits-all helmet. Such systems are bulky and highly sensitive to any head movement.
To address these issues, the team is using optically pumped magnetometers (OPMs) to measure the magnetic fields generated by the brain. These small, lightweight sensors can be positioned on a 500 g helmet that can adapt to any head shape or size. The OPMs can also be placed far closer to the head than conventional sensors, increasing their sensitivity. The researchers also employed an array of electromagnetic coils to null the residual static magnetic field inside the magnetically shielded room, allowing individuals to be scanned whilst they move freely.
“The initial prototype scanner was a 3D printed helmet that was bespoke – in other words only one person could use it. It was very heavy and quite scary to look at,” explains PhD researcher Ryan Hill who led this latest study. “Here, we wanted to adapt it for use with children, which meant we had to design something much lighter and more comfortable but that still allowed good enough contact with the quantum sensors to pick up signals from the brain.”
The researchers designed and built the new bike helmet style scanner and used it to successfully analyse the brain activity of a two-year old (typically the hardest age to scan without sedation) and a five-year watching TV whilst their hands were being stroked by their mother. The children were able to move around and act naturally throughout.
To show that the MEG system is equally applicable to older children, the researchers also used it with a larger helmet to scan a teenager playing a computer game. Finally, they used the new scanner to examine brain activity in an adult learning to play a sequence of chords on a ukulele. Despite the substantial head and arm movement required to complete this task, clear electrophysiological responses were observed.
MEG in motion: a wearable brain scanner
“This study is a hugely important step towards getting MEG closer to being used in a clinical setting, showing it has real potential for use in children,” says Matthew Brookes, who leads the MEG research at the University of Nottingham. “The challenge now is to expand this further, realising the theoretical benefits such as high sensitivity and spatial resolution, and refining the system design and fabrication, taking it away from the laboratory and towards a commercial product.”
The researchers conclude that their study demonstrates that the OPM-based MEG system can generate high quality data, even in a 2-year-old child, and can be used to measure brain activity during naturalistic motor paradigms. “OPM-MEG, with generic helmet design, paves the way for a new approach to neurodevelopmental research,” they write.
