British researchers presented an improved version of the wearable magnetoencephalography: now a helmet that uses sensors 49 on the basis of magnetometers on the alkaline metals with optical pumping, can record the activity of the entire brain. The results of imaging using such a helmet comparable with the classical magnetoencephalography — both in spatial and temporal resolution. Article published in the journal NeuroImage.
From all currently existing neuroimaging methods magnetoencephalography (or MEG) is one of the most effective. Unlike fMRI with its high spatial, but low temporal resolution, and EEG, whose temporal resolution is higher and spatial — below, MEG allows us to visualize brain activity and precisely concerning time and space. The problem MEG, however, is its rather bulky design, which, moreover, does not allow the research participant to move safely (however, this in some extent different and other neuroimaging techniques).
In 2018, scientists from the University of Nottingham under the leadership of Matthew Brokers (Matthew Brookers) managed to solve this problem: they introduced a prototype of a portable MEG-a helmet that allows whoever wears it to move freely (to walk and even to play ping-pong). Instead of the classical superconducting quantum interferometers (or Squids) that are typically used in MEG, the scientists used magnetometers to alkali metal optical pumping: they modify the properties of alkali metal vapors under the influence of the magnetic field recorded by the photometer. Unlike Squids, these magnetometers do not require complicated cooling systems (for Squids, the temperature should be close to absolute zero — this is achieved by, for example, liquid nitrogen), so they can be compactly placed on the hat close to the head.
The problem, however, was partially solved: the prototype limited 13 sensors on the magnetometer, which allowed us to record activity only from a small area of the cortex (namely, the sensorimotor cortex), albeit pretty accurate. In the new work, scientists presented the amended and extended wear MEG helmet in that it uses 49 sensors, which allows to cover the entire surface of the head and, respectively, to record the activity of the whole brain.
Scientists have developed two prototypes of the new MEG of the helmet: first, more flexible, similar to the EEG cap, and the second looks like a full (and pretty massive) hat. For the location of the sensors on the helmets, the researchers used the MRI scans of the brain — and it is used to combine the recorded activity sites.
To try out MEG helmets in action, scientists recorded the brain activity of two participants of his experiment at the time, while they watched on the screen, changing shapes and at the same time moved the hand — thus it was possible to trace the activity of visual and motor cortex. To assess the effectiveness of the measurements, the experiment is also repeated in the classic MAG.
As a result, scientists managed to register the activity in the visual cortex in the gamma-range and the motor cortex in the beta range with approximately the same spatial and temporal accuracy and precision when using conventional MEG — even despite the fact that the sensors with the Squids in the classic MEG is five times larger than the sensors in the created hats. The authors said that despite the fact that both versions of the helmet can be used, and the precision is high, the preference they give solid helmet, since its sensitivity is still higher.