Improved spatio-temporal measurements of visually-evoked fields using optically-pumped magnetometers

Abstract

Recent developments in performance and practicality of optically pumped magnetometers have enabled new capabilities in non-invasive brain function mapping through magnetoencephalography (MEG). In particular the lack of need of cryogenic operating conditions allows for more flexible placement of the sensor heads closer to the brain surface, leading to improved spatial measurement resolution and increased source localisation capabilities. Through recordings of visually evoked brain fields (VEF) we demonstrate that the greater sensor proximity can be further exploited to improve the temporal resolution. We use an OPM and for reference a superconducting quantum interference device (SQUID) setup to measure brain responses to standard flash and pattern reversal stimuli. We find highly reproducible signals with consistency across multiple healthy participants, stimulus paradigms and sensor modalities. The temporal resolution advantage of OPMs is manifest in a fourfold enhanced ratio of magnetic signal peak height to temporal width as compared to SQUIDs. The resulting capability of improved spatio-temporal signal tracing is illustrated by simultaneous vector recordings of VEFs in the V1 and V2 areas of the visual cortex, where a time lag on the order of 10-20 ms is consistently found. This paves the way for further studies of spatio-temporal neurophysiological signal tracking in visual stimulus processing and other brain responses with potentially far-reaching consequences for time-critical mapping of functionality in the healthy and pathological brain.

Exploring the Intersection of Brain–Computer Interfaces and Quantum Sensing: A Review of Research Progress and Future Trends

“…Magnetoencephalography: MEG is a nerve imaging technology that can measure the magnetic field near the head. [13,46,47] Recent studies have shown that MEG can be used to evaluate neurological diseases such as Alzheimer's disease, [48] Parkin-son´s disease, [49] and autism spectrum dysfunction. [50] Despite their considerable potential, existing MEGs also exhibit significant limitations.…”

“…Besides, the use of MEG is confined to magnetically shielded rooms (MSR), [13] because it needs MSR to suppress the magnetic noise from the environment, and this noise is typically many orders of magnitude higher than the neural magnetic field (fT to pT range). [51] State-of-the-art MEG systems employ around 300 SQUID, and the sensors are fixed around a patient's head. [52] In MEG, new sensors such as OPMs and high-T(c) SQUID have made it possible to sense the magnetic field on the scalp within millimeters from the scalp surface, as contrast to typical liquid-heliumcooled SQUID sensors that detect the field around ∼2 cm outside the scalp.…”

“…Traditionally, the standard MEG system requires a SQUID to configure it into a magnetic meter/gradient to measure a very tiny magnetic field appropriate for detecting brain or heart activity [51,[124][125][126] (Figure 2A). Quantum-based SQUID is a lowtemperature quantum sensor (This SQUID can be described as [126] Copyright 2011, IntechOpen.…”

“…[125,137] Several researchers have compared the effectiveness of OPM-MEG and SQUID-MEG. [46,125,134,[138][139][140] Comparative experiments were conducted and described in the examples as follows.…”

Modular optically-pumped magnetometer system

“…SQUIDs require cryogenic cooling which increases costs, limits the device portability, and increases the separation between the device and object of interest. OPMs offer reduced separation distances over SQUIDs, which is of particular interest for magnetoencephalography (MEG) [4][5][6][7], where OPM-MEG is able to offer an improved spatial [8,9], and spatio-temporal [10] resolution. These advantages can be similarly applied to the diagnostic measurement of batteries through non-invasive current mapping [11,12], and for fundamental physics research [13,14].…”