Using optically pumped magnetometers to measure magnetoencephalographic signals in the human cerebellum

Abstract

Key points The application of conventional cryogenic magnetoencephalography (MEG) to the study of cerebellar functions is highly limited because typical cryogenic sensor arrays are far away from the cerebellum and naturalistic movement is not allowed in the recording. A new generation of MEG using optically pumped magnetometers (OPMs) that can be worn on the head during movement has opened up an opportunity to image the cerebellar electrophysiological activity non‐invasively. We use OPMs to record human cerebellar MEG signals elicited by air‐puff stimulation to the eye. We demonstrate robust responses in the cerebellum. OPMs pave the way for studying the neurophysiology of the human cerebellum. Abstract We test the feasibility of an optically pumped magnetometer‐based magnetoencephalographic (OP‐MEG) system for the measurement of human cerebellar activity. This is to our knowledge the first study investigating the human cerebellar electrophysiology using optically pumped magnetometers. As a proof of principle, we use an air‐puff stimulus to the eyeball in order to elicit cerebellar activity that is well characterized in non‐human models. In three subjects, we observe an evoked component at approx. 50 ms post‐stimulus, followed by a second component at approx. 85–115 ms post‐stimulus. Source inversion localizes both components in the cerebellum, while control experiments exclude potential sources elsewhere. We also assess the induced oscillations, with time‐frequency decompositions, and identify additional sources in the occipital lobe, a region expected to be active in our paradigm, and in the neck muscles. Neither of these contributes to the stimulus‐evoked responses at 50–115 ms. We conclude that OP‐MEG technology offers a promising way to advance the understanding of the information processing mechanisms in the human cerebellum.

MEG Sensor Selection for Neural Speech Decoding

“…Although MEG signals might seem to be the most effective neural pathway for BCI applications, the current MEG machines are not suitable considering the high cost and immobility. Nevertheless, recent studies on OPMs [ 48 ]–[ 51 ] have provided confidence that the neuromagnetic activity can be effectively leveraged for practical BCI systems. In light of the findings reported here, it seems that with a few optimal OPM sensors it is possible to develop a fast speech-BCI for communication assistance.…”

Pragmatic spatial sampling for wearable MEG arrays

“…As we can achieve higher SNR by simply recording for longer and averaging over more data (Brookes et al, 2010), fewer sensors can be traded against longer recording times. Indeed most OPM experiments to date (that attempt a source reconstruction) have been performed with far fewer (typical 16-32) sensors than a traditional cryogenic system (Barry et al, 2019;Holmes et al, 2018;Lin et al, 2019;Roberts et al, 2019;.…”

Can electro- and magnetoencephalography detect signals from the human cerebellum?

“…These new technologies are likely to usher in a new exciting age for recordings of cerebellar MEG. In fact, a report already exists of OPMs being used to record evoked fields arising from the cerebellum (Lin et al, 2019). It furthermore seems likely that on-scalp technologies may be used to recover evoked responses from the cerebellum when doing classical median nerve stimulation as Hashimoto et al (2003) did.…”