Similarities and differences between on-scalp and conventional in-helmet magnetoencephalography recordings
Journal article, 2017

© 2017 Andersen et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. The development of new magnetic sensor technologies that promise sensitivities approaching that of conventional MEG technology while operating at far lower operating temperatures has catalysed the growing field of on-scalp MEG. The feasibility of on-scalp MEG has been demonstrated via benchmarking of new sensor technologies performing neuromagnetic recordings in close proximity to the head surface against state-of-the-art in-helmet MEG sensor technology. However, earlier work has provided little information about how these two approaches compare, or about the reliability of observed differences. Herein, we present such a comparison, based on recordings of the N20m component of the somatosensory evoked field as elicited by electric median nerve stimulation. As expected from the proximity differences between the on-scalp and in-helmet sensors, the magnitude of the N20m activation as recorded with the on-scalp sensor was higher than that of the in-helmet sensors. The dipole pattern of the on-scalp recordings was also more spatially confined than that of the conventional recordings. Our results furthermore revealed unexpected temporal differences in the peak of the N20m component. An analysis protocol was therefore developed for assessing the reliability of this observed difference. We used this protocol to examine our findings in terms of differences in sensor sensitivity between the two types of MEG recordings. The measurements and subsequent analysis raised attention to the fact that great care has to be taken in measuring the field close to the zero-line crossing of the dipolar field, since it is heavily dependent on the orientation of sensors. Taken together, our findings provide reliable evidence that on-scalp and in-helmet sensors measure neural sources in mostly similar ways.


L.M. Andersen

Karolinska Institutet

R. Oostenveld

Radboud University

Karolinska Institutet

Christoph Pfeiffer

Chalmers, Microtechnology and Nanoscience (MC2), Quantum Device Physics

Silvia Ruffieux

Chalmers, Microtechnology and Nanoscience (MC2), Quantum Device Physics

V. Jousmäki

Aalto University

Karolinska Institutet

M. Hämäläinen

Aalto University

The Harvard-MIT Division of Health Sciences and Technology

Karolinska Institutet

Massachusetts General Hospital

Justin Schneiderman

University of Gothenburg

Chalmers, Microtechnology and Nanoscience (MC2), Quantum Device Physics

D. Lundqvist

Karolinska Institutet


1932-6203 (ISSN)

Vol. 12 7 Article no e0178602 - e0178602

Driving Forces

Sustainable development

Subject Categories

Medical Engineering



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