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A Polarity Alignment Method for Group-Averaging of Event-Related Neural Signals at Source Level in MEG Beamforming Applications

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Abstract

Brain waveforms reconstructed at source level, like in beamforming, suffer polarity indeterminacy, which precludes direct group averaging of associated waveforms. We describe a polarity alignment method as an alternative of averaging rectified (i.e. absolute value) waveforms. Using MEG from an auditory localisation task, we compare the ability of the two approaches to enable signal detection in the primary auditory cortex over increasing sample size. The two methods are comparable in signal detection sensitivity, but the alignment method preserves group-average polarity alternation.

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Fig. 1

Data Availability

The authors confirm that the MATLAB code supporting the findings of this study is available within its supplementary materials.

Notes

  1. MATLABtm code for PAM and for PC1 is available as supplementary material.

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Acknowledgements

The authors thank Dr. Olivier Collignon for providing the MEG data. Research supported by a Canada Graduate Scholarships—NSERC—Alexander Graham Bell from the Natural Sciences and Engineering Research Council of Canada to AD.

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Authors and Affiliations

  1. Département de psychologie, Université du Québec à Montréal, Case postale 8888, succ. Centre-ville, Montreal, QC, H3C 3P8, Canada

    Audrey Doualot & André Achim

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  1. Audrey Doualot
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  2. André Achim
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Correspondence to Audrey Doualot.

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Both authors declare no conflict of interest.

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Doualot, A., Achim, A. A Polarity Alignment Method for Group-Averaging of Event-Related Neural Signals at Source Level in MEG Beamforming Applications. Brain Topogr 34, 269–271 (2021). https://doi.org/10.1007/s10548-021-00829-1

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  • DOI: https://doi.org/10.1007/s10548-021-00829-1

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