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. 2019 Apr 26;6(2):ENEURO.0483-18.2019. doi: 10.1523/ENEURO.0483-18.2019

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Copyright © 2019 Wang et al.

This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license, which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed.

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Figure 4. — Examples of single-trial, time-domain, bandpass-filtered (1–50 Hz) EEG traces at electrode Fz from phantom (cantaloupe) and human participants (one with low and one with high baseline alpha-power) that illustrate the type of data gathered in this study. A, Effect of a 0.1 s inclination sweep of a Northward-pointing, 35-µT magnetic field rotating between a dip of 75° down to 75° up (Inc.UP.N, left panels) and the reverse (Inc.DN.N, right panels). This is the largest stimulus used in our experiments (150° arc, effective frequency 4.2 Hz, with the full vector of 35-µT undergoing rotation). The cantaloupe records an ∼40-µV artifact during the sweep interval but is otherwise flat. A similar artifact can be seen on humans with low alpha-power but is invisible in humans with high alpha-power without trial-averaging. B, Effect of a 0.1-s declination sweep of the horizonal magnetic component (inclination = +75°, total field = 35 µT, so horizontal component = 9.1 µT) rotating from NE to NW in the presence of a static, downward directed vertical magnetic field (33.8 µT; DecDn.CCW.N) and the reverse (DecDn.CW.N). This is a weaker electrical stimulus than used in A (only a 90° arc, a lower effective frequency of 2.5 Hz, and a quarter the field intensity). The cantaloupe shows only a weak artifact of <10 µV during the rotation. In most humans with high or low alpha-power, this artifact is hard to detect without extensive averaging. Artifacts of this sort are phase-locked to the stimulus and are easily removed using standard techniques for analyzing non-phase-locked power as noted in the EEG Methods section. Note that this human example shows an obvious drop in the alpha-power following the CCW rotation but not the CW rotation.