Magnetoencephalography: Theory, Instrumentation, and Applications to Noninvasive Studies of the Working Human Brain

Effect of attention on responses evoked by auditorily presented words.
The subject was either ignoring the stimuli by reading (solid trace)
or listening to the sounds during a word categorization task (dotted trace);
the mean duration of the words is given by the bar on the time axis.
The field maps are shown during the N100m deflection and the sustained
field for both conditions. The contours are separated by 20 fT and the dots
illustrate the measurement locations. The origin of the coordinate system,
shown on the schematic head, is 7 cm backwards from the eye corner,
and the x axis forms a 45 angle with the line connecting the ear to the eye.
Adapted from Hämäläinen et al. (1993).
Red: a magnetometer. Green: a planer gradiometer.
Blue: an axial gradiometer. Purple: a second-order gradiometer.
Adapted from Hämäläinen et al. (1993).
Peak amplitudes (arrows) and spectral densities of
fields due to typical biomagnetic and noise sources.
Adapted from Hämäläinen et al. (1993).

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Brad Roth

Brad Roth

Professor of Physics at Oakland University and coauthor of the textbook Intermediate Physics for Medicine and Biology.