Comparative power spectral analysis of
simultaneous elecroencephalographic and
magnetoencephalographic recordings in humans
suggests non-resistive extracellular media.
Nima Dehghani*, Claude Bédard*, Sydney S. Cash, Eric
Halgren and Alain Destexhe
Journal of Computational Neuroscience 29: 405-421, 2010.
(Special issue "Modeling Extracellular Potentials")
Abstract
The resistive or non-resistive nature of the extracellular space in
the brain is still debated, and is an important issue for correctly
modeling extracellular potentials. Here, we first show
theoretically that if the medium is resistive, the frequency scaling
should be the same for electroencephalogram (EEG) and
magnetoencephalogram (MEG) signals at low frequencies (<10 Hz).
To test this prediction, we analyzed the spectrum of simultaneous EEG and MEG
measurements in four human subjects. The frequency scaling of EEG displays
coherent variations across the brain, in general between 1/f and 1/f^2, and
tends to be smaller in parietal/temporal regions. In a given region, although
the variability of the frequency scaling exponent was higher for MEG compared
to EEG, both signals consistently scale with a different exponent. In some
cases, the scaling was similar, but only when the signal-to-noise ratio of the
MEG was low. Several methods of noise correction for environmental and
instrumental noise were tested, and they all increased the difference between
EEG and MEG scaling. In conclusion, there is a significant difference in
frequency scaling between EEG and MEG, which can be explained if the
extracellular medium (including other layers such as dura matter and skull) is
globally non-resistive.
return to
publication list
return to main page