Physiological Foundations of Quantitative EEG Analysis - Quantitative EEG Analysis Methods and Clinical Applications - page 20

aspects of both local and global theories, but typically with more emphasis on one or
the other, as outlined by Nunez and Srinivasan [2, 18].

1.13 Summary: Brain Volume Conduction Versus Brain Dynamics

The physical and physiological aspects of electroencephalography are naturally sep-
arated into two disparate areas, volume conduction and brain dynamics (or neocor-
tical dynamics ). The first area is concerned with the relationships between current
sources P ( r , t ), the so-called “EEG generators,” and their corresponding scalp poten-
tials. The fundamental laws governing volume conduction, charge conservation,
and Ohm's law leading to Poisson's equation (1.3) are well known, although their
application to EEG is nontrivial. The time variable in Poisson's equation acts as a
parameter such that the time dependence of an EEG at any location is just the
weighted space average of the time dependencies of contributing brain sources. The
fact that EEG waveforms can look quite different at different scalp locations and be
quite different when recorded inside the cranium is due only to the different weights
given to each source region in the linear sum of contributions. The resulting
simplification of both theory and practice in EEG is substantial.
The issue of brain dynamics, that is, the origins of time-dependent behavior of
brain current sources producing EEGs, presents quite a different story. Although a
number of plausible, physiologically based mathematical theories have been pro-
posed, we may be far from a proven theory. Nevertheless, even very approximate,
speculative, or incomplete dynamic theories can have substantial value in the forma-
tion of conceptual frameworks supporting brain function. Such frameworks should
provide a rich intellectual environment for designing new experiments and for eval-
uating quantitative EEG methods. In particular, several dynamic models, with
emphasis ranging from more local to more global dynamics, can be combined with
volume conduction models as a means of testing the quantitative EEG methods
proposed in this topic.

References

[1] Berger, H., “Uber das Elektroenzephalorgamm des Menschen,” Arch. Psychiatr. Nervenk.,

Vol. 87, 1929, pp. 527-570.

[2] Nunez, P. L., and R. Srinivasan, Electric Fields of the Brain: The Neurophysics of EEG, 2nd

ed., New York: Oxford University Press, 2006.

[3] Braitenberg, V., and A. Schuz, Anatomy of the Cortex: Statistics and Geometry , New York:

Springer-Verlag, 1991.

[4] Nunez, P. L., Neocortical Dynamics and Human EEG Rhythms, New York: Oxford Uni-

versity Press, 1995.

[5] Krieg, W. J. S., Connections of the Cerebral Cortex , Evanston, IL: Brain Books, 1963.

[6] Krieg, W. J. S., Architectronics of Human Cerebral Fiber System , Evanston, IL: Brain

Books, 1973.

[7] Libet, B., Mind Time , Cambridge, MA: Harvard University Press, 2004.

[8] Nunez, P. L., and R. Srinivasan, “Hearts Don't Love and Brains Don't Pump: Neocortical

Dynamic Correlates of Conscious Experience,” Journal of Consciousness Studies, Vol. 14,
2007, pp. 20-34.