Journal of Neurophysiology, Vol 38, Issue 2 356-368, Copyright © 1975 by APS
Theory of current source-density analysis and determination of conductivity tensor for anuran cerebellum
C. Nicholson and J. A. Freeman
The theoretical basis of current source-density (CSD) analysis in the
central nervous system is described. Equations relating CSD, the current
flow vector, and the extracellular field potential are given. It is shown
that the CSD provides superior resolution of neuronal events when compared
to conventional field-potential analysis. Expressions for the CSD in
rectangular Cartesian coordinates are derived, including the general case
of anisotropic, inhomogeneous conductive tissue, and a coordinate system
rotated with respect to the principal axes (APPENDIX). The minimum number
of spatial dimensions for accurate CSD analysis is discussed. The
conductivity tensor was experimentally measured in frog and toad cerebella.
All three principal components of the tensor were evaluated and their
spatial gradients determined to be negligible. It was also shown that the
conductivity was independent of potential. Thus the anuran cerebellum is
anisotropic, homogeneous, and ohmic. On the basis of these results the
appropriate mathematical expression for the CSD was selected.
