  We propose two ways of estimating the current source density (CSD) from
measurements of voltage on a Cartesian grid with missing recording points using
the inverse CSD method. The simplest approach is to substitute local averages
(LA) in place of missing data. A more elaborate alternative is to estimate a
smaller number of CSD parameters than the actual number of recordings and to
take the least-squares fit (LS). We compare the two approaches in the three
dimensional case on several sets of surrogate and experimental data, for
varying numbers of missing data points, and discuss their advantages and
drawbacks. One can construct CSD distributions for which one or the other
approach is better. However, in general, LA method is to be recommended being
more stable and more robust to variations in the recorded fields.
