Once the computer has associated th

Once the computer has associated the amplitude information with its topographic location, mathematical techniques even more powerful than electrical field mapping can be brought to bear. As a result of volume conduction, potentials generated within a small brain region will be seen over a wide area of scalp. The spreading of the field to the scalp can be mathematically reduced by current source derivation methods . These spatial deblurring techniques such as the Laplacian operator can narrow the apparent distribution of the electrical field, thereby emphasizing discrete foci . The Laplacian operator supplies information about the locally occurring activity in a “reference-free” manner , taking into account the direction of the field along the scalp to define the differences between adjacent electrodes.