Far-field evoked potential components induced by a propagating generator: computational evidence.

This study validates current hypotheses for the generation of so-called far-field or stationary somatosensory evoked potential (SEP) components. Changes in the volume conductor configuration and changes in the direction of nerve propagation are demonstrated to be capable of generating such components. Results are based on basic aspects of the theory of volume conduction. It is shown that in an essentially restricted volume conductor any disturbance of uniform nerve propagation in a homogeneous extracellular medium will lead to the generation of non-moving field components. A number of illustrative examples are presented in which intermingling of non-moving and propagating potential fields can be observed. These results can be helpful in unravelling complicated wave forms from the nervous system in which both types of potential field can be distinguished. It is shown that realistic changes within the volume conductor can lead to substantial far-field components. This type of volume conductor induced 'virtual generators' or 'secondary sources' is present in the peripheral nervous system and most probably also in the inhomogeneous structures of the brain.