In vitro model of far-field stationary potentials: boundary effects on propagated potentials.

Far-field stationary potentials have been said to result from several factors such as changes in the anatomical orientation of the direction of a propagating nerve action potential (AP) or local modifications of the impedance in the external volume conductor by changes in its geometry or resistivity. In the case of an impedance variation due to the presence of boundaries in the geometry of the medium, the findings reported in this paper showed that it is possible to record simultaneously AP and stationary potentials which we have called boundary potentials (BPs). The BP amplitude depended on the number of active axons at the boundary, on the distance between the boundary and one of the recording electrodes, and on the local impedance variation. Its polarity depended only on the direction of the AP propagation relative to the sign of the local impedance modification, the recording electrodes being in the same relative positions with respect to the direction of the propagating impulse. Finally, the recording of a BP remained possible whatever the relative position of the boundary and of the recording electrodes. These findings are in accordance with some clinical observations not yet explained.