Localization of intracerebral electrodes

The electrical resistance between a roving electrode and a remote, fixed point was measured during exploration and it was found that entry of the electrode into various structures and regions can be determined from observed changes in impedance and that this information can be used to locate directly and indirectly a wide variety of subcortical structures.

Abstract

The electrical resistance between a roving electrode and a remote, fixed point was measured during exploration. Observed changes were analyzed statistically and correlated with brain structures histologically. It was found that entry of the electrode into various structures and regions can be determined from observed changes in impedance and that this information can be used to locate directly and indirectly a wide variety of subcortical structures. The accuracy of this method is better than that of the conventional stereotactic approach because placements are made in accordance with neural rather than cranial landmarks, the distance of the electrode from known points is therefore much shortened, cumulative or consistent stereotactic errors as well as errors resulting from distortions are negated, and resolution and sensitivity can be extended to their theoretical limits. The method has been used to locate precisely subcortical structures during explorations, to reconstruct tracks of roving electrodes, to compensate for various types of distortions, to hit targets, and to recognize errors in placements. It may also be useful as an adjunct to stereotactic mapping, and in placing electrodes in brains distorted before implantation. The method should be readily adaptable to intracerebral cannulae, thermodes, and, possibly, microelectrodes.