Electrical Current Distribution in the Brain During Application of Diffuse Electrical Currents
Abstract
Early measurements of electrophysiological properties of the brain were centered around correlations between the electrical properties of neural tissue and physiological events. With the advent of electroanesthesia and electrotherapy, emphasis is being shifted to studies of the effects of electrical stimulation on specific tissues. This requires a knowledge of the distribution of currents applied to the head by means of external electrodes. It is the intent of this dissertation to examine means for measuring such currents at local sites within the brain. In the past, current density measurements have been avoided due to the problems associated with the electrodes required for such measurements. Therefore most of the existing data relative to current density within the brain has been obtained from calculations based on potential measurements. These calculations have assumed that the tissue was both isotropic and homogeneous with respect to the electrical properties. It is well known that neural tissues within the brain are neither isotropic nor homogeneous. It is therefore desirable that current densities be determined directly. Due to the fact that the electrical properties of the brain tissues change greatly upon death, it is necessary that current density measurements be made in vivo. As you, the reader, wend your way thru this dissertation, you will be struck by the amount of information that is devoted to resistance, resistivity, equivalent conductance and instrumentation methods devoted to the measure of these factors. Is this material necessary to the understanding of direct current density measurements? There is no doubt in the mind of the author that an understanding of these factors is essential to understanding the measurement of current density. A current density measuring system has been devised and investigated by the author in which simultaneous measurements are made of current density and resistivity. This system has been investigated in the laboratory with hundreds of in vitro tests for validity using various physiological solutions. Measurements have also been made in vivo using stumptail macaque monkeys.