Principles of Electric Field Generation for Stimulation of the Central Nervous System
This chapter focuses on the various principles of electric field generation for stimulation of the central nervous system (CNS). Electrical stimulation is used to study the form and function of the nervous system and is a technique to restore function following disease or injury. Applications of electrical stimulation for restoration of function include generation, inhibition, and modulation of brain activity. The electrical properties of the central nervous system are inhomogeneous, meaning that they vary at different positions within the tissue because the neuronal and glial elements have wide-ranging dimensions, varying orientations, and different packing densities. The electrical properties of the central nervous system are anisotropic, meaning that they vary along different directions through the tissue because of the nonrandom orientation of neural elements. In particular, the white matter has anisotropic conductivity as current can travel more easily in the direction parallel to the axons than in the direction transverse or perpendicular to the axons. The extracellular potentials are also dependent on the electrical properties of the tissue. The electrical conductivity of the tissue also varies with position within the CNS. The voltages generated in the central nervous system by applied currents can be calculated using quantitative approaches, and the results can be used to interpret the observed effects of stimulation and to design electrodes and stimuli appropriate for the intended application. © 2009 Elsevier Ltd All rights reserved.
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