ABSTRACT
In the 1920s, Hans Berger in Germany started systematically studying it, as it was detectable on the human scalp. The brain is composed of two types of cells namely, glial cells and nerve cells, or neurons. Neurons are electrically excitable, which means that in response to specific inputs each neuron can generate electric potential, called action potential. Biological tissues have a high resistivity, which is often different at different parts of the same tissue. How the electric field in the cortex gives rise to scalp potential in the electroencephalogram channels depends a lot on the tissues lying between cortical and scalp surfaces. Tissue impedance is supposed to vary from a living body to a dead body. It is possible to measure the impedance of the head tissues of a living subject using a method known as electrical impedance tomography.
