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Bioelectromagnetism

Afer the demonstration of Du Bois Reymond on the electrical nature of the action potential, Richard

Caton (1842–1926), British physiologist at the Royal Infrmary School of Medicine in Liverpool, inves­

tigated the spontaneous electrical activity of animal brain in rabbits, dogs, and monkeys in 1875. He

placed electrodes on the surface of the animal’s brain and measured the potential changes. In particular,

he found that shining a light toward the animal’s eyes caused a change in the electrical potential of a cer­

tain part of the animal brains. Tis is believed to the earliest record of an electroencephalogram (EEG).

In 1890, Adolf Beck (1863–1942), a Polish physiologist at Cracow, described the discovery of spontane­

ous fuctuations in the electrical activity of animal brains in rabbits and dogs. He was nominated three

times for the Nobel Prize in physiology or Medicine, but he never received it. Beck’s fnding was done

independently of Caton’s observation (Beck, 1890).

In 1924, Hans Berger (1873–1941), professor, psychiatrist at the University of Jena, Germany, using a

double-coil galvanometer made by Siemens, succeeded in fnding the decrease a human brain’s elec­

trical activity following sensory stimulation. Tis was the frst record of the electrical activity of the

human brain, called electroencephalogram (EEG) from the surface of the skull. In 1931, he identifed

major α (8–12 Hz) and β (13–60 Hz) rhythms. He applied this new technique to the study of epilepsy

and to the efects of activities such as mental efort. In 1941, unable to cope with the growing realization

that he was mentally ill, he hanged himself (Rowbottom and Susskind, 1984). Afer visiting Berger’s

laboratory from England, William Grey Walter (1910–1977), an American-born British neurophysiolo­

gist, improved the original Berger’s EEG machine with an automatic frequency analyzer. As mentioned

above, physiological understanding of the heart and brain including heart rhythm (ECG) and brain

rhythm (EEG) appeared in the frst half of the twentieth century. Tis understanding with the advance

of electronic technology brought the introduction of transistorized pacemakers and defbrillators and

use in clinic in the second half of the twentieth century.

2.5.1.2 Electric Properties of Biological Systems

In order to understand the interaction between electromagnetic felds and biological systems in bioelec­

tromagnetism, the knowledge of the electric (dielectric) properties of biological systems is the key for

providing experimental and theoretical insights into the bioelectromagnetic phenomena. Elucidation of

the electrical properties of living organisms is important for measuring the ECG, EEG, etc. generated by

living organisms, for the response of living organisms to external stimuli, and for clarifying the safety

of medical devices. As mentioned in previous sections, the use of electricity and magnetism has a long

history in electromagnetism. From the nineteenth century, the electric properties of tissues and cell

suspensions were investigated. Te theory to explain bioelectric phenomena was gradually developed.

In the 1870s, Ludimar Hermann (1838–1914), a Berlin-born physiologist and an assistant to Emil du

Bois Reymond, was concerned with the electric and chemical actions which take place during muscle

and nerve activity (Rowbottom and Susskind, 1984) and contributed greatly to the model from which

the electric properties of the nerve fber are described in terms of resistances and capacitors. Tis means

that the membrane of the nerve fber could be represented by a number of resistors and capacitors in

parallel (McComas, 2011). Tis model becomes very useful for neurophysiologists. Herman determined

the resistance anisotropy-ratio of muscle and nervous tissues with DC (Hermann, 1872). Further, based

on the cable theory, Hodgkin and Rushton developed the mathematical theory of nerve fber conduc­

tion. Hermann coined the term of format in acoustic phonetics.

Early electrophysiological research studies included the study of the electrical conductance of blood

and tissue. Te study of excitability and contractility of membranes was also included. Contractility was

recognized to be caused by the nonlinear properties of the membranes above certain threshold values.

Stewart, Philippson, and Höeber carried out experiments on red blood cells. George Neil Stewart (1860–

1930) was Scottish-Canadian physiologist, professor at Western Reserve University. He studied 1 year as

a post-graduate with Emil du Bois-Reymond in Berlin in 1886–1887. He measured the resistance of blood

at low frequency range (Stewart, 1899). Afer the introduction of the Wheatstone bridge and Kohlrausch

bridge, the determination of the electrical properties of blood was introduced frst by Höber. In 1912,